How much bigger could Earth be before rockets wouldn't work?(space.stackexchange.com)
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How much bigger could Earth be before rockets wouldn't work?
https://space.stackexchange.com/questions/14383/how-much-bigger-could-earth-be-before-rockets-wouldnt-work
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For anyone interested in the history of rocket propellants, I highly recommend "Ignition!" by John D. Clark[0]. It has plenty of chemistry if you're into that, but even if you're not (like me) it's an enjoyable read.
[0] https://library.sciencemadness.org/library/books/ignition.pd...
[0] https://library.sciencemadness.org/library/books/ignition.pd...
Just one of dozens of amazing passages in this book (page 48):
> "... its density was a little better than that of the other acid, and it was magnificently hypergolic with many fuels. (I used to take advantage of this property when somebody came into my lab looking for a job. At an inconspicuous signal, one of my henchmen would drop the finger of an old rubber glove into a flask containing about 100 cc of mixed acid -and then stand back. The rubber would swell and squirm for a moment, and then a magnificent rocket-like jet of flame would rise from the flask, with appropriate hissing noises. I could usually tell from the candidate's demeanor whether he had the sort of nervous system desirable in a propellant chemist.)"
> "... its density was a little better than that of the other acid, and it was magnificently hypergolic with many fuels. (I used to take advantage of this property when somebody came into my lab looking for a job. At an inconspicuous signal, one of my henchmen would drop the finger of an old rubber glove into a flask containing about 100 cc of mixed acid -and then stand back. The rubber would swell and squirm for a moment, and then a magnificent rocket-like jet of flame would rise from the flask, with appropriate hissing noises. I could usually tell from the candidate's demeanor whether he had the sort of nervous system desirable in a propellant chemist.)"
I think it's a bimodal distribution. On the one hand you have the unflappable who just calmly watch what happens. On the other you have the far too flappable who is already out of the lab and making good time out of the building and the state.
Although for some reactions, the latter is the appropriate reaction.
Exactly this. Either they have the right stuff, or they don't.
Both are the right stuff.
I meant what was shown in this movie [0]. In a nutshell, the ability to remain calm when the unexpected happens, to try to solve the problem, or at least to not make it worse.
[0] https://en.m.wikipedia.org/wiki/The_Right_Stuff_(film)
[0] https://en.m.wikipedia.org/wiki/The_Right_Stuff_(film)
[deleted]
Ah so this is where the cartoon trope of jets of boiling fluid speeding up from a lab flask came from. I thought artists were exaggerating, but I guess not this time.
There was also a quote about chlorine trifluoride in Ignition!
”It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water-with which it reacts explosively. It can be kept in some of the ordinary structural metals-steel, copper, aluminium, etc.-because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminium keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.”
https://www.science.org/content/blog-post/sand-won-t-save-yo...
”It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water-with which it reacts explosively. It can be kept in some of the ordinary structural metals-steel, copper, aluminium, etc.-because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminium keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.”
https://www.science.org/content/blog-post/sand-won-t-save-yo...
There is an excellent YouTube channel that explains the V2 rocket in detail. Almost down to the last screw. Highly recommend. https://youtube.com/@RocketPlanet?si=DdgyQ8HFnswrZgZr
His videos about the Steam Pot [0] and the mechanical system that scheduled each stage of the rocket [1] are extremely good:
[0] https://www.youtube.com/watch?v=5C9xipCTe8I
[1] https://www.youtube.com/watch?v=lAFMl5bkP5Q
[0] https://www.youtube.com/watch?v=5C9xipCTe8I
[1] https://www.youtube.com/watch?v=lAFMl5bkP5Q
As a former chemist, I thought this book was a great example of "applied chemistry".
The theoretical aspects are challenging enough. But then you realize just how difficult the practical application of the theory can be. Sure, a mixture of fuming nitric acid and hydrazine will produce enough propulsion, but how do you dump tons of it into an engine without it just exploding?
The theoretical aspects are challenging enough. But then you realize just how difficult the practical application of the theory can be. Sure, a mixture of fuming nitric acid and hydrazine will produce enough propulsion, but how do you dump tons of it into an engine without it just exploding?
The section on building high-precision detonation speed timing apparatuses (and occasional explosive deconstruction of same) made me realize how uncomfortably close "information we require" and "catastrophic consequences of collection that information" are in the field.
There are few things that get certain types of chemists and engineers excited like being able to find out - and not being in trouble with ‘the bosses’ if it explodes a few times along the way.
Seconded! That is such a wonderful book.
Wouldn’t it be fascinating if there were an advanced civilization on a planet with gravity that was much higher than earth that couldn’t build chemical rockets and was therefore forced to build nuclear rockets?
What if that actually made the exploration of their solar system easier, since once they left the gravity well of their planet getting to other planets with nuclear rockets was comparatively trivial?
What if that actually made the exploration of their solar system easier, since once they left the gravity well of their planet getting to other planets with nuclear rockets was comparatively trivial?
These things are fun to imagine, but the real fun gets to be when you start talking about all the downstream effects. For example, if you can't build rockets you can't build GPS. Building a global communication system is much harder, which means things like shipping and flying are much more difficult. Not to mention that the gravity is much higher in the first place so flying is going to require way more fuel so how long does it take for them to get to that stage of civilization and how does their technological path differ? It gets even trickier once you start thinking about how the atmospheric composition will be different as gases follow similar escape velocities (e.g. Earth loses 3kg H/s but only 50g He/s) and it also determines what can even stay aloft. In general much of the technological paths are fairly straight forward, always iterating off of the current state (leaps and bounds are not common as they're more often a lack of domain expertise or not properly contextualized around the historical knowledge). But I think people forget how connected a lot of these things are. Then again, people often question why it is important that we build rockets, while asking those questions on their handheld computer connected to a global communication network. It's quite incredible how complex these interaction chains actually are and I think make you only admire the beautify of it all that much more.
Interestingly, development of rockets has only made a bunch of the things you mention cheaper (to the multiple orders of magnitude), not impossible.
Eg. determining location through radio signal triangulation can tell you a location pretty well, but would require placing a lot of signal stations throughout the world. Eg. remember the time-synchronisation mechanisms for watches through AM signals (including in hand watches).
Similarly, we did build a global communications network by placing expensive undersea cables across the world, but systems like StarLink are much cheaper (once you get to economies of scale for launching satellites).
So, like many things, rockets have accellerated discovery and progress, but are ultimately not the be-all solution: they work in tandem with the rest of science and engineering (including cultural development).
Eg. determining location through radio signal triangulation can tell you a location pretty well, but would require placing a lot of signal stations throughout the world. Eg. remember the time-synchronisation mechanisms for watches through AM signals (including in hand watches).
Similarly, we did build a global communications network by placing expensive undersea cables across the world, but systems like StarLink are much cheaper (once you get to economies of scale for launching satellites).
So, like many things, rockets have accellerated discovery and progress, but are ultimately not the be-all solution: they work in tandem with the rest of science and engineering (including cultural development).
GPS done via land radio systems would be so flakey and expensive it would still likely not be implemented. Easy to jam too. And subject to control by terrestrial authorities.
Putting a dozen satellites in orbit - and out of reach of local authorities - is so much cheaper and more reliable, it’s not just a matter of cost - it’s an entirely different product.
Same with starlink. A big part of its advantage is someone can’t just walk over and cut a cable. And no one needs planning approval to put a cable in.
Line of sight to low orbit is about the only way to accomplish that - maybe some kind of high altitude ballon/plane could (loon?) but they’re so comparatively easy to shoot down that it makes it a very different kind of situation.
Putting a dozen satellites in orbit - and out of reach of local authorities - is so much cheaper and more reliable, it’s not just a matter of cost - it’s an entirely different product.
Same with starlink. A big part of its advantage is someone can’t just walk over and cut a cable. And no one needs planning approval to put a cable in.
Line of sight to low orbit is about the only way to accomplish that - maybe some kind of high altitude ballon/plane could (loon?) but they’re so comparatively easy to shoot down that it makes it a very different kind of situation.
Yeah and to add to this I think people are forgetting why Bell was given a sanctioned monopoly. Because there were just cables everywhere. When people say natural monopolies exist in markets with network effects, that can mean literal networks of cables that will block out the sun. Sure, this stuff will improve too, but I think people are also forgetting about the increased surface area and the increased gravity which makes each of these cables required to be thicker or require more support.
https://history.stackexchange.com/questions/58872/did-they-r...
https://history.stackexchange.com/questions/58872/did-they-r...
It seems like you are looking at it only from one side.
Undersea cables are probably more expensive than satellites today, but we'll still continue to put them in. And nope, someone can't just walk in and cut a cable sitting at 5000m under the surface.
Detecting a StarLink terminal is relatively easy from the ground, and someone can just walk in and demolish it once they locate it.
Basically, all tech has pros and cons.
Undersea cables are probably more expensive than satellites today, but we'll still continue to put them in. And nope, someone can't just walk in and cut a cable sitting at 5000m under the surface.
Detecting a StarLink terminal is relatively easy from the ground, and someone can just walk in and demolish it once they locate it.
Basically, all tech has pros and cons.
Of course. But to Russias recent chagrin, blowing up/severing a fixed and very expensive cable (or underwater pipeline) is a generally far easier proposition than tracking down mobile and intermittent sources on the ground.
Still possible. But orders of magnitude harder. Nothing says that starlink ground station needs to stay in one place, after all.
Undersea cables get cut all the time, from shipping to nation states.
Trains don’t make cars obsolete, anymore than cars make trains obsolete. Taking out train tracks is much easier and more effective than taking out all possible roads though.
Still possible. But orders of magnitude harder. Nothing says that starlink ground station needs to stay in one place, after all.
Undersea cables get cut all the time, from shipping to nation states.
Trains don’t make cars obsolete, anymore than cars make trains obsolete. Taking out train tracks is much easier and more effective than taking out all possible roads though.
> Undersea cables are probably more expensive than satellites today, but we'll still continue to put them in. And nope, someone can't just walk in and cut a cable sitting at 5000m under the surface.
The cable has to come out on to the surface somewhere, though.
But barring that, dropping IEDs from a fishing boat, with a time fuse and some weight, isn't hard; the trickier part would be knowing where to drop them so they land near the cable. But there are tricks for that too.
The cable has to come out on to the surface somewhere, though.
But barring that, dropping IEDs from a fishing boat, with a time fuse and some weight, isn't hard; the trickier part would be knowing where to drop them so they land near the cable. But there are tricks for that too.
You might be surprised to learn that Enhanced LORAN recently became operational around the UK's coast, specifically because satellite-based PNT is so susceptible to interference and jamming.
Not at all. It's only being installed in specific, high value areas within a specific jurisdiction. And mainly as a backup. Notably by a party which doesn't control GPS (albeit a close ally).
LORAN has also been used near airports in developed areas for a long time.
That isn't the 'base case' though.
The US military initially developed and launched GPS because of the reasons I stated, and it is still widely used as a base case for exactly those reasons.
LORAN has also been used near airports in developed areas for a long time.
That isn't the 'base case' though.
The US military initially developed and launched GPS because of the reasons I stated, and it is still widely used as a base case for exactly those reasons.
> Interestingly, development of rockets has only made a bunch of the things you mention cheaper (to the multiple orders of magnitude), not impossible.
With finite time, lifespan and resources, "cheap" is often equivalent to "possible". If you look at the connections between inventions and developments that GP mentioned, it's usually the case that the necessary prerequisites don't involve just knowledge, but something getting cheap enough to be available / worth building.
With finite time, lifespan and resources, "cheap" is often equivalent to "possible". If you look at the connections between inventions and developments that GP mentioned, it's usually the case that the necessary prerequisites don't involve just knowledge, but something getting cheap enough to be available / worth building.
If something is worthwhile, it gets developed and gradually becomes cheaper.
If you were handed an internal combustion engine car without petrol, it would be extremely expensive to get that fuel for the first time.
That even happened with satellites!
If you were handed an internal combustion engine car without petrol, it would be extremely expensive to get that fuel for the first time.
That even happened with satellites!
Which actually leads me to thinking that a space-adapted race really doesn't want to bother with planets and their big ass gravity well.
Resource extraction from asteroids or moons is a lot easier than carting it out of a big gravity well. Building stations in zero G rather than having to worry about orbital degradation and the like. Atmospheres get in the way of solar energy collection.
Earth is probably only useful as a vacation destination. Unless of course all those UFO reports are actual physics-defying antigrav drives with little green men.
Resource extraction from asteroids or moons is a lot easier than carting it out of a big gravity well. Building stations in zero G rather than having to worry about orbital degradation and the like. Atmospheres get in the way of solar energy collection.
Earth is probably only useful as a vacation destination. Unless of course all those UFO reports are actual physics-defying antigrav drives with little green men.
The nice thing about gravity wells is they naturally concentrate things along density gradients.
The bad thing about gravity wells is they naturally concentrate things along density gradients.
The bad thing about gravity wells is they naturally concentrate things along density gradients.
Interesting thought. I think ground-based GPS wouldn't be too difficult though - we already have most of earth covered by GSM/3G/LTE, and with updated towers you could have something as precise, if not more, as GPS. Of course the coverage wouldn't be 100%, and navigating in ocean would be more difficult.
Planes would be replaced by trains and aquaplanes for sure. Our modern fastest trains (TGV, Maglev) are only half as slow as the fastest commercial planes. Also, you might have rocketry on such a planet, just not for orbit, and for things that right now we use jets for.
The biggest issue with be probably no detailed aerial maps, and in later stages - no space mining, so such civilisation would be limited to resources on their own planet.
Also, I'm imagining that such a civilisation would send out more signals into space to encourage someone to come and visit them, and hopefully dropship resources from orbit :D
Imagine two civilisations living like that in symbiosis - one on the orbit, able to drop things to the one that is lower, but being able to extract only information / art / mental labour / energy from below.
Planes would be replaced by trains and aquaplanes for sure. Our modern fastest trains (TGV, Maglev) are only half as slow as the fastest commercial planes. Also, you might have rocketry on such a planet, just not for orbit, and for things that right now we use jets for.
The biggest issue with be probably no detailed aerial maps, and in later stages - no space mining, so such civilisation would be limited to resources on their own planet.
Also, I'm imagining that such a civilisation would send out more signals into space to encourage someone to come and visit them, and hopefully dropship resources from orbit :D
Imagine two civilisations living like that in symbiosis - one on the orbit, able to drop things to the one that is lower, but being able to extract only information / art / mental labour / energy from below.
Higher gravity -> denser atmosphere -> airships start making more sense? In those conditions, flying could've been actually cheaper and safer, even though slower than what we have on our planet.
If you could get to space with a fusion engine, then why would taking satellites into space on said rocket be any different then it is for us (to build GPS)?
Wouldn't LTA blimps work BETTER in higher gravity for flying?
Wouldn't LTA blimps work BETTER in higher gravity for flying?
A limit often ignored for high-gravity balloons is, the pressure gradient inside the balloon reaches a point where it tears it apart. When the atmospheric gradient is compressed to some point, the distance between the bottom of the balloon and the top can create enormous forces on the fabric.
So depending on the gravity we're talking about, blimps are out!
So depending on the gravity we're talking about, blimps are out!
That civilization could have invested in rail transit and tunneling instead. Positioning isn’t so hard on fixed roads, although fixing the, in the first place under oceans could be a problem. They might figure out triangulation using their planet’s magnetic field or something. It’s also completely possible that life isn’t viable at all on non-Earth like planets.
Remember that the gravity is higher. Your mountains are more dense and your oceans have more pressure. You're not living on a world with 14psi. You're not living in a world with the same ground, air, or ocean composition. All these change. So all your drills have to be thicker and harder. All your cables need to be stronger.
All projectiles become much shorter range weapons. Maybe once they've got gunpowder they can finally fight at range, though each shot would require a lot more gunpowder relative to the same shot on earth. Maybe it sort of washes out if you figure the inhabitants are all stronger and more sturdy as a result of the gravity.
Such an effect may even highly discourage ranged combat in the first place. I'm sure you'd still have ballista but bows? Probably crossbows. But there's definitely a butterfly effect for sure.
It feels like we've finally found a reason for the old sci-fi trope of future battles using melee weapons
I'm wondering if siege weapons work at all
I'm wondering if siege weapons work at all
Dune has a take on this that the movie doesn't do a great job at explaining. But the shield is made to prevent high velocity projectiles and energy weapons. This way the shield can be hidden and fool enemies because the user is still able to interact with daily objects. Like you can eat while wearing the shield and since you'd have body guards it's much harder to get in and stab someone wearing a shield. The Apple version of Foundation has a similar shield but it is more sensitive. Dune's shield has obviously affected many subsequent works.
> once they left the gravity well of their planet getting to other planets with nuclear rockets was comparatively trivial?
We are actually on that planet. Spacecraft have what is called delta-v, which is basically a measure of what orbit changes they can perform given the amount of fuel they have onboard. For example getting from the ground to LEO has one measure, and getting from LEO to moon orbit has another.
It varies somewhat by the specific rocket to get into space (due to drag and effects of higher gravity), but once you are there it's basically the same for all spaceships.
It takes around 9.6km/s (no relation to gravity, just a coincidence) of delta-v to get into LEO, however once you are there it's fairly cheap to get around the solar system. To get from Earth LEO to a captured orbit around Mars needs a delta-v of around 5km/s - yes, less than to get into Earth orbit. To get out further to Neptune would need around 12km/s of delta-v.
We are actually on that planet. Spacecraft have what is called delta-v, which is basically a measure of what orbit changes they can perform given the amount of fuel they have onboard. For example getting from the ground to LEO has one measure, and getting from LEO to moon orbit has another.
It varies somewhat by the specific rocket to get into space (due to drag and effects of higher gravity), but once you are there it's basically the same for all spaceships.
It takes around 9.6km/s (no relation to gravity, just a coincidence) of delta-v to get into LEO, however once you are there it's fairly cheap to get around the solar system. To get from Earth LEO to a captured orbit around Mars needs a delta-v of around 5km/s - yes, less than to get into Earth orbit. To get out further to Neptune would need around 12km/s of delta-v.
Oddly enough nuclear rockets aren't particularly powerful and tend to be extremely heavy. Their strength is that they're highly efficient, so they can just keep going with relatively little fuel. Chemical rockets, by contrast, tend to be extremely high power but also extremely inefficient. Here's a few comparisons:
----
NERVA [1] / Nuclear / 1969 / 246kN thrust / 18,000 kg mass, 841s ISP (seconds of specific impulse - higher is better/more efficient, a little is a lot) / The only completed possibly launch viable nuclear rocket engine, as far as I know.
F-1 [2] / Chemical / 1959 / 7,770kN thrust, 8,400 kg mass, 263s ISP / Powered the Apollo rockets
Merlin [3] / Chemical / 2007 / 981kN thrust, 470 kg mass, 282s ISP / Powers the SpaceX Falcon 9 in a group of 9
Raptor [4] / Chemical / ?? / 2,640kN thrust, 1,600 kg mass / 327s ISP / Powers the SpaceX Starship in a group of 33
----
So what really matters in a rocket, for getting off Earth, is its thrust to weight ratio. NERVA isn't inefficient because it's dated (which was part of the reason I included the F-1), but simply because nuclear itself has an inherently poor thrust to weight ratio. However it just keeps going and going and going, which makes it absolutely awesome for travel once you're already in space.
It's even "fast" in space, because of how travel in space works. You don't just keep thrusting in space; instead you make a limited burn and then coast to where you're going, making a final reversal burn towards the end. So even if it takes hundreds of times as as long to reach a higher cruising velocity, it'll end up getting to the destination long before a chemical rocket, for any sufficiently distant destination.
----
[1] - https://en.wikipedia.org/wiki/NERVA
[2] - https://en.wikipedia.org/wiki/Rocketdyne_F-1
[3] - https://en.wikipedia.org/wiki/SpaceX_Merlin
[4] - https://en.wikipedia.org/wiki/SpaceX_Starship
----
NERVA [1] / Nuclear / 1969 / 246kN thrust / 18,000 kg mass, 841s ISP (seconds of specific impulse - higher is better/more efficient, a little is a lot) / The only completed possibly launch viable nuclear rocket engine, as far as I know.
F-1 [2] / Chemical / 1959 / 7,770kN thrust, 8,400 kg mass, 263s ISP / Powered the Apollo rockets
Merlin [3] / Chemical / 2007 / 981kN thrust, 470 kg mass, 282s ISP / Powers the SpaceX Falcon 9 in a group of 9
Raptor [4] / Chemical / ?? / 2,640kN thrust, 1,600 kg mass / 327s ISP / Powers the SpaceX Starship in a group of 33
----
So what really matters in a rocket, for getting off Earth, is its thrust to weight ratio. NERVA isn't inefficient because it's dated (which was part of the reason I included the F-1), but simply because nuclear itself has an inherently poor thrust to weight ratio. However it just keeps going and going and going, which makes it absolutely awesome for travel once you're already in space.
It's even "fast" in space, because of how travel in space works. You don't just keep thrusting in space; instead you make a limited burn and then coast to where you're going, making a final reversal burn towards the end. So even if it takes hundreds of times as as long to reach a higher cruising velocity, it'll end up getting to the destination long before a chemical rocket, for any sufficiently distant destination.
----
[1] - https://en.wikipedia.org/wiki/NERVA
[2] - https://en.wikipedia.org/wiki/Rocketdyne_F-1
[3] - https://en.wikipedia.org/wiki/SpaceX_Merlin
[4] - https://en.wikipedia.org/wiki/SpaceX_Starship
> It's even "fast" in space, because of how travel in space works. You don't just keep thrusting in space; instead you make a limited burn and then coast to where you're going, making a final reversal burn towards the end.
The dream of course is that you keep thrusting, accelerating until the halfway point, then flip around and burn to decelerate. In that scheme, your thrust doubles as artificial gravity too!
The dream of course is that you keep thrusting, accelerating until the halfway point, then flip around and burn to decelerate. In that scheme, your thrust doubles as artificial gravity too!
> we lived on a planet where gravity and chemistry would make orbital rockets possible
It's kind of insane luck. Bit heavier planet and we wouldn't be able to have a single satellite before building nuclear engines.
It's kind of insane luck. Bit heavier planet and we wouldn't be able to have a single satellite before building nuclear engines.
I'm not sure how nuclear engines would help?
A nuclear reactor is a bit like an ion drive: great for long distance space travel, but not great for getting off a planet.
Unless you mean the kind of nuclear engine that consists of detonating atomic bombs behind you? See https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
A nuclear reactor is a bit like an ion drive: great for long distance space travel, but not great for getting off a planet.
Unless you mean the kind of nuclear engine that consists of detonating atomic bombs behind you? See https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
For non-manned launches and those that can be hardened to withstand extraordinary g-force, something akin to setup that resulted in the missing (900 kg) borehole cap of Operation Plumbbob may do the trick.
Acceleration to 66 km/s is probably a little bit overkill, even.
https://en.m.wikipedia.org/wiki/Operation_Plumbbob
Acceleration to 66 km/s is probably a little bit overkill, even.
https://en.m.wikipedia.org/wiki/Operation_Plumbbob
Orion drive should work fine.
Thrust to weight of a nuclear engine is fairly poor, so they are best suited for upper stage or in-space work. A heavy-planet rocket might use chemical propulsion in a lower stage just like we do and a high-energy nuclear upper stage (or two) where the really high Isp would be quite useful.
> A nuclear reactor is a bit like an ion drive: great for long distance space travel, but not great for getting off a planet.
What are you basing this on? NERVA was for getting off the planet. It had a thrust of ~250 kN. In comparison, a SpaceX Merlin engine has a thrust of ~900 kN, while ion drives have <1 N of thrust.
What are you basing this on? NERVA was for getting off the planet. It had a thrust of ~250 kN. In comparison, a SpaceX Merlin engine has a thrust of ~900 kN, while ion drives have <1 N of thrust.
High fixed (non propellant) drive weight compared to chemical rockets makes it pretty inefficient due to the gravity well - thrust/weight ratio vs time matters a lot when you’re quickly climbing out of the well. And it is very difficult to do that quickly with nuclear without exceeding our materials science abilities and causing a nuclear accident.
Additionally, atmospheric density and friction matter a lot in these situations, and getting out of high density atmosphere and ‘up’ as quickly as possible pays large dividends.
Maybe something like NERVA
If you have a sufficiently tall* first stage, and use hot staging, then you can make it work on even on an extremely large Earth.**
*First stage may need to extend well above the atmosphere.
**No, that's for-sure not a Randall Munroe book in my hand.
*First stage may need to extend well above the atmosphere.
**No, that's for-sure not a Randall Munroe book in my hand.
This is the same way you make a train capable of traveling from Los Angeles to New York in 1 second. A sufficiently long train.
I think the speed of sound in steel (or whatever the train is made out of) is slower than that.
But I guess you could cheat by having multiple engines along the way that all accelerate in lockstep.
But I guess you could cheat by having multiple engines along the way that all accelerate in lockstep.
Or you could just put the engine in the front. There's no rule a train can't arrive before leaving after all.
Related theoretical question for those who are of the physics mindset - if I had a long (very long like 1 light minute long) bar of metal and I pushed on one end, I'm assuming the other end would not move instantaneously because that would imply some part somewhere inside the bar was moving faster than the speed of light. So I'm assuming that the bar would just compress slightly and for a period of time in between when I pushed on one end and when the other end moved the bar would be slightly shorter. That's fine if that's the case.
But what if the thing I push on is a quantum particle? Does this same thing happen at the smallest scales? If one end of a quark is pushed on does the other end move instantaneously or is there a small(!) delay?
Probably the answer is just "that's not how quarks work" but I've always been curious.
But what if the thing I push on is a quantum particle? Does this same thing happen at the smallest scales? If one end of a quark is pushed on does the other end move instantaneously or is there a small(!) delay?
Probably the answer is just "that's not how quarks work" but I've always been curious.
There's no such thing as instantenously "pushing" on a particle. E.g. electrons can be accelerated by electromagnetic fields. If the field changes, the electron feels a force and is accelerated according to a = F/m (handwaving away relativity). When you macroscopically push against a rigid body, what happens at the particle level is your constituent atoms' electrons (and protons) interact with each other through the electromagnetic field.
The other answers are correct that it's an acoustic wave, but sometimes it helps to see a demo "proving" it:
https://youtu.be/DqhXsEgLMJ0
https://youtu.be/DqhXsEgLMJ0
When you tap on the bar it creates an acoustic wave that will propagate at the speed of sound in the material.
For subatomic particles, the most intuitive way to think about things is to adopt the "fields are real" mindset. Here fields are the underlying reality, and particles are just a pattern of waves excited in the fields. Disturbances in all fundamental fields we've discovered propagate at the speed of light, and we have pretty solid reasons for believing no future discovery will contradict that, as it would break causality in a fundamental way.
For subatomic particles, the most intuitive way to think about things is to adopt the "fields are real" mindset. Here fields are the underlying reality, and particles are just a pattern of waves excited in the fields. Disturbances in all fundamental fields we've discovered propagate at the speed of light, and we have pretty solid reasons for believing no future discovery will contradict that, as it would break causality in a fundamental way.
> If one end of a quark is pushed on does the other end move instantaneously
Quarks don't have an "other end." To the best of our knowledge, particles are points.
Quarks don't have an "other end." To the best of our knowledge, particles are points.
On your long bar, the push propagates at the speed of sound in the material. Look up Slinky drops on YouTube.
Interactions between particles such as quarks are mediated by fields filling the space between them (such as electromagnetic field and gluon field). Ripples in these fields propagate at speed less than or equal to c.
This is a classical picture, but the quantum picture is similar: evolution is generated by a local Hamiltonian constructed out of field operators attached to every point of space.
So, both classically and quantumly, relativity demands the existence of fields filling space to propagate causal influences at finite speed.
This is a classical picture, but the quantum picture is similar: evolution is generated by a local Hamiltonian constructed out of field operators attached to every point of space.
So, both classically and quantumly, relativity demands the existence of fields filling space to propagate causal influences at finite speed.
"Speed of light" makes more intuitive sense when you think of it more as the speed of causality i.e. the fastest physical speed a cause can have an effect
The speed of light in a vacuum happens to be the best representation of the maximum speed of causality
Which also makes more sense why you can't do things like travel faster than light (your effect would precede the cause), and why two protons going past each other in opposite directions don't violate this law
The speed of light in a vacuum happens to be the best representation of the maximum speed of causality
Which also makes more sense why you can't do things like travel faster than light (your effect would precede the cause), and why two protons going past each other in opposite directions don't violate this law
Surely for a train to "travel" from LA to NY, it "starts" when the front of the vehicle passes a line in LA, and "finishes" when the front of the vehicle crosses a line in NY.
Just build two fronts. The Germans did it with their ICE trains.
I’m trying to decide whether you’re describing a rocket or a space elevator. If you build a tower that extends to somewhere near geostationary orbit, you can pretend it’s a rocket stage delivering a delta V of zero, and you can “hot stage” a tiny little stage off the top, and voila, you’re in orbit.
Of course, once you’ve managed to build this, the rockets are basically optional. :)
Of course, once you’ve managed to build this, the rockets are basically optional. :)
You’re going to have a hell of a difficult time trying to construct anything that tall on a high-g planet. The taper ratio between the base and the top would have to be enormous – likely a sizeable fraction of the radius of the planet! Though I guess it would have to be anyway so you have somewhere to attach all those first-stage engines…
If you're allowed to build it tall enough, just don't even light the first stages. Launch the final stage directly from a high enough altitude that it can escape on its own.
Well, yeah, but building something tall enough to reach the synchronous orbit is impossible even on Earth, there’s no material with even a thousandth of the compressive strength required. Space elevators are only possible because they’re tensile structures and the “bottom” that supports the weight of the entire structure is up there in a low gee environment.
Remember that just getting outside the atmosphere is the almost trivial part of rocketry compared to the problem of having to then accelerate to >= orbital speed fast enough to not fall down!
And anyway you’d have to dismantle the planet to build your launch tower, which I guess would solve your problem, in a fashion. Though – whatever you turned your planet into would just have an annoying tendency to rapidly collapse back into a ball.
Remember that just getting outside the atmosphere is the almost trivial part of rocketry compared to the problem of having to then accelerate to >= orbital speed fast enough to not fall down!
And anyway you’d have to dismantle the planet to build your launch tower, which I guess would solve your problem, in a fashion. Though – whatever you turned your planet into would just have an annoying tendency to rapidly collapse back into a ball.
If you really have a lot of time for the project (starting early in the star's burn?), you might try using photovoltaics to move a lot of mass across the surface to ahead of where tides would accumulate, slowly speeding up the day/night cycle. The faster you spin, the flatter your geoid and you should probably stop accelerating before your entire equator region goes interplanetary.
On earth, you could use active support to build your tall structures, then you don't need exotic super-materials. See eg https://en.wikipedia.org/wiki/Space_fountain
You just need to launch off of the highest point on the planet! (Kerbal Space Program approved).
We don't talk about ground logistics though.
We don't talk about ground logistics though.
** And assuming sufficient propellant exists on your planet :)
You could just perch the first stage at the top of a sufficiently tall mountain.
Could, but at least on Earth the difficulties outweigh the gains enough to make it too expensive. https://youtu.be/4m75t4x1V2o?si=6FzbQYrLtl7Zfe0J&t=157
Fascinating. This may weigh down the Drake equation, particularly in reducing the average time civilizations survive on planets with high gravity because their ability to become multiplanetary and survive great filters is limited.
One of the biggest hypothetical great filters is massive war. Higher engineering requirements for rockets (or even simple projectiles such as cannons or arrows) would set limits on the rate of increase of warfare technology. It's possible other means of diplomacy would advance at sufficient speed to preempt population annihilation from global war.
I'm curious what effect an increase of gravity may have on heavier-than-water displacement craft (canoes and other modern boats). I think probably none, since you're dealing with density, not weight. Except for any increase in density of early building materials and cargo/supercargo. But it's been long enough from physics I'm unsure.
I think atmospheric density is more dependent on magnetic field than gravity.
I'm curious what effect an increase of gravity may have on heavier-than-water displacement craft (canoes and other modern boats). I think probably none, since you're dealing with density, not weight. Except for any increase in density of early building materials and cargo/supercargo. But it's been long enough from physics I'm unsure.
I think atmospheric density is more dependent on magnetic field than gravity.
The thing I often think about is while the demands for an orbital class vehicle quickly become untenable, ICBM's stay viable for a lot longer. I don't know if MAD is more or less stable without the prospect of space exploration.
I would argue that situation is usually more stable with less secrecy, so a lack of spy satellites would not be beneficial.
Absence of comm satellites would also help fragment the world and make the idea of a surprise attacks more enticing.
Absence of comm satellites would also help fragment the world and make the idea of a surprise attacks more enticing.
Not beneficial, but I imagine you’d just see a lot more spyplanes.
Spy planes can be shot from the ground, or with another plane. This is closer to an act of hot war :(
Orbital space (around modern Earth) is ex-territorial, so killing a spy satellite would be seen as an act of aggression, not legitimate defense. This holds back "kinetic action" in near-Earth space.
Orbital space (around modern Earth) is ex-territorial, so killing a spy satellite would be seen as an act of aggression, not legitimate defense. This holds back "kinetic action" in near-Earth space.
> Orbital space (around modern Earth) is ex-territorial, [...]
That's a historical accident of arrangements on earth (so less useful in the Fermi-paradox / filter debate), and could easily have gone differently. Ie air space could also have been seen as ex-territorial.
That's a historical accident of arrangements on earth (so less useful in the Fermi-paradox / filter debate), and could easily have gone differently. Ie air space could also have been seen as ex-territorial.
Assuming something like air space territories in these other cultures, extending them out to infinity seems... tricky. Wouldn't it imply that the ownership of various celestial bodies changes with time?
My recollection of how it evolved on Earth was the soviet's more asked forgiveness than permission and eisenhower basically shrugged and said "whatever, at least our spy satellites can go over you too"
My recollection of how it evolved on Earth was the soviet's more asked forgiveness than permission and eisenhower basically shrugged and said "whatever, at least our spy satellites can go over you too"
We can make certain assumptions guided by game theory and ideas about evolution to speculate what aliens might or might not do.
See also how for us earthlings the moon is considered the common property of all mankind or something like that. And that's all well and good as long as no one can actually reach it well enough to make use of it; but I predict as soon as we have useful moonbases, we will move to a conception that's closer to 'possession is nine tenth of the law', if not outright 'might makes right'.
If not de-jure, then definitely at least de-facto.
See also how for us earthlings the moon is considered the common property of all mankind or something like that. And that's all well and good as long as no one can actually reach it well enough to make use of it; but I predict as soon as we have useful moonbases, we will move to a conception that's closer to 'possession is nine tenth of the law', if not outright 'might makes right'.
If not de-jure, then definitely at least de-facto.
War may be the exception, not the rule.
Just because we're built for it doesn't mean other species will be.
If evolving in a different environment, they might be built for cooperation. That is, in a certain environment the only species that can evolve enough to go interplanetary might be a species that learned to co-exist internally and externally, otherwise the environment would have kept them down.
Just because we're built for it doesn't mean other species will be.
If evolving in a different environment, they might be built for cooperation. That is, in a certain environment the only species that can evolve enough to go interplanetary might be a species that learned to co-exist internally and externally, otherwise the environment would have kept them down.
> War may be the exception, not the rule.
> Just because we're built for it doesn't mean other species will be.
You heard of what chimps get up to? Ants? Microbes? They don't just have wars; They have raiding parties, take slaves, serve as battlefield medics, compete in intrafactional and interfactional rivalries that slowly boil over… Hell, even trees actively release toxins to try to kill other nearby plants.
On a long enough timescale, war is almost certainly highly (and lethally) maladaptive.
But in a non-post-scarcity environment with social contact, creatures whose bodies disagree with entropy tend to learn that violence is an effective tactic for taking others' calories/oil and nutrients/minerals.
Maybe there's exceptions. I hope so, anyway.
> Just because we're built for it doesn't mean other species will be.
You heard of what chimps get up to? Ants? Microbes? They don't just have wars; They have raiding parties, take slaves, serve as battlefield medics, compete in intrafactional and interfactional rivalries that slowly boil over… Hell, even trees actively release toxins to try to kill other nearby plants.
On a long enough timescale, war is almost certainly highly (and lethally) maladaptive.
But in a non-post-scarcity environment with social contact, creatures whose bodies disagree with entropy tend to learn that violence is an effective tactic for taking others' calories/oil and nutrients/minerals.
Maybe there's exceptions. I hope so, anyway.
All those species evolved on the same planet, with the same constraints.
War works well for them, so they evolved to get better and better at it.
But war is resource-intensive and costs lives. Lives are easily replaced on Earth.
It’s not hard to imagine a planet where going to war would be mutually assured destruction on a species level, even for ants and microbes.
War works well for them, so they evolved to get better and better at it.
But war is resource-intensive and costs lives. Lives are easily replaced on Earth.
It’s not hard to imagine a planet where going to war would be mutually assured destruction on a species level, even for ants and microbes.
> It’s not hard to imagine a planet where going to war would be mutually assured destruction on a species level, even for ants and microbes.
That is very hard to imagine, how do you reckon that would be possible? Does the planet only support a couple of anthills and then all resources are consumed? How would ants even appear on such a planet?
That is very hard to imagine, how do you reckon that would be possible? Does the planet only support a couple of anthills and then all resources are consumed? How would ants even appear on such a planet?
Interesting thought, but how would that work?
If the environment is so hostile that life keeps appearing, failing to find a foothold, then getting crushed by statistics, then if some resilient life does eventually develop, it might be able to survive in such a hostile environment only through internal/external cooperation or symbiosis.
For instance, if two or more extremophiles evolved together but remained separate species. They might even require one another’s contribution to successfully procreate. And successful procreation might be rare.
That sort of life, if it evolved to consciousness, would be averse to any form of damaging competition.
One poorly timed selfish move and the hostile environment wins: everybody dies.
This cooperation imperative would be built into their biochemistry, same as war is built into ours.
You’d probably still find insane or outlier members of their society, who are radically uncooperative or individualistic. But they would be rare and containable, otherwise their species couldn’t exist.
For instance, if two or more extremophiles evolved together but remained separate species. They might even require one another’s contribution to successfully procreate. And successful procreation might be rare.
That sort of life, if it evolved to consciousness, would be averse to any form of damaging competition.
One poorly timed selfish move and the hostile environment wins: everybody dies.
This cooperation imperative would be built into their biochemistry, same as war is built into ours.
You’d probably still find insane or outlier members of their society, who are radically uncooperative or individualistic. But they would be rare and containable, otherwise their species couldn’t exist.
> For instance, if two or more extremophiles evolved together but remained separate species. They might even require one another’s contribution to successfully procreate. And successful procreation might be rare.
> That sort of life, if it evolved to consciousness, would be averse to any form of damaging competition.
Uh. That sounds like us. Our dependence on our mitochondria and chloroplasts to survive as microbial life, it turns out, did not translate into an aversion to war after we grew up as macroscopic life and everybody around us had their own endosymbionts too.
Honestly I think you're going in the wrong direction with this. A crueler world results in crueler people; scarcity begets conflict. Maybe you could technically create peace by simpy isolating everybody in some kind of desert-like environment, but if you want a Nash equilibrium and selection pressures favouring active prosocial cooperation, then I think what our own history of war, domestication, self-domestication, democratization, etc. shows is that you effectively need (amongst other things) an almost post-scarcity environment, where basic physical resources are no longer a constantly urgent limiting factor on life— A techno-utopia with nuclear weapons and additive manufacturing has both much more to gain from cooperation and much more to lose from war than their less fortunate equivalent struggling just to survive.
But then that goes back to my original reply to you: Anybody who evolves through that initial awkward phase of competition in fear of entropy is probably going to have violence as a part of that history, and part of themselves.
---
Note that effectively post-scarcity environments do actually appear in nature now and then, and when they do appear, they do sometimes result in apparently utopic, peaceful, and more empathetic societies. E.g. for a particularly stark example, see bonobos versus chimps.
But as with many good things, it seems to usually be highly spacially/socially local, and temporally transient.
> That sort of life, if it evolved to consciousness, would be averse to any form of damaging competition.
Uh. That sounds like us. Our dependence on our mitochondria and chloroplasts to survive as microbial life, it turns out, did not translate into an aversion to war after we grew up as macroscopic life and everybody around us had their own endosymbionts too.
Honestly I think you're going in the wrong direction with this. A crueler world results in crueler people; scarcity begets conflict. Maybe you could technically create peace by simpy isolating everybody in some kind of desert-like environment, but if you want a Nash equilibrium and selection pressures favouring active prosocial cooperation, then I think what our own history of war, domestication, self-domestication, democratization, etc. shows is that you effectively need (amongst other things) an almost post-scarcity environment, where basic physical resources are no longer a constantly urgent limiting factor on life— A techno-utopia with nuclear weapons and additive manufacturing has both much more to gain from cooperation and much more to lose from war than their less fortunate equivalent struggling just to survive.
But then that goes back to my original reply to you: Anybody who evolves through that initial awkward phase of competition in fear of entropy is probably going to have violence as a part of that history, and part of themselves.
---
Note that effectively post-scarcity environments do actually appear in nature now and then, and when they do appear, they do sometimes result in apparently utopic, peaceful, and more empathetic societies. E.g. for a particularly stark example, see bonobos versus chimps.
But as with many good things, it seems to usually be highly spacially/socially local, and temporally transient.
We evolved in an environment in which competition is non-lethal and beneficial.
Other environments may differ.
Other environments may differ.
....Could be something like extremophilic archaea here on Earth? Not sure how they treat each other, but they're usually quite friendly (beneficial, or harmless— never pathogenic or parasitic) to us mammals– Something about branched separation in biochemistry and highly diverse ecological niches making resource competition less of a thing, I'd guess.
But that's not really "mutually assured destruction on a species level", so much as more to gain by working together– Which honestly is better.
But that's not really "mutually assured destruction on a species level", so much as more to gain by working together– Which honestly is better.
>I think atmospheric density is more dependent on magnetic field than gravity.
Atmospheric density is very much affected by gravity. I'm not sure magnetic field has any appreciable effect at all on the density of the earth's atmosphere. Why would it? The vast majority of the atmosphere isn't charged, so doesn't interact directly with magnetism.
Atmospheric density is very much affected by gravity. I'm not sure magnetic field has any appreciable effect at all on the density of the earth's atmosphere. Why would it? The vast majority of the atmosphere isn't charged, so doesn't interact directly with magnetism.
Magnetic field protects from solar wind that strips atmosphere.
It's often said but with heavy evidence to yhr contrary e.g. Venus. Venue's negligible magnetic field is almost non-existent yet its atmosphere is many many times thicker than ours.
In fact, earth actively loses material to space because is has a magnetosphere, polar outflow of oxygen for example.
Venus loses a lot of material, too.
One of the reasons Venus still has a dense atmosphere is because its atmosphere is mostly composed of a relatively heavy compound, CO2, which is harder to lose than lighter gases like H2, N2, and O2.
One of the reasons Venus still has a dense atmosphere is because its atmosphere is mostly composed of a relatively heavy compound, CO2, which is harder to lose than lighter gases like H2, N2, and O2.
If you turned off the earth's magnetic field today, then presumably the atmosphere would be gradually stripped, away over millions of years. Similar to what happened to Mars. But it would not make any immediate difference to the density.
Not immediate, no.
But magnetic fields don't usually just switch off. If the planet didn't have one to begin with, then it probably doesn't have much of an atmosphere for long enough for advanced life.
But magnetic fields don't usually just switch off. If the planet didn't have one to begin with, then it probably doesn't have much of an atmosphere for long enough for advanced life.
Buoyancy is indeed not affected by gravity, you're correct.
Depends how compressible the fluid you're floating in is right? Note that's 'fluid' rather than just liquid.
As you increase gravity, with fully compressible fluids the buoyancy scales the same as weight, you wouldn't sink lower. But with any incompressibilty you'd need to displace proportionally more (ie sink down more) to counter the increasing weight.
(I think)
As you increase gravity, with fully compressible fluids the buoyancy scales the same as weight, you wouldn't sink lower. But with any incompressibilty you'd need to displace proportionally more (ie sink down more) to counter the increasing weight.
(I think)
> But with any incompressibilty you'd need to displace proportionally more (ie sink down more) to counter the increasing weight.
The water would also weigh more. Buoyancy is the force of the water around the volume you displaced being pulled down into that space, exerting pressure that pushes you up. So you'd float just as well.
Actually, the compressible fluids would become denser, and make it easier for you to float (assuming you're relatively incompressible). At the extreme end, you could swim in pressure-liquified air (assuming you survive being crushed, of course).
The water would also weigh more. Buoyancy is the force of the water around the volume you displaced being pulled down into that space, exerting pressure that pushes you up. So you'd float just as well.
Actually, the compressible fluids would become denser, and make it easier for you to float (assuming you're relatively incompressible). At the extreme end, you could swim in pressure-liquified air (assuming you survive being crushed, of course).
This is technically wrong. Increase in gravity does affect buoyancy because air density changes with gravity. The reason is that the column of air above you is compressed by gravity. With very large gravity, all the atmosphere could be compressed down to possibly a few km.
Replies are accurate (more precise?), it is more true to say that buoyancy in a virtually incompressible liquid is not affected by gravity because even if gravity is increased, the water experiences it the same as the buoyant mass.
If you can't shoot them, surely you can keep stabbing them until you develop bio-warfare? Then you can both go extinct and the filter keeps working.
You may find the concept of Superhabitabilty interesting.
The hypothesis suggests that larger planets with more mass and gravity than Earth would be more favorable to life. It’s certainly possible that there is a lot more life out there on planets where getting into space is nearly impossible with conventional chemical rockets.
We may be living on a comparatively barren rock, but the tradeoff of that we are actually able to get into orbit.
https://en.wikipedia.org/wiki/Superhabitable_planet
The hypothesis suggests that larger planets with more mass and gravity than Earth would be more favorable to life. It’s certainly possible that there is a lot more life out there on planets where getting into space is nearly impossible with conventional chemical rockets.
We may be living on a comparatively barren rock, but the tradeoff of that we are actually able to get into orbit.
https://en.wikipedia.org/wiki/Superhabitable_planet
Imagine visiting such planet. They'd think you are gods because, how did you get up there? But you can't really land because it would be one way trip for your tech.
So you just hang around and talk with radiowaves, sending them pictures of their world from above they could never see otherwise.
So you just hang around and talk with radiowaves, sending them pictures of their world from above they could never see otherwise.
If you have the power to cross the stars, surely taking off from a steep gravity well wouldn't be a problem.
But I do like the idea that you wouldn't be able to.
So instead you slingshot your orbital craft past the planet, using its gravity well itself to build up speed— And you release a cable ahead of you, that swings down through the atmosphere to zero surface velocity at the point of your perigee, so your away team and their new friends can attach it to a glass elevator and be smoothly hoisted into space.
But I do like the idea that you wouldn't be able to.
So instead you slingshot your orbital craft past the planet, using its gravity well itself to build up speed— And you release a cable ahead of you, that swings down through the atmosphere to zero surface velocity at the point of your perigee, so your away team and their new friends can attach it to a glass elevator and be smoothly hoisted into space.
> If you have the power to cross the stars, surely taking off from a steep gravity well wouldn't be a problem.
Different problems entirely. You don't need a lot of thrust to get to high velocities. But you need a lot of thrust to leave a planets gravity well. On a planet, your thrust needs to win not only gravity, but also any atmospheric losses. E.g. on a 3g planet, you'd need thurst in excess of 3g's to leave.
But to reach say 0.25c, a tiny ion engine over a long enough time would suffice. an engine that wouldn't even get you off of earth.
Different problems entirely. You don't need a lot of thrust to get to high velocities. But you need a lot of thrust to leave a planets gravity well. On a planet, your thrust needs to win not only gravity, but also any atmospheric losses. E.g. on a 3g planet, you'd need thurst in excess of 3g's to leave.
But to reach say 0.25c, a tiny ion engine over a long enough time would suffice. an engine that wouldn't even get you off of earth.
> But to reach say 0.25c, a tiny ion engine over a long enough time would suffice.
Tsiolkovsky says otherwise, by a factor of over 10^663 (not even counting relativity):
https://www.wolframalpha.com/input?i=1%2Fe%5E%2874900km%2Fs%...
…Seriously. I tried to figure out just how much xenon you'd need to make that work. But you'd need to be able to store it in something like 15-dimensional space to even fit it within the diameter of the observable universe. And even if your ion engine and Hubble-scale fuel tank weighed less than the mass of the lightest quarks, the amount of propellant you'd need for it to reach 0.25c is still well over 10^600 times the combined mass of the entire observable universe, and would also collapse somewhere around 10^600 times the diameter of the observable universe into a single black hole:
https://www.wolframalpha.com/input?i=2G%282.2MeV%2Fc%C2%B2%2...
Of course, this also shows the intent of my original comment: Energy density matters, and somebody packing enough to casually cross interstellar densities isn't going to struggle with a planetary gravity well unless Idk they're doing like a low-tech off-grid trend or something.
Also, skyhooks!
Tsiolkovsky says otherwise, by a factor of over 10^663 (not even counting relativity):
https://www.wolframalpha.com/input?i=1%2Fe%5E%2874900km%2Fs%...
…Seriously. I tried to figure out just how much xenon you'd need to make that work. But you'd need to be able to store it in something like 15-dimensional space to even fit it within the diameter of the observable universe. And even if your ion engine and Hubble-scale fuel tank weighed less than the mass of the lightest quarks, the amount of propellant you'd need for it to reach 0.25c is still well over 10^600 times the combined mass of the entire observable universe, and would also collapse somewhere around 10^600 times the diameter of the observable universe into a single black hole:
https://www.wolframalpha.com/input?i=2G%282.2MeV%2Fc%C2%B2%2...
Of course, this also shows the intent of my original comment: Energy density matters, and somebody packing enough to casually cross interstellar densities isn't going to struggle with a planetary gravity well unless Idk they're doing like a low-tech off-grid trend or something.
Also, skyhooks!
Maybe light sail and beaming energy from the home planet?
More workable:
https://en.wikipedia.org/wiki/Breakthrough_Starshot
Power density still matters though. Diffraction would get in the way at long-duration low-thrust.
https://en.wikipedia.org/wiki/Breakthrough_Starshot
Power density still matters though. Diffraction would get in the way at long-duration low-thrust.
Well, you could send remotely controlled probes. And there might be some volunteers for a one-way trip, too. There are certainly volunteers for one-way trips to Mars right now, and by the time humanity would be an interstellar species, our population size would have gone up by several orders of magnitude; so even if volunteers are rarer as a proportion, they would be much more numerous in absolute terms.
Rockets are out, but you could drop a space-elevator line down
Higher gravity means space elevator might be infeasible as well. It's barely feasible on Earth.
No advanced civilization would conclude they are dealing with "gods" just because they see someone with presumably better technology than themselves.
In fact, if they are anything like humans, they have probably already realized that species that live on a lower-gravity planet could escape that planet using the same chemical reactions that are available to them also.
In fact, if they are anything like humans, they have probably already realized that species that live on a lower-gravity planet could escape that planet using the same chemical reactions that are available to them also.
Is this really a big factor?
Not being multiplanetary seems like the least of our existential problems here on Earth, and will continue to be that way for awhile.
At the same time, chemical rocket efficiency becomes totally irrelevant for a slightly more advanced civilization than us.
Not being multiplanetary seems like the least of our existential problems here on Earth, and will continue to be that way for awhile.
At the same time, chemical rocket efficiency becomes totally irrelevant for a slightly more advanced civilization than us.
You can't build a space elevator before getting to the orbit first.
A jet engine capable of leaving a deep gravitational well must have a big ratio of thrust to weight. If a chemical rocket is too weak, a nuclear jet engine is the only remaining option. Would you be comfortable running it in the thick atmosphere of a densely inhabited planet?
A jet engine capable of leaving a deep gravitational well must have a big ratio of thrust to weight. If a chemical rocket is too weak, a nuclear jet engine is the only remaining option. Would you be comfortable running it in the thick atmosphere of a densely inhabited planet?
A civilization just a few decades ahead of us is (theoretically) almost unimaginable. Bio augmentation, true AIs, who knows what advances in fundamental physics knowledge... Just to start.
What I'm saying is that whatever engineering and environmental limitations we currently perceive are probably irrelevant.
What I'm saying is that whatever engineering and environmental limitations we currently perceive are probably irrelevant.
> Not being multiplanetary seems like the least of our existential problems here on Earth, and will continue to be that way for awhile.
That might be true, especially if your 'for awhile' talks about millennia at most.
But it's an extremely relevant concern in the context of the Fermi paradox.
That might be true, especially if your 'for awhile' talks about millennia at most.
But it's an extremely relevant concern in the context of the Fermi paradox.
Yeah, but those evolved on high-gravity planets are smarter (and maybe stronger) since they too must calculate thrown-object trajectories but have to do so faster. Our brains use just enough energy, but no more, to keep us alive. Being smarter than we are would be a waste .... but if we HAD to think faster, we would evolve to match.
So maybe they'd figure it out.
So maybe they'd figure it out.
Humans are (nearly?) the only animals that got really into throwing stuff, especially throwing stuff with heft and precision. (As a corollary: you can train seals to balance balls, and apes might through excrement; but only (some) humans can juggle.)
If throwing things well had been much harder, perhaps no animal would have ever bothered?
If throwing things well had been much harder, perhaps no animal would have ever bothered?
The article limits itself to chemical rockets. They work well enough on Earth so that's what we are using, but we can do better. Replace chemistry with nuclear, and use the air in the atmosphere as a reaction mass. On Earth, that would cause more problems than it would solve, that's why we don't do that despite having the tech to do it. But on a higher gravity planet it may be what we would do. Harder, but not impossible.
It is interesting how we got nuclear technology that would allow for way more capable rockets at the same time we perfected chemical rockets enough to get to orbit. So much that we could have been able to escape a 10g planet almost as soon as we have escaped Earth.
It is interesting how we got nuclear technology that would allow for way more capable rockets at the same time we perfected chemical rockets enough to get to orbit. So much that we could have been able to escape a 10g planet almost as soon as we have escaped Earth.
If you want to use nuclear technology to get to orbit on a planet with an atmosphere, you pretty much have to use bombs. See https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...
More conventional nuclear propulsion has similar trade-offs to an ion drive: great for long distance travel when you are already in space, but useless to get off a planet.
More conventional nuclear propulsion has similar trade-offs to an ion drive: great for long distance travel when you are already in space, but useless to get off a planet.
> […] ability to become multiplanetary and survive great filters is limited.
So, the known quantities that term refers to tend to be steps more like planetary habitability and abiogenesis, which might prevent complex life from getting established in the first place. But it sounds like you mean some kind of cataclysmic event which wipes out an already existing industrialized civilization.
What, specifically, are the "Great Filter" scenarios which being multiplanetary is actually supposed to help with?
Supernovas? GRBs? Simple asteroid impacts? You can usually see those coming from millions of years in advance. And surely building a couple layers of solar sail material to shield the planet, stockpiling ozone generators to repair the damage quickly, gently nudging the asteroid, or simply digging some holes/eating a gas giant and weathering the storm, would be easier and save vastly more people than establishing a sizable population in another star system.
The other "Great Filter" idea which seems to be memetically adapted for proliferating in modern discourse is the idea of a locust-like swarm of technologically advanced aliens that kill any industrial civilizations which do emerge. But in that case, presumably settling multiple star systems is the opposite of what you'd want to do; You'd be better off quieting your emissions to shrink your footprint than spreading even more biomarkers around at high blueshift.
Frankly, I think this entire idea of needing to "become multiplanetary and survive great filters" is more mainstreamed now largely due to one specific individual fancying himself a savior of humanity. SpaceX builds interesting machines, but I liked it better when it was people like Sagan, Aldrin, and Zubrin getting excited about Mars.
But even then, I'm not sure if the idea of colonizing more planets in order to survive planet-scale catastrophes really jives with how people think— Plenty of us already live within splash radius of the Pacific Ring of Fire, Yellowstone Caldera, tornadoes, tropical cyclones, land below sea level… and yet there's no billion-dollar emergency backup cities in Antarctica to "make San Francisco into a multicontinental city and survive great quakings".
So, the known quantities that term refers to tend to be steps more like planetary habitability and abiogenesis, which might prevent complex life from getting established in the first place. But it sounds like you mean some kind of cataclysmic event which wipes out an already existing industrialized civilization.
What, specifically, are the "Great Filter" scenarios which being multiplanetary is actually supposed to help with?
Supernovas? GRBs? Simple asteroid impacts? You can usually see those coming from millions of years in advance. And surely building a couple layers of solar sail material to shield the planet, stockpiling ozone generators to repair the damage quickly, gently nudging the asteroid, or simply digging some holes/eating a gas giant and weathering the storm, would be easier and save vastly more people than establishing a sizable population in another star system.
The other "Great Filter" idea which seems to be memetically adapted for proliferating in modern discourse is the idea of a locust-like swarm of technologically advanced aliens that kill any industrial civilizations which do emerge. But in that case, presumably settling multiple star systems is the opposite of what you'd want to do; You'd be better off quieting your emissions to shrink your footprint than spreading even more biomarkers around at high blueshift.
Frankly, I think this entire idea of needing to "become multiplanetary and survive great filters" is more mainstreamed now largely due to one specific individual fancying himself a savior of humanity. SpaceX builds interesting machines, but I liked it better when it was people like Sagan, Aldrin, and Zubrin getting excited about Mars.
But even then, I'm not sure if the idea of colonizing more planets in order to survive planet-scale catastrophes really jives with how people think— Plenty of us already live within splash radius of the Pacific Ring of Fire, Yellowstone Caldera, tornadoes, tropical cyclones, land below sea level… and yet there's no billion-dollar emergency backup cities in Antarctica to "make San Francisco into a multicontinental city and survive great quakings".
> surely building a couple layers of solar sail material to shield the planet, stockpiling ozone generators to repair the damage quickly, gently nudging the asteroid, or simply digging some holes/eating a gas giant and weathering the storm, would be easier
The assumption is that we have a problem getting anything off the planet. All these would require some good rocket engineering.
I agree with everything else here a lot.
The assumption is that we have a problem getting anything off the planet. All these would require some good rocket engineering.
I agree with everything else here a lot.
Maybe if you can't launch rockets into orbit with chemical rockets then your path to becoming multiplanetary would probably be quicker rather than slower. You would have to develop nuclear rockets (quite doable) and then have a much better tech for exploring the solar system and beyond.
Is there an equivalent to the Drake equation that includes a factor that describes planets small enough to escape?
Very depressing to me to think about how vanishingly rare smart, spacefaring life might be. But on the flipside of that, there may be a little corner of the universe where multiple spacefarers contemporaneously live within a few light years of each other. That might be cool from a space opera point of view but it'd probably end up being dominated by a space fascist enslaving everyone.
Very depressing to me to think about how vanishingly rare smart, spacefaring life might be. But on the flipside of that, there may be a little corner of the universe where multiple spacefarers contemporaneously live within a few light years of each other. That might be cool from a space opera point of view but it'd probably end up being dominated by a space fascist enslaving everyone.
Rockets are not the only way off a planet. If humans had spent space program amounts of resources on railguns or another method of locomotion there's real possibility it would have been successful too.
Rockets are most convenient for Earth's variables so engineers optimized for them.
Rockets are most convenient for Earth's variables so engineers optimized for them.
Railguns also become much harder in a larger gravity well. Bigger planets generally have thicker atmospheres as well. Your payload will end up disintegrating at the velocities required even on Earth.
The Earth is larger than Venus, but its atmosphere is 90 times denser than ours.
There's a lot more variables that just gravity.
There's a lot more variables that just gravity.
Balloon stage followed by a rail gun might work.
Vacuum inside the tube?
> That might be cool from a space opera point of view but it'd probably end up being dominated by a space fascist enslaving everyone.
Fascism already barely works on earth, and gets out-competed. See https://tvtropes.org/pmwiki/pmwiki.php/Main/FascistButIneffi... Similarly with slavery. (See https://www.econlib.org/library/Columns/LevyPeartdismal.html to go off an slight tangent.)
In space, slavery is even less useful. That's mostly because humans are even less useful: we are already doing pretty much all of our useful space exploration with robots, and sending humans is just for bragging rights. Keeping space slaves alive costs you more than they ever could conceivably do for you.
Of course, aliens might have biologies that are much better adapted to surviving in space, maybe?
Fascism already barely works on earth, and gets out-competed. See https://tvtropes.org/pmwiki/pmwiki.php/Main/FascistButIneffi... Similarly with slavery. (See https://www.econlib.org/library/Columns/LevyPeartdismal.html to go off an slight tangent.)
In space, slavery is even less useful. That's mostly because humans are even less useful: we are already doing pretty much all of our useful space exploration with robots, and sending humans is just for bragging rights. Keeping space slaves alive costs you more than they ever could conceivably do for you.
Of course, aliens might have biologies that are much better adapted to surviving in space, maybe?
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I think mostly the Drake equation shows a lack of imagination about the forms life might take. Every time you add a term to it, you're baking in additional assumptions.
Maybe. But you still have to explain the observation that the night sky is empty of signs of life.
Keep in mind that human technology is pretty close to being good enough to detect not just foreign civilisations (via eg radio waves), but signs of life itself: studying the spectra of light reflected by exoplanets can tell you what chemical elements are in their atmosphere, so you can detect atmospheres that are far from chemical equilibrium, like earth's oxygen rich one.
We emitted radio waves for only a few decades. But earth had oxygen for billions of years. So that widens the window of time of development that we could detect.
Keep in mind that human technology is pretty close to being good enough to detect not just foreign civilisations (via eg radio waves), but signs of life itself: studying the spectra of light reflected by exoplanets can tell you what chemical elements are in their atmosphere, so you can detect atmospheres that are far from chemical equilibrium, like earth's oxygen rich one.
We emitted radio waves for only a few decades. But earth had oxygen for billions of years. So that widens the window of time of development that we could detect.
> But you still have to explain the observation that the night sky is empty of signs of life.
It's really not that hard to explain. The last time I looked into this it was the case that we wouldn't be able to detect ourselves more than a light year out. The closest star is the red dwarf flare star Proxima Centauri at 4.2 ly. So, the question really isn't "where is everyone?" but "why is no one doing active SETI right now in a way that we can detect?".
That's exactly OPs point, we are heaping assumptions upon assumptions and most people discussing this topic don't even know how mind bogglingly huge those assumptions really are.
It's really not that hard to explain. The last time I looked into this it was the case that we wouldn't be able to detect ourselves more than a light year out. The closest star is the red dwarf flare star Proxima Centauri at 4.2 ly. So, the question really isn't "where is everyone?" but "why is no one doing active SETI right now in a way that we can detect?".
That's exactly OPs point, we are heaping assumptions upon assumptions and most people discussing this topic don't even know how mind bogglingly huge those assumptions really are.
You are underestimating the Fermi Paradox. Active SETI is barely relevant.
The first part:
See how fast technology is developing, and especially the decreases in the cost of rocket launches.
Within the next few hundred years humanity (or our drones) will have spread to countless habitats around the solar system. Within a few thousand years, we will have started building a Dyson swarm that will obscure a measurable fraction of the light of our sun.
We don't need any new science for this, nor radically new engineering.
For this confident prediction, we only need a few key ingredients:
* Humanity doesn't blow herself up completely. (Civilisations blowing themselves up is one way to resolve the Fermi paradox.)
* At least some humans are interested in space exploration. (The proportion of the total population can even go down compared to today.)
A thousand years is nothing on cosmic time scales. It's not even much in terms of geological time scales.
Even today's technology could detect the humanity of 3024 from countless light years away: just point a spectroscope at the star and notice a vast excess of infrared (the waste heat of our solar collectors has to go somewhere) and an corresponding deficit of shorter wavelengths.
So we might not be able to detect ourselves at the moment, but we would be able to detect our 20-minutes-into-the-future selves already.
The second part:
As I already mentioned, our sensor are pretty close to good enough to measure the chemical make-up of the atmospheres of exoplanets via spectroscopy. Atmospheres that harbour life look very, very different from those of life-less planets.
(Or to steelman that argument against nitpicks: there might be some forms of life that do not push the atmosphere of their planet out of chemical equilibrium. But for that to resolve the Fermi Paradox, that would need to be the vast, vast majority of biospheres.
And I'm not talking about an oxygen-rich atmosphere necessarily. Just any sign of chemical disequilibrium.)
So, yes, humanity couldn't detect ourselves right now. But humanity in a only few years could already detect signs of life hundreds of light years away while still at the equivalent of the Cambrian explosion.
Strictly speaking my part two is not a problem right now in 2024, but I'm fairly confident in predicting it will become acute in the next ten years as our telescopes get better. Astronomers have already done some basic spectroscopy on some exoplanets. Their skills are only improving.
---
You are right to warn about making too many assumptions about alien life. However, not all assumptions are born equal.
For example, life is almost by definition associated with being far outside thermodynamic equilibrium. Being outside of chemical equilibrium isn't much of a stretch.
Similarly, my first part assumes that humanity (or our alien equivalents) will keep multiplying and expanding. And again, that's not much of a stretch: yes, at any given time only some portion of life might be interested in these activities, but future generations will be predominately made up of those that showed the greatest interested and skill in multiplying.
The first part:
See how fast technology is developing, and especially the decreases in the cost of rocket launches.
Within the next few hundred years humanity (or our drones) will have spread to countless habitats around the solar system. Within a few thousand years, we will have started building a Dyson swarm that will obscure a measurable fraction of the light of our sun.
We don't need any new science for this, nor radically new engineering.
For this confident prediction, we only need a few key ingredients:
* Humanity doesn't blow herself up completely. (Civilisations blowing themselves up is one way to resolve the Fermi paradox.)
* At least some humans are interested in space exploration. (The proportion of the total population can even go down compared to today.)
A thousand years is nothing on cosmic time scales. It's not even much in terms of geological time scales.
Even today's technology could detect the humanity of 3024 from countless light years away: just point a spectroscope at the star and notice a vast excess of infrared (the waste heat of our solar collectors has to go somewhere) and an corresponding deficit of shorter wavelengths.
So we might not be able to detect ourselves at the moment, but we would be able to detect our 20-minutes-into-the-future selves already.
The second part:
As I already mentioned, our sensor are pretty close to good enough to measure the chemical make-up of the atmospheres of exoplanets via spectroscopy. Atmospheres that harbour life look very, very different from those of life-less planets.
(Or to steelman that argument against nitpicks: there might be some forms of life that do not push the atmosphere of their planet out of chemical equilibrium. But for that to resolve the Fermi Paradox, that would need to be the vast, vast majority of biospheres.
And I'm not talking about an oxygen-rich atmosphere necessarily. Just any sign of chemical disequilibrium.)
So, yes, humanity couldn't detect ourselves right now. But humanity in a only few years could already detect signs of life hundreds of light years away while still at the equivalent of the Cambrian explosion.
Strictly speaking my part two is not a problem right now in 2024, but I'm fairly confident in predicting it will become acute in the next ten years as our telescopes get better. Astronomers have already done some basic spectroscopy on some exoplanets. Their skills are only improving.
---
You are right to warn about making too many assumptions about alien life. However, not all assumptions are born equal.
For example, life is almost by definition associated with being far outside thermodynamic equilibrium. Being outside of chemical equilibrium isn't much of a stretch.
Similarly, my first part assumes that humanity (or our alien equivalents) will keep multiplying and expanding. And again, that's not much of a stretch: yes, at any given time only some portion of life might be interested in these activities, but future generations will be predominately made up of those that showed the greatest interested and skill in multiplying.
> See how fast technology is developing, and especially the decreases in the cost of rocket launches.
The past century of rapid progress is anomalous in human history. We made do with stone tools for 100k years. In the middle ages basically nothing technological happened for a 1000 years. Consequently, this view of eternally ongoing progress is an artifact of the specific time and place we find ourselves in and not something that really has to happen. While we had some good results from semi-conductors I see our progress as already slowing down. Most of our science doesn't reproduce. Our cosmology is in shambles (more on this later) and our engineering is surfacing issues around putting the correct number of bolts on airplanes.
> Within the next few hundred years humanity (or our drones) will have spread to countless habitats around the solar system.
Why? What is there beyond the gravity well that isn't on earth? Maybe there are some substances, such as deuterium, that we can exploit remotely but this idea of "space habitats" is just romantic science fiction. Maybe someone will make it happen but only because we humans are in love with space, not because it makes rational sense.
> Within a few thousand years, we will have started building a Dyson swarm that will obscure a measurable fraction of the light of our sun.
Again, why? Fusion and fission can supply all the energy we want. If we want to do mega engineering for more energy we could just bore down to the earth's core. I'd bet that's what intelligent aliens on Enceladus would do. Regardless, it's completely useless to predict the future a thousand years out. We simply don't know and we have no data to anchor our fantasies to reality. From this initial starting point, nobody ever made and predictions worth anything.
> We don't need any new science for this, nor radically new engineering.
So why don't we do it then?
> For this confident prediction, we only need a few key ingredients: > > * Humanity doesn't blow herself up completely. (Civilisations blowing > themselves up is one way to resolve the Fermi paradox.)
Like I showed, you are baking in more and more assumption. Basically every sentence of yours is one more huge assumption.
> Even today's technology could detect the humanity of 3024 from countless light years away: just point a spectroscope at the star and notice a vast excess of infrared (the waste heat of our solar collectors has to go somewhere) and an corresponding deficit of shorter wavelengths.
Some SETI and Fermilab people looked already back in 2006 and found 17 candidates. There is this flawed idea that we already have detected and interpreted everything that there is. But JWST is showing us right now that we don't know anything. Every piece of our cosmology is currently under reexamination because wherever we point JWST we see stuff we can't explain. Even just the question of cosmic distance measurement isn't simple and clean cut.
All our space science is based on the premise that we are doing natural science where natural things exhibit regular patterns that we can describe with laws. If the universe were to contain ubiquitous mega engineering we would, by definition of the science we are doing, not recognize it. For instance, your Dyson spheres detection assumes that we see an abnormal spectrum. But, abnormal compared to what? If the universe was full of Dyson spheres we would say that there are "infrared stars" and then we would hypothesize how these come about naturally until someone can crowbar in an explanation that sort-of-kinda could work. Cosmology is full of these kinds of after-the-fact explanations btw, just look at Tabby's star or Oumuamua.
So again, we end up at a place where the Fermi paradox isn't very impressive. If the aren't building (arguably pointless) mega structures, we won't see them. If they all are doing mega engineering we wouldn't recognize it. For us to see them the aliens must be doing things that are very 20th century western hemisphere human things.
The past century of rapid progress is anomalous in human history. We made do with stone tools for 100k years. In the middle ages basically nothing technological happened for a 1000 years. Consequently, this view of eternally ongoing progress is an artifact of the specific time and place we find ourselves in and not something that really has to happen. While we had some good results from semi-conductors I see our progress as already slowing down. Most of our science doesn't reproduce. Our cosmology is in shambles (more on this later) and our engineering is surfacing issues around putting the correct number of bolts on airplanes.
> Within the next few hundred years humanity (or our drones) will have spread to countless habitats around the solar system.
Why? What is there beyond the gravity well that isn't on earth? Maybe there are some substances, such as deuterium, that we can exploit remotely but this idea of "space habitats" is just romantic science fiction. Maybe someone will make it happen but only because we humans are in love with space, not because it makes rational sense.
> Within a few thousand years, we will have started building a Dyson swarm that will obscure a measurable fraction of the light of our sun.
Again, why? Fusion and fission can supply all the energy we want. If we want to do mega engineering for more energy we could just bore down to the earth's core. I'd bet that's what intelligent aliens on Enceladus would do. Regardless, it's completely useless to predict the future a thousand years out. We simply don't know and we have no data to anchor our fantasies to reality. From this initial starting point, nobody ever made and predictions worth anything.
> We don't need any new science for this, nor radically new engineering.
So why don't we do it then?
> For this confident prediction, we only need a few key ingredients: > > * Humanity doesn't blow herself up completely. (Civilisations blowing > themselves up is one way to resolve the Fermi paradox.)
Like I showed, you are baking in more and more assumption. Basically every sentence of yours is one more huge assumption.
> Even today's technology could detect the humanity of 3024 from countless light years away: just point a spectroscope at the star and notice a vast excess of infrared (the waste heat of our solar collectors has to go somewhere) and an corresponding deficit of shorter wavelengths.
Some SETI and Fermilab people looked already back in 2006 and found 17 candidates. There is this flawed idea that we already have detected and interpreted everything that there is. But JWST is showing us right now that we don't know anything. Every piece of our cosmology is currently under reexamination because wherever we point JWST we see stuff we can't explain. Even just the question of cosmic distance measurement isn't simple and clean cut.
All our space science is based on the premise that we are doing natural science where natural things exhibit regular patterns that we can describe with laws. If the universe were to contain ubiquitous mega engineering we would, by definition of the science we are doing, not recognize it. For instance, your Dyson spheres detection assumes that we see an abnormal spectrum. But, abnormal compared to what? If the universe was full of Dyson spheres we would say that there are "infrared stars" and then we would hypothesize how these come about naturally until someone can crowbar in an explanation that sort-of-kinda could work. Cosmology is full of these kinds of after-the-fact explanations btw, just look at Tabby's star or Oumuamua.
So again, we end up at a place where the Fermi paradox isn't very impressive. If the aren't building (arguably pointless) mega structures, we won't see them. If they all are doing mega engineering we wouldn't recognize it. For us to see them the aliens must be doing things that are very 20th century western hemisphere human things.
You are right that the time since the industrial revolution (or perhaps since the start of the scientific revolution) was especially fast and things might not continue at this blistering pace. However we are already on edge of being able to settle the solar system; or to transform it with unmanned probes. Not much more progress is necessary. (Especially no new science. Engineering advances are welcome, of course.)
> Why? What is there beyond the gravity well that isn't on earth? Maybe there are some substances, such as deuterium, that we can exploit remotely but this idea of "space habitats" is just romantic science fiction. Maybe someone will make it happen but only because we humans are in love with space, not because it makes rational sense.
My argument does not require space exploration (or even life in general) to make any 'rational sense'. It just requires that some fraction of people are interested in it.
> There is this flawed idea that we already have detected and interpreted everything that there is.
Huh? Who has that idea?
> If the aren't building (arguably pointless) mega structures, we won't see them.
The Fermi Paradox does not require that mega structures have a point that you can understand. You talk a big game about being careful about our assumptions, but you can't even understand that some of your fellow humans might do 'pointless' things?
> If they all are doing mega engineering we wouldn't recognize it.
I don't buy your argument. Aliens can't magically escape thermodynamics, even if they were super quirky and 'alien'.
We don't see these 'infrared stars'.
> Why? What is there beyond the gravity well that isn't on earth? Maybe there are some substances, such as deuterium, that we can exploit remotely but this idea of "space habitats" is just romantic science fiction. Maybe someone will make it happen but only because we humans are in love with space, not because it makes rational sense.
My argument does not require space exploration (or even life in general) to make any 'rational sense'. It just requires that some fraction of people are interested in it.
> There is this flawed idea that we already have detected and interpreted everything that there is.
Huh? Who has that idea?
> If the aren't building (arguably pointless) mega structures, we won't see them.
The Fermi Paradox does not require that mega structures have a point that you can understand. You talk a big game about being careful about our assumptions, but you can't even understand that some of your fellow humans might do 'pointless' things?
> If they all are doing mega engineering we wouldn't recognize it.
I don't buy your argument. Aliens can't magically escape thermodynamics, even if they were super quirky and 'alien'.
We don't see these 'infrared stars'.
So the starting point of this conversation is the Fermi paradox. Your line of reasoning has a very long line of necessary assumption. I only show that how they might not be warranted.
> Not much more progress is necessary.
The more plausible you make the technology the more you have to explain why we aren't doing these things. We might go back to the moon soon but beyond that we don't have any plausible plans to do anything noteworthy in space, let alone activities that would be detectable from other star systems.
> Huh? Who has that idea?
You. Everyone else who holds up the Fermi Paradox. The further we look into space, the less we understand but somehow you guys are so very sure that we aren't seeing aliens.
> It just requires that some fraction of people are interested in it.
I don't know how this relates to the Fermi paradox. Is the argument that "as long as some people are interested there will be a Dyson swarm"?. I don't think that follows.
> but you can't even understand that some of your fellow humans might do 'pointless' things?
I can absolutely understand that. What I don't agree with is that we are on an inevitable path to a Dyson swarm (or similar scale engineering).
> I don't buy your argument. Aliens can't magically escape thermodynamics, even if they were super quirky and 'alien'.
That wasn't my argument but I don't know what aliens can do. They might be able to do things that look a lot like violating thermodynamics to our incomplete understandings of physics. They might be engineering on a scale that is so fundamental that we can't currently recognize it. They might just be on their planet(s) with eternally stagnant technology. The point is, we don't know. We don't have data. We won't be able to draw valid conclusion from almost total ignorance.
> We don't see these 'infrared stars'.
It was a hypothetical. But let's say we don't see dyson swarms, which I am not even sure of, then proper conclusion is that nobody builds dyson swarms and nothing else.
> Not much more progress is necessary.
The more plausible you make the technology the more you have to explain why we aren't doing these things. We might go back to the moon soon but beyond that we don't have any plausible plans to do anything noteworthy in space, let alone activities that would be detectable from other star systems.
> Huh? Who has that idea?
You. Everyone else who holds up the Fermi Paradox. The further we look into space, the less we understand but somehow you guys are so very sure that we aren't seeing aliens.
> It just requires that some fraction of people are interested in it.
I don't know how this relates to the Fermi paradox. Is the argument that "as long as some people are interested there will be a Dyson swarm"?. I don't think that follows.
> but you can't even understand that some of your fellow humans might do 'pointless' things?
I can absolutely understand that. What I don't agree with is that we are on an inevitable path to a Dyson swarm (or similar scale engineering).
> I don't buy your argument. Aliens can't magically escape thermodynamics, even if they were super quirky and 'alien'.
That wasn't my argument but I don't know what aliens can do. They might be able to do things that look a lot like violating thermodynamics to our incomplete understandings of physics. They might be engineering on a scale that is so fundamental that we can't currently recognize it. They might just be on their planet(s) with eternally stagnant technology. The point is, we don't know. We don't have data. We won't be able to draw valid conclusion from almost total ignorance.
> We don't see these 'infrared stars'.
It was a hypothetical. But let's say we don't see dyson swarms, which I am not even sure of, then proper conclusion is that nobody builds dyson swarms and nothing else.
Thanks for the enlightening discussion!
> The more plausible you make the technology the more you have to explain why we aren't doing these things. We might go back to the moon soon but beyond that we don't have any plausible plans to do anything noteworthy in space, let alone activities that would be detectable from other star systems.
We are doing these things! It's just taking longer than people had expected in the 1960s. But in the timescales we are talking about for the Fermi paradox, an extra 100 years don't make a difference.
Arguably, going to the moon was a big waste of money for some bragging rights. More recently, rocket launch costs have decreased dramatically, and lots of space projects are only now becoming economically feasible. At the moment that's mostly a greatly increased rate of satellite launches, but we can already see asteroid mining on the horizon.
Collecting energy in space and beaming it to earth might also soon become economically feasible. Or perhaps the opposite: putting up a big sunshade at a Lagrange point to counteract global warming.
> I don't know how this relates to the Fermi paradox. Is the argument that "as long as some people are interested there will be a Dyson swarm"?. I don't think that follows.
Yes, you understood that right. As humanity becomes richer and more capable and space flight become easier, we'd need to commit proportionally less and less of our total resources to make a difference.
Compare eg how building something like GPT-4 would have been impossible in the 1990s; would have been Apollo program level expensive in the 2000s; is a major corporate investment at the moment; and will probably be something within the reach of hobbyists in the 2030s.
> I can absolutely understand that. What I don't agree with is that we are on an inevitable path to a Dyson swarm (or similar scale engineering).
I guess that's the crux of our disagreement. I predict the only way to avoid a Dyson swarm would be for humanity to blow itself up completely. (And even an AI singularity that sacrifices everything to the great paperclip maximiser would not avoid a Dyson swarm; just the opposite.)
> They might just be on their planet(s) with eternally stagnant technology.
Some aliens might do that. But to resolve the Fermi paradox, almost all alien civilisations would need to do that. If even one in a thousand have technological paths that are only even a 1% as fast as ours on earth, you'll get Dyson swarms.
It's theoretically possible that aliens might be able to do something that looks like violations of thermodynamics. Just like there's some possibility they might be able to go faster than light. But I'm excluding those possibilities here. (Or for the Fermi paradox to be still acute, it's enough if there's even a small fraction of Aliens who are bound by the same thermodynamics and lightspeed limits as we are.)
> It was a hypothetical. But let's say we don't see dyson swarms, which I am not even sure of, then proper conclusion is that nobody builds dyson swarms and nothing else.
Yes, as far as we can tell, nobody has build dyson swarms. But looking at our own technology, it looks like building dyson swarms should be fairly inevitable, once you have a tool using civilisation. So the conclusion is that it looks like there just aren't any civilisations even remotely comparable to earth.
---
To operationalise into something concrete that we could theoretically bet on:
I think a dyson swarm is at least a hundred years out, so that's too far out to bet. But as a precursor, I predict that launch costs per kg to an orbit of your choice will keep coming down; and that the number of launches will keep going up.
See the graph on https://en.wikipedia.org/wiki/Timeline_of_spaceflight#Orbita...
At the moment, we might be in a phase of exponential growth. I'm not sure that will keep on. But I predict at least a sustained linear growth in the total mass to orbit per year over the next few decades.
> The more plausible you make the technology the more you have to explain why we aren't doing these things. We might go back to the moon soon but beyond that we don't have any plausible plans to do anything noteworthy in space, let alone activities that would be detectable from other star systems.
We are doing these things! It's just taking longer than people had expected in the 1960s. But in the timescales we are talking about for the Fermi paradox, an extra 100 years don't make a difference.
Arguably, going to the moon was a big waste of money for some bragging rights. More recently, rocket launch costs have decreased dramatically, and lots of space projects are only now becoming economically feasible. At the moment that's mostly a greatly increased rate of satellite launches, but we can already see asteroid mining on the horizon.
Collecting energy in space and beaming it to earth might also soon become economically feasible. Or perhaps the opposite: putting up a big sunshade at a Lagrange point to counteract global warming.
> I don't know how this relates to the Fermi paradox. Is the argument that "as long as some people are interested there will be a Dyson swarm"?. I don't think that follows.
Yes, you understood that right. As humanity becomes richer and more capable and space flight become easier, we'd need to commit proportionally less and less of our total resources to make a difference.
Compare eg how building something like GPT-4 would have been impossible in the 1990s; would have been Apollo program level expensive in the 2000s; is a major corporate investment at the moment; and will probably be something within the reach of hobbyists in the 2030s.
> I can absolutely understand that. What I don't agree with is that we are on an inevitable path to a Dyson swarm (or similar scale engineering).
I guess that's the crux of our disagreement. I predict the only way to avoid a Dyson swarm would be for humanity to blow itself up completely. (And even an AI singularity that sacrifices everything to the great paperclip maximiser would not avoid a Dyson swarm; just the opposite.)
> They might just be on their planet(s) with eternally stagnant technology.
Some aliens might do that. But to resolve the Fermi paradox, almost all alien civilisations would need to do that. If even one in a thousand have technological paths that are only even a 1% as fast as ours on earth, you'll get Dyson swarms.
It's theoretically possible that aliens might be able to do something that looks like violations of thermodynamics. Just like there's some possibility they might be able to go faster than light. But I'm excluding those possibilities here. (Or for the Fermi paradox to be still acute, it's enough if there's even a small fraction of Aliens who are bound by the same thermodynamics and lightspeed limits as we are.)
> It was a hypothetical. But let's say we don't see dyson swarms, which I am not even sure of, then proper conclusion is that nobody builds dyson swarms and nothing else.
Yes, as far as we can tell, nobody has build dyson swarms. But looking at our own technology, it looks like building dyson swarms should be fairly inevitable, once you have a tool using civilisation. So the conclusion is that it looks like there just aren't any civilisations even remotely comparable to earth.
---
To operationalise into something concrete that we could theoretically bet on:
I think a dyson swarm is at least a hundred years out, so that's too far out to bet. But as a precursor, I predict that launch costs per kg to an orbit of your choice will keep coming down; and that the number of launches will keep going up.
See the graph on https://en.wikipedia.org/wiki/Timeline_of_spaceflight#Orbita...
At the moment, we might be in a phase of exponential growth. I'm not sure that will keep on. But I predict at least a sustained linear growth in the total mass to orbit per year over the next few decades.
Both lack of imagination of what life can be, and supporting factors we take for granted. I dismiss drake equation as fully useless as it doesn't provide useful upper nor lower bound.
Few lightyears is something like a hundred stars. Probably zero chance to nurture more than one unprobable life.
The upper limit on the size of the universe is infinite. So we can’t exactly rules stuff out for simply being improbable.
You can make a fairly strong statistical argument there are no spacefaring species in our galaxy. Even at 1% the speed of light a species could fully colonize the galaxy in 10 million years, 0.1% the age of the universe.
That we see nothing implies intellgent life is rare, short lived, or we're early in the age of the universe. For example, red dwarfs will last trillions of years compared to the sun's 5B lifespan.
That we see nothing implies intellgent life is rare, short lived, or we're early in the age of the universe. For example, red dwarfs will last trillions of years compared to the sun's 5B lifespan.
> That we see nothing implies intellgent life is rare, short lived, or we're early in the age of the universe.
Or it implies that not everybody's first instinct on seeing a vast galaxy is to try to take it over ASAP.
If you want resources for quality of life— Gas giants are a thing. If you're an explorer driven by curiosity, then take only samples, leave only memories, right.
If you want money— Century-long shipping times with civilization-scaled fuel costs tend to eat into profit margins.
If you're worried about survival— genuinely worried about survival, on a level personal enough to motivate action, not just academically or for fun— then the focus is on people you know and care about; all of those are here.
In fact, I suspect the ones that see other stars and immediately think "Mine mine all mine!" probably have a higher chance of nuking themselves before they even get out of their star system.
Or it implies that not everybody's first instinct on seeing a vast galaxy is to try to take it over ASAP.
If you want resources for quality of life— Gas giants are a thing. If you're an explorer driven by curiosity, then take only samples, leave only memories, right.
If you want money— Century-long shipping times with civilization-scaled fuel costs tend to eat into profit margins.
If you're worried about survival— genuinely worried about survival, on a level personal enough to motivate action, not just academically or for fun— then the focus is on people you know and care about; all of those are here.
In fact, I suspect the ones that see other stars and immediately think "Mine mine all mine!" probably have a higher chance of nuking themselves before they even get out of their star system.
> That we see nothing implies intellgent life is rare, short lived, or we're early in the age of the universe.
> > Or it implies that not everybody's first instinct on seeing a vast galaxy is to try to take it over ASAP.
Or it may simply imply that intelligent life is good at hiding and does not want to be seen e.g. the dark forest hypothesis.
> > Or it implies that not everybody's first instinct on seeing a vast galaxy is to try to take it over ASAP.
Or it may simply imply that intelligent life is good at hiding and does not want to be seen e.g. the dark forest hypothesis.
Dark forest hypothesis uses lack of evidence as evidence. There is little to back the claim the galaxy is full, BUT if it is full then the Dark Forest could be a reason we haven't detected.
1% the speed of light is stupidly fast to colonize a galaxy. It only sounds reasonable in the same way startup claim if we can just capture 1% of the X market, while forgetting numbers much smaller exist.
Let’s assume super tech they can build that somehow allows vastly faster speeds than we can today ~120 km/s worth of DeltaV. Half that is spent slowing down so we’re talking 0.02% c.
Now let’s assume half the time is spent in flight and half the time is spent colonizing stars before launching ships. So now we’re down to 0.01% C. Suddenly 1 Billion years is a more reasonable estimate and even that takes super tech we don’t have any idea how to build and assumes nothing fails.
Several more advanced civilizations could be colonizing the galaxy today that are still 10 billion years from finishing.
Let’s assume super tech they can build that somehow allows vastly faster speeds than we can today ~120 km/s worth of DeltaV. Half that is spent slowing down so we’re talking 0.02% c.
Now let’s assume half the time is spent in flight and half the time is spent colonizing stars before launching ships. So now we’re down to 0.01% C. Suddenly 1 Billion years is a more reasonable estimate and even that takes super tech we don’t have any idea how to build and assumes nothing fails.
Several more advanced civilizations could be colonizing the galaxy today that are still 10 billion years from finishing.
Fusion rockets would be able to get over 1% c. I think the theoretical maximum for fusion is around 10%.
Fusion rockets might be able to get a sufficiently large spacecraft over 1% c. If you’re instead sending multiple generations of craft and waiting until each succeeds then it’s 1/n %c etc.
Colonization using a massive habitat capable of extreme redundancy and asteroid mining could be a completely viable solution to colonization. But such a structure wouldn’t be light.
Hitting 1% c could very well take megastructures that a civilization would rather spend on redundant craft etc. We can dream, but we’re nowhere close to being able to say what’s actually viable.
Colonization using a massive habitat capable of extreme redundancy and asteroid mining could be a completely viable solution to colonization. But such a structure wouldn’t be light.
Hitting 1% c could very well take megastructures that a civilization would rather spend on redundant craft etc. We can dream, but we’re nowhere close to being able to say what’s actually viable.
If the universe is Einsteinian, I don't think "colonizing" the stars is a thing that makes sense. We might do it once because we are sentimental like that but maybe that's owed to unique psychology owed to unique circumstances on earth.
I don't see how you could rationally justify spending this stupefying amount of resources on sending people into the void where, even if all goes well, you can barely talk to them, have no trade and no social contact with them at all.`
Basically you are paying to split off a one-way branch of the species. Just consider that if we could colonize Alpha Centauri that means that each message has a 8 year or 1/10 of a human life span roundtrip. What would you even talk about with that kind of latency?
I don't see how you could rationally justify spending this stupefying amount of resources on sending people into the void where, even if all goes well, you can barely talk to them, have no trade and no social contact with them at all.`
Basically you are paying to split off a one-way branch of the species. Just consider that if we could colonize Alpha Centauri that means that each message has a 8 year or 1/10 of a human life span roundtrip. What would you even talk about with that kind of latency?
Very shortminded and proto-humancentric thinking.
This is all done via AI and automated factories that terraform planets into Von Neumann manufacturing hubs, which then each send millions/billions of Von Neumann's out into the galaxy, each Von Neumann probe containing the tech/machinery to terraform another planet into another Dyson Sphere manufacturing hub. If you're really sentimental about humanity, you can include human DNA on the von neumann probess, and while the von neumann probe is terraforming a new planet, it can also grow humans in vitro.
Why would we (or our AI overlords) want to spread through the galaxy like this? Why does cancer spread through it's host? Why did europeans colonize the entire earth? Life is a virus that spreads without limit.
"I don't see how you could rationally justify spending this stupefying amount of resources on sending people into the void where, even if all goes well, you can barely talk to them, have no trade and no social contact with them at all."
Do you not understand why people invested in early merchant ships in like the 1500s? You spend a lot on a ship, send the ship to trade, and they come back with spice, that you sell at a profit, buy more ships, rinse and repeat. Same here: spend a couple quadrillion dollars, send off some von neumann probes, wait 50 million years, and then see if you've colonized a small cluster of the galaxy, or if your von neumann probe fleet was destroyed by a gamma ray burst or an uncharted supermassive black hole.
This is all done via AI and automated factories that terraform planets into Von Neumann manufacturing hubs, which then each send millions/billions of Von Neumann's out into the galaxy, each Von Neumann probe containing the tech/machinery to terraform another planet into another Dyson Sphere manufacturing hub. If you're really sentimental about humanity, you can include human DNA on the von neumann probess, and while the von neumann probe is terraforming a new planet, it can also grow humans in vitro.
Why would we (or our AI overlords) want to spread through the galaxy like this? Why does cancer spread through it's host? Why did europeans colonize the entire earth? Life is a virus that spreads without limit.
"I don't see how you could rationally justify spending this stupefying amount of resources on sending people into the void where, even if all goes well, you can barely talk to them, have no trade and no social contact with them at all."
Do you not understand why people invested in early merchant ships in like the 1500s? You spend a lot on a ship, send the ship to trade, and they come back with spice, that you sell at a profit, buy more ships, rinse and repeat. Same here: spend a couple quadrillion dollars, send off some von neumann probes, wait 50 million years, and then see if you've colonized a small cluster of the galaxy, or if your von neumann probe fleet was destroyed by a gamma ray burst or an uncharted supermassive black hole.
An immortal might justify sending automated probes to the nearest few systems to eventually collect resources and send them back to you.
But collecting resources from 10,000+ light years away just doesn’t make sense. By that point you have long since turned the local star system into a black hole via excess mass.
But collecting resources from 10,000+ light years away just doesn’t make sense. By that point you have long since turned the local star system into a black hole via excess mass.
> proto-humancentric thinking
I think that it's actually your perspective, which I think is essentially a sci-fi perspective, is deeply human biased. You think space is cool because you evolved under an open sky that rotates to show you "the universe" roughly every 12 hours. But most stars are red dwarfs and any planet with water they have would be tidally locked. I have my doubts that sky watching is a thing on such a planet given that the flares probably mean you have to live underground. Other places never show you the sky at all. For example, any species evolved in the oceans of Enceladus would have to through hundreds of kilometers of ice before understanding that there even IS a universe. Similarly for species evolved on clouded worlds like Venus or Titan. Their mythology and psychology would not resonate with space at all. Earths moon is also quite ridiculous. We don't see anything like it anywhere else. Now, would we all be so fascinated with space if we didn't have that moon and the eclipses to go along with it? I don't think so.
> This is all done via AI and automated factories that terraform planets into Von Neumann manufacturing hubs
But it is, very obviously, not done. And this is why I call yours a "sci fi perspective" because you hand wave away huge scientific and engineering challenges that might never be overcome. We have five (5!) probes that sort of accidentally left the solar system. We have 0 probes that we deliberately sent to other stars. We have 0 AI systems that can run factories. We have 0 autonomous factories. We have never made anything that ever extracted in-situ resources to be used by itself. We have 0 self-replicating machines. We have 0 self-repairing machines. We have grown human in-vitro 0 times. We have very little technology that can even survive a hundred years.
You have to understand that when Von Neuman talks about these probes it is little more than a doodle that illustrates a neat idea. There is nothing about reality that dictates that machines like this must be possible.
> Why did Europeans colonize the entire earth?
They did? Maybe you from an alternative earth but on my earth we (humans) haven't even colonized the poles, most deserts or oceans, all of which are magnitudes more habitable then anything we see in the night sky.
> Life is a virus that spreads without limit.
Von Neumann probes are lines of pencil on paper and nerve signal in brains and nothing more. But even if they existed they wouldn't be life.
> Do you not understand why people invested in early merchant ships in like the 1500s?
Yes, YOU invest, YOU get the spices. When you send for other stars you won't get anything back in your or your children's or your grandchildren's lifetime.
I think that it's actually your perspective, which I think is essentially a sci-fi perspective, is deeply human biased. You think space is cool because you evolved under an open sky that rotates to show you "the universe" roughly every 12 hours. But most stars are red dwarfs and any planet with water they have would be tidally locked. I have my doubts that sky watching is a thing on such a planet given that the flares probably mean you have to live underground. Other places never show you the sky at all. For example, any species evolved in the oceans of Enceladus would have to through hundreds of kilometers of ice before understanding that there even IS a universe. Similarly for species evolved on clouded worlds like Venus or Titan. Their mythology and psychology would not resonate with space at all. Earths moon is also quite ridiculous. We don't see anything like it anywhere else. Now, would we all be so fascinated with space if we didn't have that moon and the eclipses to go along with it? I don't think so.
> This is all done via AI and automated factories that terraform planets into Von Neumann manufacturing hubs
But it is, very obviously, not done. And this is why I call yours a "sci fi perspective" because you hand wave away huge scientific and engineering challenges that might never be overcome. We have five (5!) probes that sort of accidentally left the solar system. We have 0 probes that we deliberately sent to other stars. We have 0 AI systems that can run factories. We have 0 autonomous factories. We have never made anything that ever extracted in-situ resources to be used by itself. We have 0 self-replicating machines. We have 0 self-repairing machines. We have grown human in-vitro 0 times. We have very little technology that can even survive a hundred years.
You have to understand that when Von Neuman talks about these probes it is little more than a doodle that illustrates a neat idea. There is nothing about reality that dictates that machines like this must be possible.
> Why did Europeans colonize the entire earth?
They did? Maybe you from an alternative earth but on my earth we (humans) haven't even colonized the poles, most deserts or oceans, all of which are magnitudes more habitable then anything we see in the night sky.
> Life is a virus that spreads without limit.
Von Neumann probes are lines of pencil on paper and nerve signal in brains and nothing more. But even if they existed they wouldn't be life.
> Do you not understand why people invested in early merchant ships in like the 1500s?
Yes, YOU invest, YOU get the spices. When you send for other stars you won't get anything back in your or your children's or your grandchildren's lifetime.
That's why we typically only talk about the observable universe, which is very much finite.
>fascist
This word is wild. Very interesting.
It basically means "evil bad guy".
This word is wild. Very interesting.
It basically means "evil bad guy".
For the record (and the GP is using the term somewhat out of bounds), there are definitions of fascism that are rather tighter than 'evil bad guy': https://en.wikipedia.org/wiki/Ur-Fascism
That's a stronger definition, but it's still weak because it isn't primary source material. This guy isn't a disinterested political historian. Imagine taking as definition the views of Giovanni Gentile on Marxism.
I wouldn't call any of these groups "fascist" except in the loose pejorative sense
The closest governments to actual Fascism that I can think of are governments like modern China or even Singapore, and I don't mean that in a pejorative sense. They're just very fascist in character, i.e. national interest, social welfare, strong-arming of capital, etc.
I wouldn't call any of these groups "fascist" except in the loose pejorative sense
The closest governments to actual Fascism that I can think of are governments like modern China or even Singapore, and I don't mean that in a pejorative sense. They're just very fascist in character, i.e. national interest, social welfare, strong-arming of capital, etc.
If I had to describe fascism in one sentence it would rather be "take social darwinism 'the strong rule the weak' and add a pragmatic leader who helps your group crush those who hold you back and rule everyone else"
You know, exactly the kind of ideology you don't want a neighboring nation to have, no matter how you judge their actions morally
You know, exactly the kind of ideology you don't want a neighboring nation to have, no matter how you judge their actions morally
That's definitely not even close to reality.
National Socialism and Italian Fascism were all about the strong taking responsibility for the nation, in a philosophical sense.
These were social welfare states that provided for the "people" far more than modern American liberalism (the standard operating produre for free economies of scale in the modern world), for example.
Now, obviously I'm not saying this was a good system, but you're so far off base that it's ridiculous.
The discourse around this complex historical movement is profoundly anti-intellectual. I know this because I grew up in the same society you did, the one where I also learned and used fascist as a pejorative without any further information.
Now, as someone interested in having sophisticated ideas about systems, I'm not really in a mental state where I'm going to take appeals or emotion or shortcuts that shut down thought seriously. Regardless of the context, I still want to try and reflect reality as closely as possible in my minds eye.
How many liberal, or even communist thinkers have you read? Personally, countless. As for fascists, almost none. It's a taboo, the works aren't translated, etc -- but it's there, and has intellectual underpinning that is more complex than mindlessly calling people you don't like "fascists".
This can't be conscionable to any earnest intellectual. Imagine sitting here and tolerating people pejoratively calling people "communists". It's so stupid.
Edit: I get in trouble here because there's something really interesting going on with controversial topics: all you need to do is make a choice and your model of reality is much more accurate than the presented model of reality. It's the easiest way to take Ws out of discourse, nobody has good ideas when the id has the reins.
National Socialism and Italian Fascism were all about the strong taking responsibility for the nation, in a philosophical sense.
These were social welfare states that provided for the "people" far more than modern American liberalism (the standard operating produre for free economies of scale in the modern world), for example.
Now, obviously I'm not saying this was a good system, but you're so far off base that it's ridiculous.
The discourse around this complex historical movement is profoundly anti-intellectual. I know this because I grew up in the same society you did, the one where I also learned and used fascist as a pejorative without any further information.
Now, as someone interested in having sophisticated ideas about systems, I'm not really in a mental state where I'm going to take appeals or emotion or shortcuts that shut down thought seriously. Regardless of the context, I still want to try and reflect reality as closely as possible in my minds eye.
How many liberal, or even communist thinkers have you read? Personally, countless. As for fascists, almost none. It's a taboo, the works aren't translated, etc -- but it's there, and has intellectual underpinning that is more complex than mindlessly calling people you don't like "fascists".
This can't be conscionable to any earnest intellectual. Imagine sitting here and tolerating people pejoratively calling people "communists". It's so stupid.
Edit: I get in trouble here because there's something really interesting going on with controversial topics: all you need to do is make a choice and your model of reality is much more accurate than the presented model of reality. It's the easiest way to take Ws out of discourse, nobody has good ideas when the id has the reins.
> Imagine sitting here and tolerating people pejoratively calling people "communists".
Also tolerated - by calling them "Russians".
The logic goes, if there's nothing innately wrong with Communism then Russians (and, to extent, Chinese) must be up to blame.
Also tolerated - by calling them "Russians".
The logic goes, if there's nothing innately wrong with Communism then Russians (and, to extent, Chinese) must be up to blame.
That's pretty much it - if you check your history it's clear that neither Russia nor China adopted Communism in practice - they both went for authoritarian committe rule with power struggles as some kind of "neccessary" middle state while they work their way towards Twue Communism.
It was still way more socialist than what California or South European left wants.
Soviet Union had socialized assigned housing, affirmative action policy and equalized wages right from the start. Still, it is largely ignored by socialist LARPers of today.
Soviet Union had socialized assigned housing, affirmative action policy and equalized wages right from the start. Still, it is largely ignored by socialist LARPers of today.
Australia was and likely still is more socialist than any US centralists wants.
The 1900's Harvester agreement indexed the minimum wage to am eight hour work day with a week sufficient to feed, house, and clothe a worker and their family.
The Whitlam years saw free university education for anyone that merited by high school (and equivilency) exams, health care has been universal - now with a split of both public and private, pharmacy companies are capped on their generics so that costs are reasonable, differences are picked up for those that can't afford medication (for almost all prescriptions), etc.
The 1900's Harvester agreement indexed the minimum wage to am eight hour work day with a week sufficient to feed, house, and clothe a worker and their family.
The Whitlam years saw free university education for anyone that merited by high school (and equivilency) exams, health care has been universal - now with a split of both public and private, pharmacy companies are capped on their generics so that costs are reasonable, differences are picked up for those that can't afford medication (for almost all prescriptions), etc.
The Galactic Emperor is a monarchist, thankyouverymuch! And It treats all of Its loyal subjects quite well, with no discrimination against the water-based ones. Vs. if you have the misfortune to visit the Andromeda Galaxy...
On a something like a gas giant with a hydrogen atmosphere surrounding a rocky core, would it be possible for the vessel to be hydrogen breathing until it reaches the edge of space and then ignite a stage to carry it out of the gravity well? Or if a nitrogen or CO2 atmosphere is thick enough, to fly aerodynamically or even float until it reaches a point where the gravity is appreciably lower than at surface level?
On rocky planets gravity doesn't get much lower in the orbits we're concerned about. For example the ISS still experiences 90% of the gravity we experience at the surface. Reaching orbit is mostly about reaching a speed where the arc in which you are falling never intersects the surface.
But you can absolutely use an aircraft to gain height and speed, and then launch a much smaller rocket from that aircraft (where the speed is the primary advantage, and is what rockets use most of their fuel for). This setup is used by Virgin Galactic's SpaceShipTwo. There is also Virgin Orbit's LauncherOne, which is a small rocket that launches from a modified Boeing 747. On Earth it's just about not worth the additional complexity, but on planets with stronger gravity but comparable access to powered flight this might be the preferred method of reaching space.
One important factor might be the speed of sound. Subsonic flight is much easier for aircraft than supersonic flight. In an atmosphere with a much higher speed of sound, like say hydrogen, aircraft could reach much higher speeds and thus would be a much more advantageous launch platform for rockets. Assuming you already solved the issue of powering those planes of course.
But you can absolutely use an aircraft to gain height and speed, and then launch a much smaller rocket from that aircraft (where the speed is the primary advantage, and is what rockets use most of their fuel for). This setup is used by Virgin Galactic's SpaceShipTwo. There is also Virgin Orbit's LauncherOne, which is a small rocket that launches from a modified Boeing 747. On Earth it's just about not worth the additional complexity, but on planets with stronger gravity but comparable access to powered flight this might be the preferred method of reaching space.
One important factor might be the speed of sound. Subsonic flight is much easier for aircraft than supersonic flight. In an atmosphere with a much higher speed of sound, like say hydrogen, aircraft could reach much higher speeds and thus would be a much more advantageous launch platform for rockets. Assuming you already solved the issue of powering those planes of course.
I've never really understood this, why is it easier for a plane to reach that speed than a rocket? Is it sort of just another rocket stage?
An air-breathing jet engine doesn't need to carry oxidizer, which in a rocket is most of the propellant weight. It also has access to unlimited reaction mass, so it can be much more energy-efficient in producing thrust (it is more efficient to produce thrust by accelerating a lot of mass by a little, than by accelerating a little mass by a lot, but a rocket can't take advantage of this because it would need to carry all that extra mass. A plane can use ambient air for this purpose)
This all adds up to a plane needing to carry many times less mass to gain the same altitude and speed as a rocket, at least within relatively dense atmosphere.
This all adds up to a plane needing to carry many times less mass to gain the same altitude and speed as a rocket, at least within relatively dense atmosphere.
Is there a reason that there isn't a stage 0 to rockets that takes advantage of these properties?
A rocket on a typical orbital launch profile spends less than 60 seconds in air dense enough for jet engines to have good performance, so there is little to gain.
Pegasus is an orbital rocket launched from an aircraft, but it doesn't exactly impress with performance or cost-effectiveness. Just doesn't make much sense to operate a huge aircraft and design your system around it just to improve on the least important 10% of the flight.
Pegasus is an orbital rocket launched from an aircraft, but it doesn't exactly impress with performance or cost-effectiveness. Just doesn't make much sense to operate a huge aircraft and design your system around it just to improve on the least important 10% of the flight.
The basic physics of https://en.wikipedia.org/wiki/SABRE_(rocket_engine) have been vetted, which is an air breathing rocket engine. I don't know how much difference trying to liquify H2 vs O2 is though.
The oxygen is the majority of the mass (but not volume!) in a stoichiometric hydrogen engine, so the mass savings would be less I think. The RS-25 (space shuttle main engine) runs at a higher fuel ratio. Should work very similar to SABRE in general - the concept of a high speed atmosphere collector and precooler is pretty universal to any gas, and hydrogen has an extremely high heat transmission rate.
On a smaller gas giant you could build a floating platform (like a giant zeppelin) and launch from there. Because gas giants are so large the “surface” gravity at the altitude such a platform would be floating at is not as high as you might expect. On Uranus and Neptune it’s actually lower than 1G.
However, past Jupiter size the mass keeps increasing while the radius doesn’t, so even from a floating platform you’re contending with multiple G’s.
However, past Jupiter size the mass keeps increasing while the radius doesn’t, so even from a floating platform you’re contending with multiple G’s.
No. To float you would need a gas lighter than hydrogen, which isnt a thing. And powered flight (wings) without oxygen would be trickey, requiring more of a rocket motor than an aeroplane engine.
Yes, you could use a balloon filled with vacuum, but lifting something the size of an orbital rocket in a hydrogren atmosphere would require a vacuum chamber at least the size of a city, possibly the size of a small state. It would probably be easier to build a tower.
Yes, you could use a balloon filled with vacuum, but lifting something the size of an orbital rocket in a hydrogren atmosphere would require a vacuum chamber at least the size of a city, possibly the size of a small state. It would probably be easier to build a tower.
> No. To float you would need a gas lighter than hydrogen, which isnt a thing.
The atmosphere gets denser further down. You just need a negative pressure vessel, or to heat the hydrogen, like a hot air balloon. At 1 (Earth) atmospheric pressure the gravity of most Gas giants is quite low.
The atmosphere gets denser further down. You just need a negative pressure vessel, or to heat the hydrogen, like a hot air balloon. At 1 (Earth) atmospheric pressure the gravity of most Gas giants is quite low.
Sorry if I wasn't clear, but I brought up the question of floating with respect to nitrogen/CO2 atmospheres (thinking Titanlike or Venuslike) not hydrogen.
It's a moot point, but I still want to point out that "a gas lighter than hydrogen" is a thing: it is simply hydrogen at a higher temperature, i.e. a hot-hydrogen balloon, analogous to a hot-air balloon.
I do not want to ride in a hot hydrogen balloon :)
Why not? Hydrogen inside a hydrogen atmosphere is perfectly safe.
It's hydrogen inside an oxygen atmosphere that's the problem.
(So on Jupiter, you wouldn't want to ride in an oxygen balloon, ie you wouldn't want to ride in a hot air balloon there.)
It's hydrogen inside an oxygen atmosphere that's the problem.
(So on Jupiter, you wouldn't want to ride in an oxygen balloon, ie you wouldn't want to ride in a hot air balloon there.)
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Since it's barely mentioned in the answers, and was my first thought -- nuclear thermal rockets are something to think about too, at least in theory:
https://en.wikipedia.org/wiki/Nuclear_thermal_rocket
https://en.wikipedia.org/wiki/Nuclear_thermal_rocket
Not so much for takeoff! Most rocket designs better than chemical rockets trade off thrust for specific impulse. That's an improvement in orbit, since delta-v is delta-v. But imagine a 10kg rocket- it's receiving ~100N of gravity. If your engine doesn't put out 100N of thrust you'll just sit there on the launch pad. As you pick up speed you no longer have to deal with that (after all, LEO has basically the same gravity and doesn't have to burn against gravity at all) but when you're launching off something other than a point mass, some of your thrust has to go towards ensuring you don't hit the planet, or you will not into space today.
The practical designs we have for NTRs are solid core, which after long effort got up to a thrust to weight ratio of 7:1, meaning they could in principle carry up to 6 times their weight and accelerate up in Earth's gravity rather than down. Chemical rockets can get 70:1. No one ever had plans to use NTRs in lift platforms- instead they could serve as more efficient upper stage engines, for orbit-orbit transfer burns and the like. In principle there are engines which are technically NTR and offer much better performance, but no one's ever gotten a working prototype. Also you probably wouldn't want to launch with an open cycle rocket, since the open part describes how the radioactive fuel is ejected out the rear. Unfortunately, with the technology we have, we have to make tradeoffs between efficiency and thrust. For the lift stages chemical rockets are, for now, unrivaled.
(Unless of course your nuclear propulsion is of the more, shall we say, entertaining variety. Project Orion has its proponents...)
The practical designs we have for NTRs are solid core, which after long effort got up to a thrust to weight ratio of 7:1, meaning they could in principle carry up to 6 times their weight and accelerate up in Earth's gravity rather than down. Chemical rockets can get 70:1. No one ever had plans to use NTRs in lift platforms- instead they could serve as more efficient upper stage engines, for orbit-orbit transfer burns and the like. In principle there are engines which are technically NTR and offer much better performance, but no one's ever gotten a working prototype. Also you probably wouldn't want to launch with an open cycle rocket, since the open part describes how the radioactive fuel is ejected out the rear. Unfortunately, with the technology we have, we have to make tradeoffs between efficiency and thrust. For the lift stages chemical rockets are, for now, unrivaled.
(Unless of course your nuclear propulsion is of the more, shall we say, entertaining variety. Project Orion has its proponents...)
When discussing potential alien civilizations, one can’t discount the existence of civilizations which exist on substantially more radioactive planets.
If the background radiation of earth was 100x higher, would we care about an Orion launch? Or a small nuclear exchange…
If the background radiation of earth was 100x higher, would we care about an Orion launch? Or a small nuclear exchange…
The more fuel you have to pile onto the rocket, the less the weight of the engine matters.
Using the chart in the accepted answer, launching with chemical engines takes 50 thousand tons at 3x gravity and 3 million tons at 4x gravity.
Now consider a theoretical engine that has a 7:1 thrust to weight ratio at 1G but sips fuel. Take a 25 ton engine, strap 10 tons of fuel to it and 1 ton of payload. Watch it go to orbit on a single stage.
A real NTR doesn't save nearly as much fuel, but it can still be useful in certain ranges.
Using the chart in the accepted answer, launching with chemical engines takes 50 thousand tons at 3x gravity and 3 million tons at 4x gravity.
Now consider a theoretical engine that has a 7:1 thrust to weight ratio at 1G but sips fuel. Take a 25 ton engine, strap 10 tons of fuel to it and 1 ton of payload. Watch it go to orbit on a single stage.
A real NTR doesn't save nearly as much fuel, but it can still be useful in certain ranges.
I can't help but think that any species insane enough to use Orion drives in the first stage probably already found a way to blow itself up before it gets to that point.
And maybe I'm taking Terra Invicta too seriously but maybe they would wait until they figure out nuclear fusion and have more options.
And maybe I'm taking Terra Invicta too seriously but maybe they would wait until they figure out nuclear fusion and have more options.
I once got to briefly discuss project Orion with Freeman Dyson at a book signing. IIRC (it was a long time ago) he said that :
- he thought it could be made to work
- all big engineering projects (dams, skyscrapers etc) kill people
- putting all that radiation into the earth's atmosphere couldn't be justified
- he thought it could be made to work
- all big engineering projects (dams, skyscrapers etc) kill people
- putting all that radiation into the earth's atmosphere couldn't be justified
NTR is a very inefficient use of nuclear fuel. What you want is a NSWR:
https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket
A true nuclear rocket. Just like a chemical rocket is a controlled explosion, NSWR is a controlled (cough) nuclear explosion.
A true nuclear rocket. Just like a chemical rocket is a controlled explosion, NSWR is a controlled (cough) nuclear explosion.
NTR have high specific impulse but relatively low power to weight, this makes them good in space and poor for getting out of the gravity well as discussed here. They are efficient at using reaction mass but not for power to weight.
From the article:
Early publications were doubtful of space applications for nuclear engines. In 1947, a complete nuclear reactor was so heavy that solid core nuclear thermal engines would be entirely unable[23] to achieve a thrust-to-weight ratio of 1:1, which is needed to overcome the gravity of the Earth at launch. Over the next twenty-five years, U.S. nuclear thermal rocket designs eventually reached thrust-to-weight ratios of approximately 7:1. This is still a much lower thrust-to-weight ratio than what is achievable with chemical rockets, which have thrust-to-weight ratios on the order of 70:1.
From the article:
Early publications were doubtful of space applications for nuclear engines. In 1947, a complete nuclear reactor was so heavy that solid core nuclear thermal engines would be entirely unable[23] to achieve a thrust-to-weight ratio of 1:1, which is needed to overcome the gravity of the Earth at launch. Over the next twenty-five years, U.S. nuclear thermal rocket designs eventually reached thrust-to-weight ratios of approximately 7:1. This is still a much lower thrust-to-weight ratio than what is achievable with chemical rockets, which have thrust-to-weight ratios on the order of 70:1.
In Project Hail Mary one of the exoplanets is 8.45 Earth masses and the residents are able to attain space flight.
https://www.reddit.com/r/ProjectHailMary/comments/s5n7j4/eri...
https://www.reddit.com/r/ProjectHailMary/comments/s5n7j4/eri...
Wonderful book! One of my all time favorites. Though just cause they did in a book doesn't validate the science of doing it.
You're suggesting that Andy Weir did not science the shit out of that?
Well, he gave the aliens some hand-wave-y super-material called Xenonite.
Jazz hands!
The post about the 1.55R⊕ planet made me curious and I thought this was an interesting discussion
exe34(1)
By the time of the first orbital rocket, we had already discovered nuclear power. If chemical rockets were not capable of reaching orbit, a nuclear rocket was not far behind. Humans would probably already be on other planets if chemical rockets could not launch ICBMs because nuclear rocket technology would have continued to be advanced instead of abandoned.
Interest thoughts, but forgot one very practical calculation, unfortunately not easy to calculate. I say about shock-wave, which is known from practice on Earth, and for Earth limit rocket starting mass about 10k metric tonnes at sea level.
What it mean, shockwave from supersonic engine exhaust creates literally powerful pressure on construction, so on mentioned scale, nothing will withstand it long enough.
If it is possible to create much stronger materials, as I know at the moment, is unknown and we cannot forecast.
Sea level is important, because, at the moment I only remember TWO space rockets, which started from much different position, and high altitude (air) launch have very different atmosphere properties, which could be solution to shockwave problem (but have other limitations).
https://en.wikipedia.org/wiki/Northrop_Grumman_Pegasus https://en.wikipedia.org/wiki/LauncherOne
What it mean, shockwave from supersonic engine exhaust creates literally powerful pressure on construction, so on mentioned scale, nothing will withstand it long enough.
If it is possible to create much stronger materials, as I know at the moment, is unknown and we cannot forecast.
Sea level is important, because, at the moment I only remember TWO space rockets, which started from much different position, and high altitude (air) launch have very different atmosphere properties, which could be solution to shockwave problem (but have other limitations).
https://en.wikipedia.org/wiki/Northrop_Grumman_Pegasus https://en.wikipedia.org/wiki/LauncherOne
Vacuum-dwelling spherical cows are immune to shockwaves.
more depressing is that a space elevator might never see the day, since the material required for it is difficult to make
and even if it did exist, I have no idea how that thing would be put in place
if I remember, in the mars trilogy, it's assembled in high altitude, low gravity, and then put in place?
but gravity is lower on mars so rockets work better?
anyway, for earth, assembling a space elevator in space, meaning putting tough cable in orbit, would require so many launches and would emit a lot of CO2 in the process.
also the cable might be progressively thicker starting maybe at 1/3 of the distance, to bear the entire weight of the lower cable that is the most affected by gravity, while the rest of the cable would have a progressively centrifugal force away from earth to compensate, so maybe the cable would not need to be thick everywhere.
maybe that question was already asked
and even if it did exist, I have no idea how that thing would be put in place
if I remember, in the mars trilogy, it's assembled in high altitude, low gravity, and then put in place?
but gravity is lower on mars so rockets work better?
anyway, for earth, assembling a space elevator in space, meaning putting tough cable in orbit, would require so many launches and would emit a lot of CO2 in the process.
also the cable might be progressively thicker starting maybe at 1/3 of the distance, to bear the entire weight of the lower cable that is the most affected by gravity, while the rest of the cable would have a progressively centrifugal force away from earth to compensate, so maybe the cable would not need to be thick everywhere.
maybe that question was already asked
I have been pointing out for years that space elevators are feasible from a class of asteroid called a "fast rotator". They do not need to be very big either.
> and even if it did exist, I have no idea how that thing would be put in place
You put a platform in geosynchronous orbit and then lower a cable while raising a counterweight. The orbit of the entire structure is then balanced. The tricky part is lowering the bottom part through the atmosphere and securing the base.
You put a platform in geosynchronous orbit and then lower a cable while raising a counterweight. The orbit of the entire structure is then balanced. The tricky part is lowering the bottom part through the atmosphere and securing the base.
You can use active support to make a space elevator without super-materials. See https://en.wikipedia.org/wiki/Space_fountain
What technological advancements would be impossible for a civilization that can't go to space?
Those aliens have no gps and worse internet.
Flight travel and shipping is more expensive too.
Weather forecasting is more difficult.
They never create Starlink.
> and shipping
I want to mention that this would only be for heavier than air based airborne shipping. Liquid based shipping is unaffected by gravity. Archimedes' principle has the buoyancy force as the weight of the displaced liquid. The gravitational effects cancel out. Also, dirigibles would be possibly more useful here as, again, gravity cancels out.
Something neat I remembered, great comment all the same, thank you.
I want to mention that this would only be for heavier than air based airborne shipping. Liquid based shipping is unaffected by gravity. Archimedes' principle has the buoyancy force as the weight of the displaced liquid. The gravitational effects cancel out. Also, dirigibles would be possibly more useful here as, again, gravity cancels out.
Something neat I remembered, great comment all the same, thank you.
Internet is almost entirely terrestrial. GPS (for civilian use) could be replaced with a land-based network of transmitters (like GSM network).
Satellites mostly.
It’s easier to build a space elevator for a low gravity planet as well. So if some day we find a species living on a heavy earth, even throwing them a rope may be difficult.
Though I don’t suppose we’ll be visiting any aliens with chemical rockets regardless. We don’t have that kind of patience.
Though I don’t suppose we’ll be visiting any aliens with chemical rockets regardless. We don’t have that kind of patience.
I wonder if this was part of the inspiration for Outer Wilds, where the system’s planets are so small that they could be explored with wooden spaceships.
Um doesn’t balloon assistance become increasingly effective in that case? Use your plentiful surface energy blow up a balloon and float it up past the upper atmosphere.
But they explicitly exclude that from this question:
>For our purposes, let's not explore alternative or hybrid launch systems or boost systems (such as balloons, planes, laser beams, space elevators etc.). Just stick to chemical propellant rockets.
But they explicitly exclude that from this question:
>For our purposes, let's not explore alternative or hybrid launch systems or boost systems (such as balloons, planes, laser beams, space elevators etc.). Just stick to chemical propellant rockets.
Floating a balloon to the upper atmosphere doesn't make a meaningful difference in escaping the planet, it saves you a few percent of the energy but you still have to do most of the work to bring it up to escape velocity. Going to space isn't about getting high, it's about getting fast.
Though you might be able to get past a substantial portion of the atmosphere, and that would help you get past a lot of sources of friction.
Getting off a planet, even a heavy one, that doesn't have an atmosphere would be relatively easier, because you could 'just' build very long, flat rails to accelerate along.
Getting off a planet, even a heavy one, that doesn't have an atmosphere would be relatively easier, because you could 'just' build very long, flat rails to accelerate along.
I assume civilizations on heavier planets just use nuclear propelled rockets. As I understand it, the fuel density is so much higher that you could likely manage to build feasible nuclear rockets for far far higher g than you could chemical ones.
This thread made me curious, what's the most amount of stages a rocket has been launched with?
I'm guessing you mean stages to LEO, but technically Apollo was a six-stage rocket.
1. Saturn V first stage
2. Saturn V second stage
3. Saturn V third stage
4. Lunar module descent stage
5. Lunar module ascent stage
6. Service module for Earth return.
1. Saturn V first stage
2. Saturn V second stage
3. Saturn V third stage
4. Lunar module descent stage
5. Lunar module ascent stage
6. Service module for Earth return.
There are a couple of four-stage rockets. For example the Proton has a couple of four-stage variants, and India's primary workhorse, the PSLV, has four stages in all configurations.
Five stage rockets are a lot more exotic. There is the Minotaur V, which was launched exactly once, and India's ASLV, which they abandoned after a couple launches due to budget issues.
Five stage rockets are a lot more exotic. There is the Minotaur V, which was launched exactly once, and India's ASLV, which they abandoned after a couple launches due to budget issues.
https://en.wikipedia.org/wiki/Missile_Gap by Charlie Stross features this kind of concept.
By the same token, a space faring civilization based from the Moon or Mars is much more feasible, and a large argument for colonizing either imo, also rarely discussed nowadays.
Spacefaring would be much easier if we were Martians but going up, then down to colonize Mars just to start launching rockets back up from there seems mostly pointless? Isn't it much easier to colonize some asteroids, or Mars' moons?
[deleted]
The idea is that you can pick up cargo, fuel, and rocket-building minerals directly from Mars.
I wonder if air breathing rockets would change this much.
This was a delightfully weird question! I'm sure it makes sense to calculate this before landing on another planet, though.
Can't you like... put rocket on a rocket to shoot it out on orbit?
Can anyone ELI5 what the issue is; I understand/assume larger Earth increases gravity so more for rocket to overcome, but why doesn't that also affect jet aeroplanes?
Or does it, it's just that this is space.SE so naturally they're asking about rockets specifically?
Or does it, it's just that this is space.SE so naturally they're asking about rockets specifically?
Planes get lift from the pressure difference between top and bottom of the plane.
A higher gravity planet pulls harder on air, increasing the pressure from any given mass over any given area, which IIRC doesn't affect this difference directly.
Indirectly, a higher density atmosphere (which is technically a different question to pressure; look at Venus for example), will lead to higher drag, needing more engine thrust to maintain any given speed. Lift depends on speed, but is easier to design around.
A higher gravity planet pulls harder on air, increasing the pressure from any given mass over any given area, which IIRC doesn't affect this difference directly.
Indirectly, a higher density atmosphere (which is technically a different question to pressure; look at Venus for example), will lead to higher drag, needing more engine thrust to maintain any given speed. Lift depends on speed, but is easier to design around.
> but why doesn't that also affect jet aeroplanes?
Jet engines pull in air and expel it out the back, creating thrust. The energy to do so comes from fuel, but almost all of the reaction mass is air.
Rockets don't have this luxury; they must bring all the reaction mass with them. This causes a big problem of diminishing returns. Adding more fuel means you can burn longer, but also makes the rocket heavier so it doesn't accelerate as much with the same thrust.
The result is that the fuel required goes up exponentially with the desired delta-v, as expressed by the rocket equation .
Jet engines pull in air and expel it out the back, creating thrust. The energy to do so comes from fuel, but almost all of the reaction mass is air.
Rockets don't have this luxury; they must bring all the reaction mass with them. This causes a big problem of diminishing returns. Adding more fuel means you can burn longer, but also makes the rocket heavier so it doesn't accelerate as much with the same thrust.
The result is that the fuel required goes up exponentially with the desired delta-v, as expressed by the rocket equation .
if reaching escape speed is impossible, building a work rocket is impossible.
Now try being from a water planet, and getting to escape velocity!
You can escape any gravity with teleportation, but it's easier said than done.
Or maybe we're just a dumb civilization/species? Maybe it's also dumb to assume our intelligence is "normal".
Or maybe we're just a dumb civilization/species? Maybe it's also dumb to assume our intelligence is "normal".
If Randall Munroe's name is not on the answer, it's not the answer.
Unless you are in a black hole you can get off any planet theoraatally
And now let’s break all the numbers by mentioning it’s likely the aliens are not dumb enough to make rockets so inefficient for their task. Nuclear at minimum would be used.
Do you have an explanation for how nuclear would actually be better? As far as I understand it’s terrible for orbital insertion levels of thrust.
It was a nice surprise (and a relief) to the early rocket pioneers to realize that we lived on a planet where gravity and chemistry would make orbital rockets possible. The rest was just engineering.