Sky skimmers: The race to fly satellites at the lowest orbits yet(bbc.com)
bbc.com
Sky skimmers: The race to fly satellites at the lowest orbits yet
https://www.bbc.com/future/article/20250207-sky-skimmers-the-race-to-send-satellites-into-very-low-earth-orbits
80 comments
> In order to produce thrust, it has to exit the back of the satellite at a significantly higher speed.
Why? It can exit at 1 m/s and still be thrust. And as long as momentum from engine pushing is larger than momentum of stopping atmosphere -- it will accelerate.
In other words -- chemical engines have exit speeds way lower than 8 km/s, but are able to accelerate spaceships to and above 8 km/s.
Why? It can exit at 1 m/s and still be thrust. And as long as momentum from engine pushing is larger than momentum of stopping atmosphere -- it will accelerate.
In other words -- chemical engines have exit speeds way lower than 8 km/s, but are able to accelerate spaceships to and above 8 km/s.
I suppose because they are catching them when they are at ~0m/s in the atmosphere so they're worth -8km/s worth of momentum to begin with. So you would have to fire them out a >8km/s to get a net +ve change in momentum.
> It can exit at 1 m/s and still be thrust
But it won't be enough thrust to counterbalance the force of scooping up air that collides at 8 km/s
In order to produce net thrust, it has to be more than that.
But it won't be enough thrust to counterbalance the force of scooping up air that collides at 8 km/s
In order to produce net thrust, it has to be more than that.
The mass of propellant being expelled is many times higher than the mass of air colliding with the rocket.
If that is the case then yes, agree, but there was no indication that is the case. The air is very thin out there.
In fact, it's linearly proportional, because momentum us m*v, so for 20 km/s propellant exhaust seed and 8 km/s air it needs to spend exactly 8/20=0.4 times the propellant to not slow down.
In fact, it's linearly proportional, because momentum us m*v, so for 20 km/s propellant exhaust seed and 8 km/s air it needs to spend exactly 8/20=0.4 times the propellant to not slow down.
I understood that they want to used scoop up air to use as propellant. Only a fraction of the air it encounters will be able to be sucked in by the rocket.
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I would suspect that the conditions behind the VLEO satellite are close enough to a vacuum that vacuum chamber results are actually relevant.
Getting to ultra high vacuum like in higher orbits requires a multistage vacuum pump. To get the right conditions for VLEO they only need to skip the final stage turbomolecular vacuum pump or run it slower to decrease its effectiveness - it's basically just a bunch of fan blades that use transfer of momentum to bump molecules out of the vacuum chamber and keep them out.
I think the harder part is simulating the relative velocities of the molecules of air. They can try to use the same mechanism as a turbomolecular pump to accelerate the remaining molecules at the test setup, but AFAIK the maximum velocities in a turbomolecular pump are on the order of 1km/s, not 8km/s like in VLEO. Quick back of the napkin math says it'd need tip velocities of 4km/s which translates to over 380,000 RPM with a 4 in blade radius. I'm not sure there any materials capable of withstanding those forces. At 0.5m diameter it's a more reasonable ~76,000 RPM but that's basically the size of a commercial jet engine that probably caps out at 10-20,000 RPM.
I think the harder part is simulating the relative velocities of the molecules of air. They can try to use the same mechanism as a turbomolecular pump to accelerate the remaining molecules at the test setup, but AFAIK the maximum velocities in a turbomolecular pump are on the order of 1km/s, not 8km/s like in VLEO. Quick back of the napkin math says it'd need tip velocities of 4km/s which translates to over 380,000 RPM with a 4 in blade radius. I'm not sure there any materials capable of withstanding those forces. At 0.5m diameter it's a more reasonable ~76,000 RPM but that's basically the size of a commercial jet engine that probably caps out at 10-20,000 RPM.
I know more about turbines then I do vacuum pumps, and do agree that about 1000 m/s tip velocity is pretty much the material limit. I suppose something like the solid disc in a tesla turbine might exceed that however I don't know if that's useful or if you'll get even close to 8km/s out of that.
Going beyond spinning discs there's the USAFs "Hypervelocity Wind Tunnel 9", that can hit mach 14 or 4800 m/s, which, still not good enough.
Going beyond spinning discs there's the USAFs "Hypervelocity Wind Tunnel 9", that can hit mach 14 or 4800 m/s, which, still not good enough.
Turbomolecular pumps are basically turbines except they’ve got more blades in a different configuration, they’re driven by a motor instead of extracting energy, they have no method for convective cooling, and can’t use any lubricants or cooling fluid because they would vaporize and contaminate the vacuum.
I’ve got more experience with turbojet engines than turbines so I’m not sure how that changes the calculus on the last two points. Turbomolecular pumps use active electromagnetic bearings and require very precise manufacturing to match blade radius with the chassis and balance the blades. The material science for the blades is mostly the same.
I’m sure they’d could get plenty of useful data at mach 14 but sadly I doubt the USAF wind tunnel machinery would work in a vacuum environment without melting immediately, and it’s probably way bigger than even the biggest vacuum chambers NASA has. I’ve never heard of the tesla turbine before so I don’t know how the angular momentum translates to the molecules.
I’ve got more experience with turbojet engines than turbines so I’m not sure how that changes the calculus on the last two points. Turbomolecular pumps use active electromagnetic bearings and require very precise manufacturing to match blade radius with the chassis and balance the blades. The material science for the blades is mostly the same.
I’m sure they’d could get plenty of useful data at mach 14 but sadly I doubt the USAF wind tunnel machinery would work in a vacuum environment without melting immediately, and it’s probably way bigger than even the biggest vacuum chambers NASA has. I’ve never heard of the tesla turbine before so I don’t know how the angular momentum translates to the molecules.
Presumably you'd have an array of 'slow' ion thrusters upstream of your test article in your vacuum chamber to generate your flow. Matching temperature and velocity profile exactly is probably fairly tricky, but producing nominally 8km/s of very dilute gas shouldn't be particularly difficult.
I suppose something like the solid disc in a Tesla turbine might exceed that
It’s been a few years since I studied these types of issues, but I assume the relevant mechanical deformation from these speeds (creep) is a problem no matter the geometry.
It’s been a few years since I studied these types of issues, but I assume the relevant mechanical deformation from these speeds (creep) is a problem no matter the geometry.
- "The other major application of being in VLEO is that you are closer to the ground for communications. That is particularly useful for space internet services, like SpaceX's Starlink network, which currently beams the internet to receivers on the ground from higher orbits. By using lower satellites in VLEO, the antennas can act like mobile phone towers and beam the internet straight to your phone. "Going direct to a cell phone is a challenging task to do from space," says Tim Farrar, a satellite communications expert in California. "These lower [orbits] could enable a direct-to-cell constellation."
Starlink direct-to-cell satellites are already in a VLEO orbit shell, distinct from the rest of the constellation. They use electric propulsion (like all Starlinks) to counter drag, though it is not air-breathing electric propulsion (the theme of the OP).
- "The higher luminosity of these DTCs compared to regular Starlinks is partly because they circle Earth at just 217 miles (350 kilometers) above the surface, which is lower than traditional Starlink internet satellites, whose altitude is 340 miles (550 kilometers), the study reported. [...] There are now over 100 DTC satellites in low Earth orbit, including 13 that were launched last week. Following successful testing of the first batch of DTCs, in March SpaceX requested an amendment to their license with the U.S. Federal Communications Commission that would allow them to operate up to 7,500 DTCs in LEO."
https://www.space.com/spacex-starlink-direct-to-cell-satelli...
Starlink direct-to-cell satellites are already in a VLEO orbit shell, distinct from the rest of the constellation. They use electric propulsion (like all Starlinks) to counter drag, though it is not air-breathing electric propulsion (the theme of the OP).
- "The higher luminosity of these DTCs compared to regular Starlinks is partly because they circle Earth at just 217 miles (350 kilometers) above the surface, which is lower than traditional Starlink internet satellites, whose altitude is 340 miles (550 kilometers), the study reported. [...] There are now over 100 DTC satellites in low Earth orbit, including 13 that were launched last week. Following successful testing of the first batch of DTCs, in March SpaceX requested an amendment to their license with the U.S. Federal Communications Commission that would allow them to operate up to 7,500 DTCs in LEO."
https://www.space.com/spacex-starlink-direct-to-cell-satelli...
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Defining VLEO at 220km seems dumb. The ISS survives perfectly fine on periodic boosts.
Why not just a large constellation of weather balloons with a satellite payload? You have to deal with wind patterns, but that's probably a solvable problem with enough of them. Much cheaper to launch and they don't regularly and necessarily burn to ashes!
A VLEO satellite orbits the earth in under two hours, giving it visual coverage of the planet along the satellite ground track for a dozen or more orbits per day. Launching enough balloons to get that kind of coverage, especially without the ability to control their position would cost an astronomical amount. You're not going to get anywhere near the same coverage and they'll probably all end up blown by the same wind system into a vortex and get stuck there anyway.
Weather balloons are inexpensive because the radiosonde payload is very cheap and light, not requiring much power or other infrastructure. Putting a proper surveillance payload on it would dramatically increase the price mostly because it'd then have to power the payload. That role is currently mostly done by UAVs.
Weather balloons are inexpensive because the radiosonde payload is very cheap and light, not requiring much power or other infrastructure. Putting a proper surveillance payload on it would dramatically increase the price mostly because it'd then have to power the payload. That role is currently mostly done by UAVs.
Nope!
Weirdly, I'm probably the one person who's worked extensively with both paradigms...
There are several players in the balloon market spinning up. It's becoming very hot very fast.
The balloons in question are much smarter that radiosondes now. They are fully capable of autonomous navigation within certain limits and can even orbit a point for days at a time via some clever weather mechanics. They're also very easy to launch. Two guys and a truck can launch over a dozen in a day and they're all aggregated and flown remotely via various links.
On the payload side it's actually much easier to do optics on a balloon, you have all the same pressure and thermal issues as space but you can iterate much faster when your cost to first pixels is thousands instead of tens of millions for the same ground resolution (GSD, drives necessary aperture size). I'm not going to spell out the details on either because that's the secret sauce that pays my mortgage but it suffices to say, if you're 10x lower, you need a lens that weights a little less. It's also worth noting that a VLEO sat will only be overhead for a few minutes, balloons can stream live video as long as you want, right now (no future tech or constellations needed).
The class of UAV that can begin to compete with a balloon is two to three orders of magnitude more expensive and still has nowhere near the endurance.
There are also other sensors and phenomenologies that are wildly more capable on a balloon platform than any type of satellite or UAV but I'll get yelled at if I spell any of those out...
Weirdly, I'm probably the one person who's worked extensively with both paradigms...
There are several players in the balloon market spinning up. It's becoming very hot very fast.
The balloons in question are much smarter that radiosondes now. They are fully capable of autonomous navigation within certain limits and can even orbit a point for days at a time via some clever weather mechanics. They're also very easy to launch. Two guys and a truck can launch over a dozen in a day and they're all aggregated and flown remotely via various links.
On the payload side it's actually much easier to do optics on a balloon, you have all the same pressure and thermal issues as space but you can iterate much faster when your cost to first pixels is thousands instead of tens of millions for the same ground resolution (GSD, drives necessary aperture size). I'm not going to spell out the details on either because that's the secret sauce that pays my mortgage but it suffices to say, if you're 10x lower, you need a lens that weights a little less. It's also worth noting that a VLEO sat will only be overhead for a few minutes, balloons can stream live video as long as you want, right now (no future tech or constellations needed).
The class of UAV that can begin to compete with a balloon is two to three orders of magnitude more expensive and still has nowhere near the endurance.
There are also other sensors and phenomenologies that are wildly more capable on a balloon platform than any type of satellite or UAV but I'll get yelled at if I spell any of those out...
Saving this for another round of 'UFO sightings' panic.
There was recently an article about the 'UFOs' actually being 'just' Chinese balloons designed to record everything about the radars poking them to learn about capabilities of US defense systems (including F-35 in action). Guess we'll see more of them soon.
There was recently an article about the 'UFOs' actually being 'just' Chinese balloons designed to record everything about the radars poking them to learn about capabilities of US defense systems (including F-35 in action). Guess we'll see more of them soon.
I've seen various balloons more or less constantly spook the UFO people. There are a few designs that don't look like a traditional balloon so everyone thinks they're some sort of cloaking field or something
Found it - this one is worse. Army pilots fear being accused of 'seeing UFO', so they underreport Chinese spy balloons, which then probe US defense systems:
https://www.twz.com/40054/adversary-drones-are-spying-on-the...
Are you in Europe? Are there any promising European companies in this space? I’ve been thinking that something like this would be perfect in Europe going forward. Could help de-risk both reliance on subsea comms cables, US constellations and addresses the (comparative) lack of capital.
I don’t think he’s in Europe. Who will fund such risky venture or buy services from a company in there. Ballons however are very good for transport of cigarettes over the border of Belarus into EU. Cigarettes are light and the balloons from China cheap.
All the companies I know of are US based. That said if you know what you're doing it's much lower risk than a satellite venture
Are you staying under the 12-pound ICAO-limit for a payload (which must be split into two packages)? If so, how much power is continuously available to the payload and how long can each balloon stay aloft?
That info would strangely enough dox me/be a trade secret but there are companies doing both exempt and non exempt, and both have GSD better than any commercial satellite
Thanks for the reply. Are you able to comment a bit more on the costs. I’m particularly curious about your statement about balloons being orders of magnitude less expensive than satellites. Does that mean 1/1000 the cost or 1/100 the cost? I ask because LEO satellites with usable power (50W) no longer cost millions, or even a single million to put on orbit. And they have operational lifespans of 5 years.
I'm talking all up costs (cost to first pixels), so the cost to acquire a bus and payload then launch it vs buy a balloon with an imager payload and release it. Any comparable satellite right now is likely closer to hundreds of millions just due to necessary aperture size. A balloon launch for an imagery collect will run you under 30k all in, and you can reuse most of the system after you recover it.
LEO is cheap but you need a massive aperture, measured in meters, to get equivalent GSD to even the crappiest balloon imager, so the price tag suddenly jumps. These aren't cubesats, they're suddenly the size of a bus, see Worldview Legion for a recent comparison, and it has a much worse nadir GSD than balloons.
VLEO is still extremely expensive because you need a very robust propulsion system and there are other design considerations like atomic oxygen corrosion. The optics to match a balloon also put you into the mini-fridge to refrigerator sized optics assembly class which means while you can rideshare, it's not cheap to build or launch, see Albedo space:
https://albedo.com/post/upcoming-launch-of-clarity-1-and-alb...
Also the regulatory issues are still massive, you need to get a NOAA license for imagery and once you go under a certain GSD limit they become very difficult to obtain.
LEO is cheap but you need a massive aperture, measured in meters, to get equivalent GSD to even the crappiest balloon imager, so the price tag suddenly jumps. These aren't cubesats, they're suddenly the size of a bus, see Worldview Legion for a recent comparison, and it has a much worse nadir GSD than balloons.
VLEO is still extremely expensive because you need a very robust propulsion system and there are other design considerations like atomic oxygen corrosion. The optics to match a balloon also put you into the mini-fridge to refrigerator sized optics assembly class which means while you can rideshare, it's not cheap to build or launch, see Albedo space:
https://albedo.com/post/upcoming-launch-of-clarity-1-and-alb...
Also the regulatory issues are still massive, you need to get a NOAA license for imagery and once you go under a certain GSD limit they become very difficult to obtain.
What's the longevity of such balloons? Don't they burst or leak?
Right now they fly for months, but years is possible with the right design.
The can sometimes leak slightly but they make up for it by dispensing small amounts of ballast material.
The can sometimes leak slightly but they make up for it by dispensing small amounts of ballast material.
Yup, I've worked on both and the balloons are generally just better platforms given current constraints. They can actually be steered rather accurately, if you're ever bored go look at the ADSB logs of the Aerostar balloons, they regularly can be found wandering the country and if you look at the altitude history you can start to see how they work.
They're generally more environmentally friendly too, worst case you have to go ask a farmer to retrieve the thing out of their field.
They're generally more environmentally friendly too, worst case you have to go ask a farmer to retrieve the thing out of their field.
> and they don't regularly and necessarily burn to ashes!
_In principle_, a VLEO satellite could stay up forever (or, well, realistically until the engine wore out).
Weather balloons also don't last forever.
_In principle_, a VLEO satellite could stay up forever (or, well, realistically until the engine wore out).
Weather balloons also don't last forever.
There are atomic oxygen issues for VLEO sats, the front of the satellite slowly corrodes away from the impacts. They're longer lived than current balloons but mission lifetimes more than low single digit years aren't really feasible right now.
Alas, not the tropopause-skimming Solid Osmium Sphere Satellite.
https://www.researchgate.net/publication/326153433_The_edge_...
https://www.researchgate.net/publication/326153433_The_edge_...
This also has the benefit of guaranteeing that your rocket's second stage will be deorbited in a timely manner.
When asked for use cases, they give a bunch of niche things like wildfire monitoring. What is the actual market for this stuff? Is it all spy satellites? Better versions of Street View?
Besides niche scientific applications, this is mostly about extremely large constellations.
The classic LEO, roughly 500km-1000km, is already quite full, and placing a lot of new satellites there increases the risk of triggering a chain reaction of collisions with orbital debris (Kessler syndrome). At these altitudes the atmosphere is thin enough that even small pieces of debris are long-lived, thus potentially creating a long-term problem for all kinds of human and non-human spaceflight.
In the VLEO band, on the other hand, the thicker atmosphere makes maintaining orbit more difficult, but also makes debris very short-lived. Due to this, it may be reasonable to risk placing a million-satellite communications network somewhere between 200-300km, which would be utterly impossible further up. Data rates, latency, mesh size, etc. also improve of course.
The classic LEO, roughly 500km-1000km, is already quite full, and placing a lot of new satellites there increases the risk of triggering a chain reaction of collisions with orbital debris (Kessler syndrome). At these altitudes the atmosphere is thin enough that even small pieces of debris are long-lived, thus potentially creating a long-term problem for all kinds of human and non-human spaceflight.
In the VLEO band, on the other hand, the thicker atmosphere makes maintaining orbit more difficult, but also makes debris very short-lived. Due to this, it may be reasonable to risk placing a million-satellite communications network somewhere between 200-300km, which would be utterly impossible further up. Data rates, latency, mesh size, etc. also improve of course.
Lower latency communications snd more detailed Earth observation
Comms would be the big commercial one; latency reduction relative to LEO systems. High detail earth observation is also useful for weather stuff.
Perhaps real time flood water monitoring?
Despite advancements in technology, as on today it is not possible to get near real time information of flooding.
Despite advancements in technology, as on today it is not possible to get near real time information of flooding.
Phone to satellite communication.
> Theoretically, if you can generate a thrust that is the same as your drag
Is it just me or does that make no sense at all. Surely the friction will always be significant higher.
So at best such tech lets you go a little lower not go near indefinitely as article suggests. Sorta like how an energy recovery system extends a cars range
Is it just me or does that make no sense at all. Surely the friction will always be significant higher.
So at best such tech lets you go a little lower not go near indefinitely as article suggests. Sorta like how an energy recovery system extends a cars range
Because it is using power from solar panels to accelerate the ions, that's what makes it not a perpetual motion machine. We know we can build ion thrusters that generate enough thrust to overcome the drag at these orbits. But that is with different propellant. The question is if you can do the same using air as the propellant, and with even higher thrust to account for the additional drag a scoop would have over an aerodynamic design.
I suppose solar powered aircraft count as perpetual motion machines in OP's books. They categorically aren't. :)
https://en.wikipedia.org/wiki/Solar-powered_aircraft
https://en.wikipedia.org/wiki/Solar-powered_aircraft
The air molecules used by the ion engine as propellant go through channels in the satellite. The molecules aren't "caught" but instead pass through it and once they're ionized, the electromagnetic repulsion between the propellant and the satellite pushes them apart.
As long as the solar panels can supply enough energy, I don't see a problem. It isn't actually a perpetual motion machine as there's a constant energy input and there's no violation of conservation of momentum that I can see. The problem I think is more of an optimization - how big can they make the solar panels without adding too much drag? That will set a bound for how low these things can fly.
As long as the solar panels can supply enough energy, I don't see a problem. It isn't actually a perpetual motion machine as there's a constant energy input and there's no violation of conservation of momentum that I can see. The problem I think is more of an optimization - how big can they make the solar panels without adding too much drag? That will set a bound for how low these things can fly.
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Universe Today has a great interview on this tech. Even optimistically, it's knifes edge, just barely enough margin to keep things going before factoring in things like solar storms.
Why would friction always be higher? In principle, this is just like an electric RC plane. You use the surrounding air for propulsion while keeping your own mass constant.
Not sure if it's a good idea to pollute even more orbits. We're basically one low-iq billionaire fuck-up away from creating a barrier of shrapnel around the planet.
I like how the article glazes over the fact that this is drone swarm delivery tech. You are naive to think otherwise.
What kind of drones are you thinking, other than just good ol' missiles?
Anything even remotely drone shaped would have to be covered in so many aerogel reentry tiles and thermal insulation I'm not sure there would be any usable weight left for a payload.
Anything even remotely drone shaped would have to be covered in so many aerogel reentry tiles and thermal insulation I'm not sure there would be any usable weight left for a payload.
Why would I want a drone swarm in VLEO? That seems like a really hard place to effectively use drones from compared to pretty much any alternative.
Quick deployment into a battlefield or disaster zone anywhere on earth is one idea.
Connection, remote sensing, and mesh networking are useful.
Connection, remote sensing, and mesh networking are useful.
There is no difference between these and higher satellites. It still super expensive to get them down because have to stop orbital speed. If anything, VLEO is worse cause they are going faster. Not to mention the cost of getting into space in first place. Plus, need lots of satellites to support dropping things anywhere on world.
Also, it is rare to have anything that needs 30 min response time. Most things can be handled by local resources or wait for an airplane. Good example is that the US is working on hypersonic missiles and deploying them around the world.
Also, it is rare to have anything that needs 30 min response time. Most things can be handled by local resources or wait for an airplane. Good example is that the US is working on hypersonic missiles and deploying them around the world.
CubeSats are certainly useful, but Starlink, Planet, and Maxer are expensive to position just right.
VLEO has its uses.
VLEO has its uses.
You are missing the forest for the trees. This is an aerospace vehicle capable of flying in the air indefinitely. How many drones can you fit on a vehicle? How many vehicles can you fly at once? 60 miles is already reachable by the cheapest and most deadly weapon class of short-range drones. And now all they need to do is fall down. At freefall that is 140 seconds until it reaches the ground.
You come across as fairly confrontational.
But I don’t understand the point. Satellites already fly indefinitely and can drop payloads of kinetic energy weapons. Why all the complexity of VLEO and drones? What could you that’s impossible with other, simpler, already-extant weapons systems?
But I don’t understand the point. Satellites already fly indefinitely and can drop payloads of kinetic energy weapons. Why all the complexity of VLEO and drones? What could you that’s impossible with other, simpler, already-extant weapons systems?
> Why all the complexity of VLEO and drones? What could you that’s impossible with other, simpler, already-extant weapons systems?
Assuming the tech works, you can move the sat to any orbital plane, making it significantly harder for an adversary to track all of your vleo assets.
Assuming the tech works, you can move the sat to any orbital plane, making it significantly harder for an adversary to track all of your vleo assets.
I am voicing my opinion in which I believe in strongly, nothing more.
https://www.youtube.com/watch?v=TlO2gcs1YvM
https://www.youtube.com/watch?v=TlO2gcs1YvM
We already have fully autonomous space drone swarms armed with nuclear warheads, we just keep them underground/underwater because...humans are weird.
I mean... okay, but no matter how much you believe in it, it doesn't make any sense. This would offer no advantage over conventional satellites for this application (ie it would be similarly terrible for it).
Are you thinking of something like this? https://en.wikipedia.org/wiki/Kinetic_bombardment#2003_Unite...
Again, you probably wouldn't bother with VLEO for that, too much extra complexity with no obvious advantage vs VLEO.
Are you thinking of something like this? https://en.wikipedia.org/wiki/Kinetic_bombardment#2003_Unite...
Again, you probably wouldn't bother with VLEO for that, too much extra complexity with no obvious advantage vs VLEO.
The drones would burn up. The satellites are in space and moving at space speeds. If the satellite drops anything, it stays in orbit and slowly decays. Dropping anything requires a large rocket to get out of orbit. The payload would still be going fast and deal with re-entry.
Also, the article doesn't say that they are at 60mi, just that VLEO goes down to 60mi. The satellites are likely to be higher because there is less drag.
Also, the article doesn't say that they are at 60mi, just that VLEO goes down to 60mi. The satellites are likely to be higher because there is less drag.
> And now all they need to do is fall down.
That's, ah, a huge 'all' :) They'd be moving at about 8-10 kilometres per second. The vehicle is not _really_ 'flying in the air', it just looks a bit like that. It's in orbit at terrifying speeds. Your 'drones' would require very extensive heat shielding. They would not be at all cheap. And why use this rather than a normal, cheaper, less complex LEO satellite? Or an ICBM. If you want to arbitrarily drop heavily shielded gadgets on someone's head at silly speeds, the normal tool is an ICBM (the gadgets usually contain a nuke, not a drone, mind you).
That's, ah, a huge 'all' :) They'd be moving at about 8-10 kilometres per second. The vehicle is not _really_ 'flying in the air', it just looks a bit like that. It's in orbit at terrifying speeds. Your 'drones' would require very extensive heat shielding. They would not be at all cheap. And why use this rather than a normal, cheaper, less complex LEO satellite? Or an ICBM. If you want to arbitrarily drop heavily shielded gadgets on someone's head at silly speeds, the normal tool is an ICBM (the gadgets usually contain a nuke, not a drone, mind you).
It doesn't seem terribly practical as one? The 'drones' would still have to re-enter, at, well, impressive speed. So you're not talking about terribly practical drones; more something like an ICBM warhead.
Even if this were practical, why use weird expensive highly-visible VLEO satellites rather than conventional LEO satellites? I can't see what advantage the VLEO stuff would give you here.
Even if this were practical, why use weird expensive highly-visible VLEO satellites rather than conventional LEO satellites? I can't see what advantage the VLEO stuff would give you here.
Based.
As long as "based" is taken to mean "confidently wrong", yeah.
Based af
Based af
Something that bothered me, until I looked up some numbers: the air a VLEO satellite scoops up is presumably more or less at rest wrt the Earth below it--there could be wind and effects of the Earth's magnetic field, and so forth, but for practical purposes it would be coming at the VLEO satellite at about 18,000 mph, or 8 km/s. In order to produce thrust, it has to exit the back of the satellite at a significantly higher speed. It turns out that ion thrusters have an exit speed of 20--50 km/s. So I guess it's feasible.
More info in this Wikipedia article: https://en.wikipedia.org/wiki/Atmosphere-breathing_electric_... --which says the exit speed of this kind of ion thruster is 55 km/s (as tested in a vacuum chamber).