First firing of air-breathing electric thruster(esa.int)
esa.int
First firing of air-breathing electric thruster
http://www.esa.int/Our_Activities/Space_Engineering_Technology/World-first_firing_of_air-breathing_electric_thruster
123 comments
This is still very much sci-fi at the moment for anything flying above a 250 km earth orbit because atmospheric density decreases dramatically fast with altitude.
The missions targeted by this technology are GOCE-like spacecrafts which by design must fly low and need an insane amount of propellant to compensate for the high atmospheric drag at such altitude.
The missions targeted by this technology are GOCE-like spacecrafts which by design must fly low and need an insane amount of propellant to compensate for the high atmospheric drag at such altitude.
> This is still very much sci-fi at the moment for anything flying above a 250 km earth orbit because atmospheric density decreases dramatically fast with altitude.
One of my favorite takes on this concept was Poul Anderson's Tau Zero [1], which used a Bussard ramjet [2]. Apparently, in the 70s, in was thought that there was enough hydrogen surrounding our solar system to support interstellar travel.
[1] https://en.wikipedia.org/wiki/Tau_Zero
[2] https://en.wikipedia.org/wiki/Bussard_ramjet
One of my favorite takes on this concept was Poul Anderson's Tau Zero [1], which used a Bussard ramjet [2]. Apparently, in the 70s, in was thought that there was enough hydrogen surrounding our solar system to support interstellar travel.
[1] https://en.wikipedia.org/wiki/Tau_Zero
[2] https://en.wikipedia.org/wiki/Bussard_ramjet
Tau Zero should be better known. I read it again recently after many years, I couldn't put it down. It's a pity that more real histories don't end like this:
"I sure as hell can. Once a crisis is past, once people can manage for themselves ... what better can a king do for them than take off his crown?"
"I sure as hell can. Once a crisis is past, once people can manage for themselves ... what better can a king do for them than take off his crown?"
Somewhat related is the E-sail [1] concept, a perhaps less ambitious but (probably) feasible idea to harness the momentum of solar wind particles with very long charged wires.
[1] https://en.wikipedia.org/wiki/Electric_sail
[1] https://en.wikipedia.org/wiki/Electric_sail
A personal favorite feature on federation vessels.
http://memory-alpha.wikia.com/wiki/Bussard_collector
http://memory-alpha.wikia.com/wiki/Bussard_collector
How can you decelerate with a ramjet? Wouldn't your own exhaust push the matter you needed out of the way?
You could push the exhaust single-file in a highly focused beam, leaving most of the solid angle around you unpushed.
Bussard Ramjets can be useful for interstellar travel. The net thrust is not great, but for very long and relatively slow trips it let's you power a very large ship without dragging along as much fuel assuming you can get hydrogen only fusion to work.
People who have looked at particular instances of fusion-powered ramjets have found that they don't produce enough thrust to overcome drag:
https://en.wikipedia.org/wiki/Bussard_ramjet
More recent thinking on the concept has centered around magsails which turn the drag into a good thing. Decelerating a starship is an even tougher problem than accelerating one, and magsails are a great choice for that. (And might even be able to get a speed of 0.2% of light for departure on the solar wind)
https://en.wikipedia.org/wiki/Bussard_ramjet
More recent thinking on the concept has centered around magsails which turn the drag into a good thing. Decelerating a starship is an even tougher problem than accelerating one, and magsails are a great choice for that. (And might even be able to get a speed of 0.2% of light for departure on the solar wind)
You need fuel for more than just propulsion. A hybrid engine that provides trust to offset the drag while also powering a ship is very viable.
Remember, drag is a function of relative speeds. A hypothetical example with zero velocity would allow you to gather fuel without any drag.
Now for a very large and 'slow' generation ship you need a lot of energy to keep the crew alive, able to manufacture repair parts, keep the lights on etc. Now, say you want need 1 ounce of fuel per hour that does not seem bad but if your talking a 100,000+ year trip that's 54+ million pounds.
Sure, that kind of trip does not seem appealing, but remember taking 4x the mass at 1/2 the speed takes the same energy. Further you are going to want to bootstrap a civilization at the other end which means outside of grey goo taking a lot of stuff. With the added benefit of being able to go somewhere else.
PS: You also get more energy from hydrogen the further up the chain you go. A multi stage reactor that's spitting out lead provides more energy.
Remember, drag is a function of relative speeds. A hypothetical example with zero velocity would allow you to gather fuel without any drag.
Now for a very large and 'slow' generation ship you need a lot of energy to keep the crew alive, able to manufacture repair parts, keep the lights on etc. Now, say you want need 1 ounce of fuel per hour that does not seem bad but if your talking a 100,000+ year trip that's 54+ million pounds.
Sure, that kind of trip does not seem appealing, but remember taking 4x the mass at 1/2 the speed takes the same energy. Further you are going to want to bootstrap a civilization at the other end which means outside of grey goo taking a lot of stuff. With the added benefit of being able to go somewhere else.
PS: You also get more energy from hydrogen the further up the chain you go. A multi stage reactor that's spitting out lead provides more energy.
lead is not the endpoint of fusion, iron is.
if you expect to take a 100,000 year trip you should expect to live off the land and mine Kuiper belt objects and rouge planets. And figure that once people have lived 10,000 years under those conditions they probably won't find anything interesting about terrestrial planets.
if you expect to take a 100,000 year trip you should expect to live off the land and mine Kuiper belt objects and rouge planets. And figure that once people have lived 10,000 years under those conditions they probably won't find anything interesting about terrestrial planets.
> A hypothetical example with zero velocity would allow you to gather fuel without any drag. //
What do you mean by this, zero velocity within an atmosphere won't gather anything?
What do you mean by this, zero velocity within an atmosphere won't gather anything?
Space is not an absolute vacuum which is why this works in the first place. If your ship sits in the interstellar medium so it's not being pushed around on net then by definition it's drag is zero. However, it's possible to collect some non zero amount of hydrogen and thus energy by putting a high vacuum pump to empty space. Efficiency left as an exercise to the reader. But, it would operate the same way as a vacuum pump inside an atmosphere, just vastly slower with random particle motion providing a continuous stream of new particles.
Rest of the idea:
The Ramjet works by collecting hydrogen and Helium from a large area because you have a high relative velocity to the medium which also imposes drag. Think filter feeding whales. So you are collecting linearly more matter and thus energy per unit time with increased speed. However, drag is a function of matter collected AND relative speed so something like velocity ^3.
This suggests there is some point where you get less energy from collecting that you lose in drag. But, this also means below some speed you get more.
Rest of the idea:
The Ramjet works by collecting hydrogen and Helium from a large area because you have a high relative velocity to the medium which also imposes drag. Think filter feeding whales. So you are collecting linearly more matter and thus energy per unit time with increased speed. However, drag is a function of matter collected AND relative speed so something like velocity ^3.
This suggests there is some point where you get less energy from collecting that you lose in drag. But, this also means below some speed you get more.
> The missions targeted by this technology are GOCE-like spacecrafts which by design must fly low
Once the technology matures, it could be used by more missions. Flying low has its benefits:
* Lower latency for communication satellites,
* Better resolution for Earth imaging / spy satellites,
* When the satellite fails, it quickly deorbits by itself.
Until now, flying low has just not been economical, but if this thruster has similar lifetime to medium and high orbit satellites, then many more missions could choose lower orbits.
Once the technology matures, it could be used by more missions. Flying low has its benefits:
* Lower latency for communication satellites,
* Better resolution for Earth imaging / spy satellites,
* When the satellite fails, it quickly deorbits by itself.
Until now, flying low has just not been economical, but if this thruster has similar lifetime to medium and high orbit satellites, then many more missions could choose lower orbits.
>When the satellite fails, it quickly deorbits by itself.
This also means that failure recovery will be quite tricky if possible at all. There are some downsides to other points too: such a satellite would work at very thin margins due to the thruster being inefficient with air as a propellant. Its ground swath width will be lower, coverage will be worse, requiring more ground stations (remote sensing is very often limited by the downlink bandwidth). Also, some kind of aerodynamic shape will be required, limiting its capabilities and power budget. (electric propulsion needs a lot of power itself)
This also means that failure recovery will be quite tricky if possible at all. There are some downsides to other points too: such a satellite would work at very thin margins due to the thruster being inefficient with air as a propellant. Its ground swath width will be lower, coverage will be worse, requiring more ground stations (remote sensing is very often limited by the downlink bandwidth). Also, some kind of aerodynamic shape will be required, limiting its capabilities and power budget. (electric propulsion needs a lot of power itself)
"Quickly" in this context is probably still weeks, and you could carry a little backup system to kick it into higher orbit in case of trouble. But really, low-flying com or imaging sats are probably parts of large, "cheap" constellations and meant to be of limited lifespan.
>This also means that failure recovery will be quite tricky if possible at all
Nowadays it's probably cheaper to send a new one than doing a whole Hubble like hot fix with a space shuttle
Nowadays it's probably cheaper to send a new one than doing a whole Hubble like hot fix with a space shuttle
I'm not talking about on-orbit servicing though. Failure recovery is done all the time with most satellites. The operator just needs some time to determine the nature of the problem, possibly doing some workaround. With a low flying satellite you don't have much time for that.
failure recovery in the context of spacecraft usually means software-commands sent via TT&C (tracking, telemetry and control) channel to switch to another piece of hardware, part of the N+1 or 1+1 configuration on the spacecraft. It is incredibly exceptionally rare for a human to ever visit a satellite once in orbit.
They did it a few times in the 1980s with the shuttle, including recovery of a satellite to prove it could be done, and there were the hubble servicing missions. But other than that no human has ever touched a satellite once it's in orbit.
They did it a few times in the 1980s with the shuttle, including recovery of a satellite to prove it could be done, and there were the hubble servicing missions. But other than that no human has ever touched a satellite once it's in orbit.
This does not preclude the possibility of spacecraft doing repeated dips only on the perigee
True, interesting idea.
[Long edit]
Thinking further about this idea, I realize this may even mitigate the catch 22 problem of very low orbits (<180km): the lower the orbit, the larger the drag and the required thrust power, meaning the solar arrays must be bigger, which in turn further increases the drag... Calculations suggests that with current solar array and thruster technology, flying lower than 150km with this concept is impossible.
But with an elliptic orbit, energy from the solar arrays can be stored on the low-drag portion of the orbit too and used during the perigee dip, thus decreasing the requirements in terms of solar arrays area.
[Long edit]
Thinking further about this idea, I realize this may even mitigate the catch 22 problem of very low orbits (<180km): the lower the orbit, the larger the drag and the required thrust power, meaning the solar arrays must be bigger, which in turn further increases the drag... Calculations suggests that with current solar array and thruster technology, flying lower than 150km with this concept is impossible.
But with an elliptic orbit, energy from the solar arrays can be stored on the low-drag portion of the orbit too and used during the perigee dip, thus decreasing the requirements in terms of solar arrays area.
I'm now imagining a craft that folds up its solar panels before dipping into the atmosphere to gather fuel / accelerate. I'm sure I've built that in KSP, :p.
That is not particulary far-fetched either: the ISS already reorients its solar panels when not illuminated by the sun. They call it the "night glider mode" [1].
[1] https://en.wikipedia.org/wiki/Night_Glider_mode
[1] https://en.wikipedia.org/wiki/Night_Glider_mode
Night Glider sounds vaguely like some 80s TV show. I do hope everyone on board is required to wear non-functional sunglasses during night glide.
> The implementation of drag-reducing flight modes of the space station resulted in saving about 1,000 kg of orbital-maintenance propellant per year.
Here's an example where the authors propose doing this for planetary gravity assists, e.g., instead of using Venus for a normal gravity assist, dig into its atmosphere. Everything would need to be folded up first.
"Hypersonic Interplanetary Flight: Aero Gravity Assist"
Al Bowers & Dan Banks, 2006
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/200900...
Discussed in a podcast here: https://theorbitalmechanics.com/show-notes/al-bowers
"Hypersonic Interplanetary Flight: Aero Gravity Assist"
Al Bowers & Dan Banks, 2006
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/200900...
Discussed in a podcast here: https://theorbitalmechanics.com/show-notes/al-bowers
This would have the added benefit of increased efficiency due to the Oberth effect; however, I'm still not sure you could use it for unassisted interplanetary flight. The last orbit, by definition, must occur before the craft passes Earth escape velocity -- the question is, in that last pass through perigee, can you get enough delta V to make it to another planet? Otherwise, you'd need supplemental propellant. It's still useful, it's just not something I would describe as "revolutionary" for interplanetary travel.
Since the TWR of electric thrusters tends to be pretty abysmal, my gut is that you probably couldn't scale up the thruster well enough to bounce between planets without that supplemental propellant.
That being said, as others have mentioned, this would be really quite interesting for stationkeeping at low orbital altitudes, particularly for small satellites.
Since the TWR of electric thrusters tends to be pretty abysmal, my gut is that you probably couldn't scale up the thruster well enough to bounce between planets without that supplemental propellant.
That being said, as others have mentioned, this would be really quite interesting for stationkeeping at low orbital altitudes, particularly for small satellites.
ISS is at 150km and needs costly refueling, right? Wouldn’t that be the most interesting applicaton in terms of cost savings?
ISS is at 400+ km altitude where the atmosphere is really thin. It's also very heavy for low thrust electric propulsion.
Electric thrusters have a low thrust to weight ratio but there's nothing stopping you, in theory, from just scaling up. The ISS only experiences a little drag so an electric drive trying to zero that out doesn't need a huge thrust. There's some interest in adapting VASIMR for ISS station keeping. It would work, in theory, to just put a large number of Hall effect thrusters on the back but the piping would be infeasible.
It also needs resupply missions for food, air, and crew anyway. Reboost is almost a footnote.
> Assuming it could collect more than it needs to keep itself in orbit, it could refuel a tank
That's not this device though, it looks like the "collected" air runs straight into the thruster, like the flow through a jet engine. No tank involved.
That's not this device though, it looks like the "collected" air runs straight into the thruster, like the flow through a jet engine. No tank involved.
That's a cool thought. You could perhaps use the atmosphere of planets to accelerate at very high velocities with the energy stored between each body (which would be a lot .. ie 60 days of 24/7 solar harvesting).
The question is whether the thrust you produce is roughly linear with the energy you expel? Or does it taper asymptotic? What if the power system on the craft is titanium batteries that are designed to deliver 1 MW for say 2 minutes? Will that give you the needed acceleration in a given planets atmosphere? What if you use planetary lasers and don't need batteries at all?
The question is whether the thrust you produce is roughly linear with the energy you expel? Or does it taper asymptotic? What if the power system on the craft is titanium batteries that are designed to deliver 1 MW for say 2 minutes? Will that give you the needed acceleration in a given planets atmosphere? What if you use planetary lasers and don't need batteries at all?
Solar light isn't that strong once you go beyond mars.
Earth gets 1400 W/m^2, at Saturn only 16 W/m^2 and on Neptune maybe 1.5 W if you get lucky.
60 days of continous harvesting, assuming the spacecraft doesn't use any power (which is not true in reality), is about 2 kWh at Neptune. Not that much. Saturn would be 23 kWh.
Earth gets 1400 W/m^2, at Saturn only 16 W/m^2 and on Neptune maybe 1.5 W if you get lucky.
60 days of continous harvesting, assuming the spacecraft doesn't use any power (which is not true in reality), is about 2 kWh at Neptune. Not that much. Saturn would be 23 kWh.
Yuck, that’s miserable.
It's the inverse square law that bites you here as the same amount of energy gets stretched out into a larger sphere as it travels outwards (at earth the energy is 1.4kW for a square meter, when going outwards, this square meter gets stretched)
Double the distance and you get 1/4th the energy.
Saturn is 9AU or 9 times as far as earth; 1/81th the energy. (1400 / 9^2 = 17, so math checks out; roughly)
We're quite lucky to be close enough for solar energy to be a viable source of energy.
[*]: https://en.wikipedia.org/wiki/Inverse-square_law
Double the distance and you get 1/4th the energy.
Saturn is 9AU or 9 times as far as earth; 1/81th the energy. (1400 / 9^2 = 17, so math checks out; roughly)
We're quite lucky to be close enough for solar energy to be a viable source of energy.
[*]: https://en.wikipedia.org/wiki/Inverse-square_law
> We're quite lucky to be close enough for solar energy to be a viable source of energy.
If solar energy were not viable, this form would not exist.
If solar energy were not viable, this form would not exist.
If solar energy were not viable, Hacker News posts might be written by technologically inclined chemoautotrophs hacking in the basement of their hydrothermal vent.
https://en.wikipedia.org/wiki/Chemosynthesis
Just because solar cells don't work doesn't mean photosynthesis wouldn't work.
It may not work on any planet. A fundamental design challenge is that increased size of solar panels create more drag, and increasing the height to reduce drag means it must go faster which further increases drag. While the Solar Impulse has demonstrated an equilibrium of speed-to-size can be maintained at normal altitude and low speed, we'll have to wait to see if something can be built to sustain equilibrium at these heights.
"Sorry data, air may be the eventual oil."
Trivia question: How many round-trips from Neptune would it take to cause a 1% dip in Earth's air content?
Bonus question: Since the Earth is not making any more Xenon, are we losing some of this resource to the deep space every time we nudge a satellite?
Trivia question: How many round-trips from Neptune would it take to cause a 1% dip in Earth's air content?
Bonus question: Since the Earth is not making any more Xenon, are we losing some of this resource to the deep space every time we nudge a satellite?
A lot; also keep in mind that air is not a finite resource, it's continually generated from e.g. electrolysis (h2o -> o) and other processes (carbon + oxide = c02, plenty of carbon on earth, plenty of oxygen). Plus as another commenter mentioned, we're already losing some air all the time anyway.
Tangentially related question - what happens to the gas used as a reaction mass in thrusters in orbit - when it's used to speed up I guess it falls down cause velocities mostly cancel out, but when it's used to slow down the ship, and engines are fired retrograde - the reaction mass has orbital velocity, right?
Does it stay in some orbit forever, like a solid object would? Can it cause gas "Kessler syndrome", with gas rings around Earth's most common reaction mass orbits?
If we choose our orbits and burn times so that this gas piles up in particular place on particular orbit, can we then reuse that as "air" for these engines from the article?
Does it stay in some orbit forever, like a solid object would? Can it cause gas "Kessler syndrome", with gas rings around Earth's most common reaction mass orbits?
If we choose our orbits and burn times so that this gas piles up in particular place on particular orbit, can we then reuse that as "air" for these engines from the article?
The exhaust velocity in a xenon ion thruster is 20-50 km/s. Most of the time it’s on an earth escape trajectory (~11 km/s in low orbit).
The smaller an object is the less time it takes for drag from the super tenuous atmosphere up in orbit to slow it down so it falls back to Earth. Gas molecules are very low mass and I expect that the exhaust for any given thruster will be gone quickly, even in the higher levels of LEO.
Xenon's very heavy, most of it would eventually come back down to Earth - probably sooner rather than later. Most of what we lose to deep space is hydrogen and helium. And almost none of that is from space missions, anyway, it's just Brownian motion.
Isn't it a matter of speed rather than mass? If the xenon is ejected faster than the escape velocity, it seems like it would get off Earth's gravity.
In fact I think it would have to be roughly twice the escape velocity since the spacecraft is already going near it in one direction. According to Wikipedia[1] the exhaust velocity of an ion thruster is between 20 to 50 km/s when the Earth escape velocity is 11km/s [2]
[1]: https://en.wikipedia.org/wiki/Ion_thruster [2]: https://en.wikipedia.org/wiki/Escape_velocity
so I would assume most of it is lost in space
In fact I think it would have to be roughly twice the escape velocity since the spacecraft is already going near it in one direction. According to Wikipedia[1] the exhaust velocity of an ion thruster is between 20 to 50 km/s when the Earth escape velocity is 11km/s [2]
[1]: https://en.wikipedia.org/wiki/Ion_thruster [2]: https://en.wikipedia.org/wiki/Escape_velocity
so I would assume most of it is lost in space
Velocity alone doesn't answer the question. Direction matters.
My assumption (knowing nothing but basic Physics), is that the xenon is ejected in a direction slightly toward the earth, and mostly directly in the opposite direction of the current travel, because that's what would be necessary to counteract drag and keep a satellite on the same path.
This means that if the satellite is going almost 11km/s one direction, the xenon will have that much less speed compared to the earth. And the trajectory will be slightly toward the earth.
I would assume that makes it substantially more likely that the xenon falls back to earth.
My assumption (knowing nothing but basic Physics), is that the xenon is ejected in a direction slightly toward the earth, and mostly directly in the opposite direction of the current travel, because that's what would be necessary to counteract drag and keep a satellite on the same path.
This means that if the satellite is going almost 11km/s one direction, the xenon will have that much less speed compared to the earth. And the trajectory will be slightly toward the earth.
I would assume that makes it substantially more likely that the xenon falls back to earth.
It depends on whether the propellant is used to increase or decrease the orbital velocity of the vessel.
Acceleration propellant would have to be ejected at the orbital velocity of the vessel plus escape velocity to escape. Deceleration propellant would just have to be ejected at escape velocity minus orbital velocity.
As deceleration near atmosphere is almost free just by dipping into it, or by using some form of sea anchor to pull on the atmosphere or magnetic field, it is more likely that propellant would be used preferentially for attitude control and acceleration.
It isn't impossible, but imparting enough velocity to propellant for it to escape Earth orbit--while accelerating a vessel in the opposite direction--seems unlikely for orbital station-keeping. You need at least 12000 m/s for escape velocity plus at least 8000 m/s to counteract the orbit you were already in, so the propellant would have to leave the vessel at more than 20000 m/s. That's a specific impulse of about 2000 s. Ion drives and VASIMR could do it, but the propellant is very likely to experience its own atmospheric drag and electromagnetic interactions, and the probability that any particular atom of propellant would actually escape with the minimum velocity-relative-to-vessel is very low. The propellant would spread out to a larger volume as quickly as it could, too. It's far more likely that one of those xenon ions would collide with a hydrogen atom in the upper atmosphere and randomly bounce it out, like a bowling ball hitting a billiard ball.
Acceleration propellant would have to be ejected at the orbital velocity of the vessel plus escape velocity to escape. Deceleration propellant would just have to be ejected at escape velocity minus orbital velocity.
As deceleration near atmosphere is almost free just by dipping into it, or by using some form of sea anchor to pull on the atmosphere or magnetic field, it is more likely that propellant would be used preferentially for attitude control and acceleration.
It isn't impossible, but imparting enough velocity to propellant for it to escape Earth orbit--while accelerating a vessel in the opposite direction--seems unlikely for orbital station-keeping. You need at least 12000 m/s for escape velocity plus at least 8000 m/s to counteract the orbit you were already in, so the propellant would have to leave the vessel at more than 20000 m/s. That's a specific impulse of about 2000 s. Ion drives and VASIMR could do it, but the propellant is very likely to experience its own atmospheric drag and electromagnetic interactions, and the probability that any particular atom of propellant would actually escape with the minimum velocity-relative-to-vessel is very low. The propellant would spread out to a larger volume as quickly as it could, too. It's far more likely that one of those xenon ions would collide with a hydrogen atom in the upper atmosphere and randomly bounce it out, like a bowling ball hitting a billiard ball.
Generally, electric propulsion is used for two purposes in Earth-orbiting spacecraft: for correcting the orbit (station-keeping) and for raising the orbit from an intermediate to the target one (in relatively recent all-electric GEO sats)
Station-keeping requires relatively short burns (sub-hour to several hours) in all directions. When raising the orbit, the spacecraft usually keeps itself in fixed position relative to the Sun to maximize the solar panel output. The propulsion unit keeps working at all times, both in prograde and retrograde, because efficient Hall thrusters are tricky to work with in impulse mode, and are heavily optimized for continuous operation.
So in most cases, xenon is ejected in arbitrary directions, retrograde being only one of them. Besides, some ion/plasma thrusters are so efficient that they eject the propellant at more than double escape velocity. I would guess most of the propellant actually leaves the gravity well; also, at higher altitudes where electric propulsion is mostly used there's no atmosphere to collide with.
Station-keeping requires relatively short burns (sub-hour to several hours) in all directions. When raising the orbit, the spacecraft usually keeps itself in fixed position relative to the Sun to maximize the solar panel output. The propulsion unit keeps working at all times, both in prograde and retrograde, because efficient Hall thrusters are tricky to work with in impulse mode, and are heavily optimized for continuous operation.
So in most cases, xenon is ejected in arbitrary directions, retrograde being only one of them. Besides, some ion/plasma thrusters are so efficient that they eject the propellant at more than double escape velocity. I would guess most of the propellant actually leaves the gravity well; also, at higher altitudes where electric propulsion is mostly used there's no atmosphere to collide with.
Wow, you're right, I vastly underestimated the exhaust velocity.
You'd still have to account for its interaction with the atmosphere, but my point is moot.
You'd still have to account for its interaction with the atmosphere, but my point is moot.
It's not Xenon you have to worry about, it's Helium. Once we run out we'll be too heavy and fall into the sun.
It is not mentioned in detail in the article, but it's worth looking up what the GOCE satellite was. Unlike 99.9% of satellites ever built, it was designed to be shaped sort of like a rectangular missile with solar panel wings. The idea was to make it slightly more aerodynamic and thus prolong its lifespan at very low orbit altitude, with ion thruster and tank of propellant.
So, possibly dumb question: is this basically a fan without moving parts?
This is a prototype so I'm guessing the size/cost can be reduced in the future, and if it becomes small/cheap, I could see a fan without moving parts having a lot of applications.
This is a prototype so I'm guessing the size/cost can be reduced in the future, and if it becomes small/cheap, I could see a fan without moving parts having a lot of applications.
Absolutely, this is a passive compressor.
It kind of works like an aerodynamic diode: it is much easier for the incoming particles to go through the intake tubes (because they are oriented along the spacecraft velocity vector) than to exit the collector. This is because after a they collide with surfaces inside the collector, their velocity vector is randomized and no longer aligned with the tubes.
[Edit] Mass is not such an issue when you contrast it with the mass of propellant that you save...
[Edit2] I forgot to precise that my description only pertained to the intake part: there is of course a plasma thruster at the back (no moving part either)
It kind of works like an aerodynamic diode: it is much easier for the incoming particles to go through the intake tubes (because they are oriented along the spacecraft velocity vector) than to exit the collector. This is because after a they collide with surfaces inside the collector, their velocity vector is randomized and no longer aligned with the tubes.
[Edit] Mass is not such an issue when you contrast it with the mass of propellant that you save...
[Edit2] I forgot to precise that my description only pertained to the intake part: there is of course a plasma thruster at the back (no moving part either)
Is the principle behind the Feynman sprinkler involved in any way?
[0] https://en.wikipedia.org/wiki/Feynman_sprinkler
[0] https://en.wikipedia.org/wiki/Feynman_sprinkler
No
[deleted]
It works by ionizing the air, so that might lead to issues with producing ozone.
Ozone in the high atmosphere is a good thing though - the ozone layer. It's only at ground level that it can act as a health hazard.
Yeah, I should have clarified: I was responding to the "having a lot of applications" remark, which to me implied other places than low earth orbit.
Definitely. Ozone is a significant irritant (although it also has an "air freshening effect", see air ionizers), to produce significant airflow I believe you'd need very large electrodes, which would produce lots of ozone. The electrodes need to be large because the voltage is limited by air's breakdown voltage, so you can't just pump up the voltage like you can (for the most part) just increase a fan's velocity.
For lack of friction/bearings a magnetic bearing fan seems like a much better option. The strength of this technology is the great exhaust velocity, which is great for space applications.
For lack of friction/bearings a magnetic bearing fan seems like a much better option. The strength of this technology is the great exhaust velocity, which is great for space applications.
> The strength of this technology is the great exhaust velocity, which is great for space applications.
Ah, that makes sense. Given the speed that these satellites are typically travelling at, the exhaust probably needs to go faster than that to work, right?
Ah, that makes sense. Given the speed that these satellites are typically travelling at, the exhaust probably needs to go faster than that to work, right?
...not at the quantities this thing would make.
I'd be more worried about random Nitrogen Oxides (NOx) emissions, but again, too small of a volume to actually matter in any significant way. A couple of VWs are probably worse.
I'd be more worried about random Nitrogen Oxides (NOx) emissions, but again, too small of a volume to actually matter in any significant way. A couple of VWs are probably worse.
Fair point. Although you don't run VWs in closed spaces, but one might do so with fans (same reason why I hate it when universities or offices put laserprinters in closed rooms - always gives me headaches)
it ionizes the incoming gas and then accelerates it to very high speed with an electric field. My guess is that wouldn’t work well in normal atmospheric conditions but no idea really.
The gas collecting portion of this design wouldn't work well, but it's certainly possible to generate thrust by ionizing air at atmospheric pressure and zero relative velocity. See https://en.wikipedia.org/wiki/Ionocraft#Mechanism and https://www.youtube.com/watch?v=vzZy1Aqleno
The main challenge is whether the ionization creates enough thrust to overcome drag; this seems to be true in the upper atmosphere, but not sure if that works in the lower. Then again, you could probably do it, but it'd require more energy.
there already are fans without moving parts, manufactured by Dyson.
Edit: wrong... see below. Thx, walrus!
Edit: wrong... see below. Thx, walrus!
They have moving parts. There's a normal fan at the bottom. See here:
https://en.wikipedia.org/wiki/Bladeless_fan
https://en.wikipedia.org/wiki/Bladeless_fan
There is an ordinary fan in the base and the ring is hollow with slots in it.
If you're not limited by propellant, it seems like this would be really useful for satellites that need to change orbit frequently. Performing a plane change, for example, normally requires a prohibitive amount of propellant, but if that is essentially free, you can change orbit at will, albeit somewhat slowly.
Is no-one going to comment on how beautifully sci-fi that engine looks when running?
Wonder if this would work nicely with a highly elliptical orbit like Molniya. When it gets closer to the atmosphere it scoops up some more gas, then when it is further away it provides nice wide coverage.
At first I thought that this was a type of magnetohydrodynamic drive[1]. I've have watched a video of one of the french scientists who has been studying electric propulsion systems. Sadly the video quickly went downhill into pure conspiracy theory realm.
[1]: https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive
[1]: https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive
It's a giant ionic breeze!
There are less accurate ways to explain it.
It’s an elephant!
I just finished reading the second of the Ringworld books, and this seems very much like a first step towards the ramjets the book is all about.
so, to-do:
* find way to scoop up more incoming material
* replace electric propulsion with sth more powerful
* write smug think piece about how sci-fi guides engineering
so, to-do:
* find way to scoop up more incoming material
* replace electric propulsion with sth more powerful
* write smug think piece about how sci-fi guides engineering
Ringworld posited interstellar Bussard ramjets [1]. Since they were proposed (and Ringworld written) we have discovered there isn’t enough hydrogen in interstellar space to make such vehicles feasible.
[1] https://en.m.wikipedia.org/wiki/Bussard_ramjet
[1] https://en.m.wikipedia.org/wiki/Bussard_ramjet
I haven't read Ringworld, but are you sure that it is not describing this already existing technology?
https://en.wikipedia.org/wiki/Ramjet
https://en.wikipedia.org/wiki/Ramjet
This might be needed if we succumb to the Kessler Syndrome. By operating in the upper atmosphere, we could continue to have satellites while there's a maelstrom of high-hypersonic bullets overhead.
Interesting - was just reading this morning about Astranis & their low-orbit satellites to supply more of the world with broadband
Seems like a tie-in, although Electric Thrusters themselves look bigger than the satellites right now.
That's everything I know about both subjects, so no idea if this is a useful comment or not :-)
Seems like a tie-in, although Electric Thrusters themselves look bigger than the satellites right now.
That's everything I know about both subjects, so no idea if this is a useful comment or not :-)
Astranis is launching satellites to GEO [1], i.e., not low.
[1] https://techcrunch.com/2018/03/01/astranis-emerges-from-stea...
[1] https://techcrunch.com/2018/03/01/astranis-emerges-from-stea...
You're right. The article I read was more business oriented and used both terms, and I didn't notice.
kind of offtopic, I was reading yesterday about this new Hall thruster from NASA [0]. Amazing achievment!
[0] https://news.engin.umich.edu/2017/10/thruster-for-mars-missi...
[0] https://news.engin.umich.edu/2017/10/thruster-for-mars-missi...
This is just an application of the Biefeld-Brown effect (also seen in ionocraft and "lifters"). Nice to finally see it in use in satellites, though.
https://en.wikipedia.org/wiki/Biefeld%E2%80%93Brown_effect
First thought was, what other industries and applications could this potentially serve?
[deleted]
Except it's not the first:
http://www.busek.com/technologies__hall.htm
Yes, operating a Hall or ion thruster on O2 and/or N2 is not new (and Busek was not the only one that did it either).
And it is definitely hard, but this is just part of the problem.
The really tricky thing is to get the whole system working. For instance it is not longer possible to use a "high pressure" (relatively speaking of course) propellant feed. Even with the passive compression stage discussed in the article, an off-the-shelf thruster wouldn't be able to operate due to the low inlet pressure.
Also, the intake/collector design is a problem of its own. AFAIK this was the first real-life test for the passive intake concept (the theory of operation and trade-off to be considered are discussed here [1]).
That being said there is still a long way to go before this can work in space...
[1] http://erps.spacegrant.org/uploads/images/2015Presentations/...
And it is definitely hard, but this is just part of the problem.
The really tricky thing is to get the whole system working. For instance it is not longer possible to use a "high pressure" (relatively speaking of course) propellant feed. Even with the passive compression stage discussed in the article, an off-the-shelf thruster wouldn't be able to operate due to the low inlet pressure.
Also, the intake/collector design is a problem of its own. AFAIK this was the first real-life test for the passive intake concept (the theory of operation and trade-off to be considered are discussed here [1]).
That being said there is still a long way to go before this can work in space...
[1] http://erps.spacegrant.org/uploads/images/2015Presentations/...
The page doesn't go into any detail, but it looks like this would require the air to come from a tank? Otherwise surely they would have mentioned it, not requiring on-board propellant is the feature of this thruster.
How much thrust does this produce?
forgive my ignorance, but....could this be applied to aircraft? Make a near fuel-less jet?
The air this thruster gathers isn't used as fuel, only as propellant. The energy needed to accelerate the propellant and generate thrust still has to come from somewhere.
Aircraft don't need propellant; they can simply "push off" of the air (via propellers, turbofan engines, etc); so this mechanism is useless for them. They still need fuel to run their engines, which this device doesn't provide.
Aircraft don't need propellant; they can simply "push off" of the air (via propellers, turbofan engines, etc); so this mechanism is useless for them. They still need fuel to run their engines, which this device doesn't provide.
Ion engines have very low thrust, so they're not suitable for in-atmosphere work. In space they can apply a gentle thrust for a long time, which is useful.
Ion engines also only typically ignite in a near vacuum as well. You would need HUGE voltages to do the same thing in the (main part of the) atmosphere.
Spelling error in title. Should be ... Electric Thruster
I thrust it will be fixed.
Whoops! Yes, I fixed it. Thanks for noticing. :-)
And here I spend a good minute staring at the title, looking for the (now gone) spelling error.
I had to reread this headline a few times, believing "Electric Truster" to be the esoteric job title of someone recently fired.
[deleted]
So, just to be clear (because I don't see it mentioned anywhere). Are we taking about the EMDrive here?
No. This is a ion thruster, a class of thrusters which already exist and are used in various satellites. They carry a propellant (xenon), then use electricity to accelerate and shoot the propellant out the back. This provides extremely efficient, but low amount of thrust (like a nudge).
This development gets rid of the need to carry propellant. They satellite will scoop it up from the atmosphere, saving weight and prolonging life.
This development gets rid of the need to carry propellant. They satellite will scoop it up from the atmosphere, saving weight and prolonging life.
So "air collecting" or "mass collecting" would be more accurate since it doesn't really breath like a typical air breathing engine?
It doesn't accelerate the air like a typical air breathing engine, but it certainly ingests the air like one. It's basically a ramjet but uses electric charge to accelerate the exhaust gas rather than hydrocarbons.
This is a customized Hall thruster.
Disclosure: I was involved in that project.
Disclosure: I was involved in that project.
Do you know, is related to this study? [0]
[0] http://erps.spacegrant.org/uploads/images/images/iepc_articl...
[0] http://erps.spacegrant.org/uploads/images/images/iepc_articl...
Yes, this is related (not the author of the cited article but I know him well).
There were also several precursor experimental studies funded by ESA, one of which [1] can be found in the same conf. proceeding.
[1] http://erps.spacegrant.org/uploads/images/images/iepc_articl...
There were also several precursor experimental studies funded by ESA, one of which [1] can be found in the same conf. proceeding.
[1] http://erps.spacegrant.org/uploads/images/images/iepc_articl...
They just throw stuff out the back of the rocket really fast to move forward, like any other sort of rocket. The nice thing about electrical rockets is that they decouple the energy used to throw the propellant from the chemical energy generated from burning the fuel, so you can end up throwing it out fast for very efficient rockets if you have enough electricity.
http://hopefullyintersting.blogspot.com/2015/03/rockets-elec...
http://hopefullyintersting.blogspot.com/2015/03/rockets-elec...
ELY 5:
No, this is actual Newtonian physics. Rockets function based on Newton's third law: every reaction creates an equal and opposite reaction. We sit on wheeled office chairs, I push you- we both move, to opposite directions.
Rockets aren't fueled by office chairs, though, but by gases. They push the gas molecules into a particular direction and themselves are pushed into another.
So, to move in space by pushing stuff, you need two things: a) mass to push away b) some power to do the pushing
(This ignores several categories of other forms of force generation on space craft like solar sails).
Chemical fuel rockets happen to strike two flys on one go - the mass they carry also generate the energy for the push, so that's only a matter of plumbing and hydrodynamics to get them going.
The problem with this approach, though, is that once you run out of fuel, you run out of fuel. No more chairs, no more acceleration. Refueling in space is really expensive, if you need to bring up the propellant from a deep gravity well like earths surface to the orbit (https://xkcd.com/681/).
There is no necessity the propellant (i.e the 'chairs') needs to generate the energy for pushing itself away. You can you Some Other Physics to push the propellant away from the vehicle. It works just as fine.
This system collects the fuel from sparse gas surrounding it, and expels it using an electric thruster, which probably get's it's energy from solar panels.
Potentially, like some other poster noted, you could design a spacecraft with this that once it reaches planetary orbit, it can hop from planet to planet and refuel itself indefinetly (just as long as the planets have an atmosphere).
So it's Way Cool, and this has been hypothesized in science fiction for decades, so it's also Genuine Scifi Space Tech :)
No, this is actual Newtonian physics. Rockets function based on Newton's third law: every reaction creates an equal and opposite reaction. We sit on wheeled office chairs, I push you- we both move, to opposite directions.
Rockets aren't fueled by office chairs, though, but by gases. They push the gas molecules into a particular direction and themselves are pushed into another.
So, to move in space by pushing stuff, you need two things: a) mass to push away b) some power to do the pushing
(This ignores several categories of other forms of force generation on space craft like solar sails).
Chemical fuel rockets happen to strike two flys on one go - the mass they carry also generate the energy for the push, so that's only a matter of plumbing and hydrodynamics to get them going.
The problem with this approach, though, is that once you run out of fuel, you run out of fuel. No more chairs, no more acceleration. Refueling in space is really expensive, if you need to bring up the propellant from a deep gravity well like earths surface to the orbit (https://xkcd.com/681/).
There is no necessity the propellant (i.e the 'chairs') needs to generate the energy for pushing itself away. You can you Some Other Physics to push the propellant away from the vehicle. It works just as fine.
This system collects the fuel from sparse gas surrounding it, and expels it using an electric thruster, which probably get's it's energy from solar panels.
Potentially, like some other poster noted, you could design a spacecraft with this that once it reaches planetary orbit, it can hop from planet to planet and refuel itself indefinetly (just as long as the planets have an atmosphere).
So it's Way Cool, and this has been hypothesized in science fiction for decades, so it's also Genuine Scifi Space Tech :)
Doesn't look like it. This type of drive has been around, but the issue had been that it would run out of propellant that powered it to keep the satellite in low earth orbit. This is the successful testing of a drive of the same type, but it collects that material from the atmosphere so it hopefully it won't run out for a long time and keep missions running longer.
From a cursory reading, it doesn't sound anything like that at all.
https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster
https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster
[deleted]
Don't think so. Sounds like it accelerates air particles using electricity.
[deleted]
Still, atmospheric fuel scoops were still sci-fi until now, as far as I’m aware.