ESA fires an air-breathing electric thruster for low orbits

[YNM]

2 hours ago, Northstar1989 said:

But I'm not surprised nobody there brought up Propulsive Fluid Accumulators.

Well yeah... sorry for thinking this was just another news announcement.

I do wonder about the efficiency of such setup though. You'd basically catch air but you need to poot some in the back to keep moving.

Also, the "molecules" up there are a bit... different.

[Nefrums]

2 hours ago, Rakaydos said:

Is the atmospere at 200 km the same proportions as lower, or is there gravity-separation?

If it's the same, you're collecting 78% nitrogen and 21% oxygen. The oxygen is useful, but the nitrogen tkes a lot of processing to become usful nitrogen compounds, and can probably be tossed. The question is whether your PFA can split different types of gasses in orbit, or whether it justcompresses them and lets another vessel handle separation.

the proportions is different:

"The lighter constituents atomic oxygen (O), helium (He), and hydrogen (H) successively dominate above about 200 km altitude"

https://en.wikipedia.org/wiki/Thermosphere

 

[PB666]

On 3/7/2018 at 7:12 AM, Gaarst said:

I just found out about this (article is a couple days old) and it seems nobody made a thread about it here yet, so here we are:

http://www.esa.int/Our_Activities/Space_Engineering_Technology/World-first_firing_of_air-breathing_electric_thruster

From what I understand, it is basically your average ion thruster except instead of a Xe tank as propellant, it has an intake that collects the few air molecules at 200 km altitude which are then ionised and accelerated like conventional ion thrusters do xenon.

Applications are essentially for satellites orbiting in very low orbits (around 200km) for long periods, removing the need for internal fuel tanks and extending the lifetime: the article cites the GOCE satellite (Earth gravitational field mapper) which expanded 40 kg of xenon over its 4.5 years in a ~250 km circular orbit. I'm guessing most uses will be in various Earth observation/mapping missions where lower altitude means better resolution, but hopefully they will be able to improve on the concept to make it work at higher altitudes where drag becomes small enough that the thurster can be used to maneuver around (cheap LEO to GTO insertions in many passes comes to mind).

No testing mission is mentioned in the article though, so this is probably still in very early stages of development and perhaps not usable at the moment.

This is why one want to place a spacecraft on the edge of the safe "zone" at 400 km or so (that way you can wave to the ISS as you pass).

The problem is that at 250km your craft is traveling at 7700 m / second, you are scooping up particles which means, they are imparting all their momentum into your space craft. To compensate you must expel that gas at >7700

So for your typical spacecraft you have your vessel which is a boxy thing a couple meters in diameter (or less) and these big bulky solar panels (often which cross sectional areas 3 or 4 times the area of your craft.

To make this work you would need to expell gas at more than 3 to 4 times the area you collect over (since you cannot collect what bounces off your solar panels). this means the exhaust velocity needs to be at least 32000 (ISP ~ 3300) which is on the high end of commercially available ION drives.

In terms of Insertion into GTO, lol, your power would not bee the limiting step, fuel flow would be, talk about nanometers/sq.second of acceleration.
 

[Vanamonde]

Overlapping threads have been merged. 

[Northstar1989]

18 hours ago, PB666 said:

This is why one want to place a spacecraft on the edge of the safe "zone" at 400 km or so (that way you can wave to the ISS as you pass).

The problem is that at 250km your craft is traveling at 7700 m / second, you are scooping up particles which means, they are imparting all their momentum into your space craft. To compensate you must expel that gas at >7700

So for your typical spacecraft you have your vessel which is a boxy thing a couple meters in diameter (or less) and these big bulky solar panels (often which cross sectional areas 3 or 4 times the area of your craft.

To make this work you would need to expell gas at more than 3 to 4 times the area you collect over (since you cannot collect what bounces off your solar panels). this means the exhaust velocity needs to be at least 32000 (ISP ~ 3300) which is on the high end of commercially available ION drives.

In terms of Insertion into GTO, lol, your power would not bee the limiting step, fuel flow would be, talk about nanometers/sq.second of acceleration.
 

Your math is wrong.

If you are traveling at 7.7 km/s and you need to expel exhaust at 4 times that velocity to maintain orbit, then this only amounts to an exhaust velocity of (7700 * 4=30800 m/s) 30.8 km/s, which is an ISP of (30800 / 9.8066 = 3140.7 seconds) 3140.7 s, not 3300 s.

Any Gridded Ion Thruster (a type closely related to this airbreathing design) can easily beat this ISP- indeed the Dual Stage 4 Grid design can achieve exhaust velocities of 210 km/s (21,414 seconds ISP).

https://en.m.wikipedia.org/wiki/Gridded_ion_thruster

KSP isn't real life.  Real electric thrusters have much higher ISP, and much lower Thrust, than the ion thrusters in KSP.

Or maybe your figures came from the Dawn/DS1 probes, which both used the NSTAR design, which maxed out its ISP around 3100 seconds...

https://en.m.wikipedia.org/wiki/Dawn_(spacecraft)

Problem is, that's not even close to the best ISP thst can be achieved.  Even the NEXT thruster, developed as a successor to the Dawn/DS1 thrusters and using similar ion thruster technology, can achieve an ISP of 4190 seconds:

https://en.m.wikipedia.org/wiki/NEXT_(ion_thruster)

Once again, though, the ESA airbreathing thruster is a dual-stage design (one that, interestingly, thermalizes the flow before ionizing it).  Which means it's going to have higher ISP but lower Thrust than any design similar to NSTAR or NEXT...

https://m.esa.int/Our_Activities/Space_Engineering_Technology/World-first_firing_of_air-breathing_electric_thruster

 

Regards,

Northstar

Edited March 10, 2018 by Northstar1989

[Nuke]

On 3/8/2018 at 9:55 AM, StrandedonEarth said:

Hmm, yes, it’s the propellant ( or reaction mass, whichever you prefer) that’s infinite. 

"infinite"

nah its just that its gas tank is the size of the earth's atmosphere. we may have come up with a way to speed up atmosphere depletion. 

[wumpus]

On 3/10/2018 at 4:34 AM, Northstar1989 said:

Once again, though, the ESA airbreathing thruster is a dual-stage design (one that, interestingly, thermalizes the flow before ionizing it).  Which means it's going to have higher ISP but lower Thrust than any design similar to NSTAR or NEXT...

Which is the crux of the issue.  Isp of an air-breather is a non-issue, but thrust is the real problem.  For maintaining LEO, "all" you need are sufficient batteries to maintain constant operation.  For GTO (and presumably escape velocity, it isn't much more) you need to accelerate from ~7km/s to ~10km/s or ~11km/s respectively.  You also have to do so only at your Pe (because that is where the air is).  Smart-1 took about a year to go from ~10km/s to ~11km/s (GTO to LTO) so a multi-year plan is not out of order.

Any design trying to do this would have to be built to handle two different modes: circular and elliptical travels.  In circular mode, all power would have to be generated with the solar panels at roughly zero angle of attack (flat to the wind).  You would also need to charge the batteries enough to provide enough power to maintain your Pe in space.  Assuming the solar panels can supply the motors with full power (and the batteries can't supply full power for circular operations) you have 3 months to get your Ap out of the atmosphere (and preferably away from the shadow of Earth).  I can't imagine the power supply being lighter than simply bringing along ~3km/s worth of Xe (or even Ar) and avoiding the atmospheric drag while using your solar panels more efficiently.

Also note that you are going through both the inner and outer Van Allen belts with every orbit.  When Smart 1 did this they avoided the inner belts (nearly all the radiation) and all other deep space probes have gone straight to escape velocity (even though using chemicals is vastly more expensive than their onboard ions).

 

[Cheif Operations Director]

On ‎3‎/‎7‎/‎2018 at 5:12 AM, Gaarst said:

I just found out about this (article is a couple days old) and it seems nobody made a thread about it here yet, so here we are:

http://www.esa.int/Our_Activities/Space_Engineering_Technology/World-first_firing_of_air-breathing_electric_thruster

From what I understand, it is basically your average ion thruster except instead of a Xe tank as propellant, it has an intake that collects the few air molecules at 200 km altitude which are then ionised and accelerated like conventional ion thrusters do xenon.

Applications are essentially for satellites orbiting in very low orbits (around 200km) for long periods, removing the need for internal fuel tanks and extending the lifetime: the article cites the GOCE satellite (Earth gravitational field mapper) which expanded 40 kg of xenon over its 4.5 years in a ~250 km circular orbit. I'm guessing most uses will be in various Earth observation/mapping missions where lower altitude means better resolution, but hopefully they will be able to improve on the concept to make it work at higher altitudes where drag becomes small enough that the thurster can be used to maneuver around (cheap LEO to GTO insertions in many passes comes to mind).

No testing mission is mentioned in the article though, so this is probably still in very early stages of development and perhaps not usable at the moment.

That's actually an really good idea. Things could stay in orbit virtually forever.

[Northstar1989]

On 3/13/2018 at 11:50 AM, wumpus said:

Which is the crux of the issue.  Isp of an air-breather is a non-issue, but thrust is the real problem.  For maintaining LEO, "all" you need are sufficient batteries to maintain constant operation.  For GTO (and presumably escape velocity, it isn't much more) you need to accelerate from ~7km/s to ~10km/s or ~11km/s respectively.  You also have to do so only at your Pe (because that is where the air is).  Smart-1 took about a year to go from ~10km/s to ~11km/s (GTO to LTO) so a multi-year plan is not out of order.

Any design trying to do this would have to be built to handle two different modes: circular and elliptical travels.  In circular mode, all power would have to be generated with the solar panels at roughly zero angle of attack (flat to the wind).  You would also need to charge the batteries enough to provide enough power to maintain your Pe in space.  Assuming the solar panels can supply the motors with full power (and the batteries can't supply full power for circular operations) you have 3 months to get your Ap out of the atmosphere (and preferably away from the shadow of Earth).  I can't imagine the power supply being lighter than simply bringing along ~3km/s worth of Xe (or even Ar) and avoiding the atmospheric drag while using your solar panels more efficiently.

Also note that you are going through both the inner and outer Van Allen belts with every orbit.  When Smart 1 did this they avoided the inner belts (nearly all the radiation) and all other deep space probes have gone straight to escape velocity (even though using chemicals is vastly more expensive than their onboard ions).

 

Nobody said anything about using this engine to boost a satellite from LEO to GTO.  Doing so would just be silly.  But if you used these engines to maintain a Propulsive Fluid Accumulator, and transferred collected gasses to a depot in a higher orbit (say 600 or 700 km) you could refuel chemical upper stages with fresh Liquid Oxygen (or Liquid Nitrogen for Thermal Rockets) at 600-700 km before sending them to GTO, the Moon, Mars or wherever...

Edited March 26, 2018 by Northstar1989

[PB666]

On 3/10/2018 at 3:34 AM, Northstar1989 said:

Your math is wrong.

If you are traveling at 7.7 km/s and you need to expel exhaust at 4 times that velocity to maintain orbit, then this only amounts to an exhaust velocity of (7700 * 4=30800 m/s) 30.8 km/s, which is an ISP of (30800 / 9.8066 = 3140.7 seconds) 3140.7 s, not 3300 s.

Any Gridded Ion Thruster (a type closely related to this airbreathing design) can easily beat this ISP- indeed the Dual Stage 4 Grid design can achieve exhaust velocities of 210 km/s (21,414 seconds ISP).

https://en.m.wikipedia.org/wiki/Gridded_ion_thruster

KSP isn't real life.  Real electric thrusters have much higher ISP, and much lower Thrust, than the ion thrusters in KSP.

Or maybe your figures came from the Dawn/DS1 probes, which both used the NSTAR design, which maxed out its ISP around 3100 seconds...

https://en.m.wikipedia.org/wiki/Dawn_(spacecraft)

Problem is, that's not even close to the best ISP thst can be achieved.  Even the NEXT thruster, developed as a successor to the Dawn/DS1 thrusters and using similar ion thruster technology, can achieve an ISP of 4190 seconds:

https://en.m.wikipedia.org/wiki/NEXT_(ion_thruster)

Once again, though, the ESA airbreathing thruster is a dual-stage design (one that, interestingly, thermalizes the flow before ionizing it).  Which means it's going to have higher ISP but lower Thrust than any design similar to NSTAR or NEXT...

https://m.esa.int/Our_Activities/Space_Engineering_Technology/World-first_firing_of_air-breathing_electric_thruster

 

Regards,

Northstar

But power is the problem to get a newton of thrust at a exhaust velocity of 210000

N = 2 * 0.8 * p /210000

in essence you need 100kw per Newton, this is untenable, you would create more drag with the solar panels than thrust to get out of orbit. 

[Northstar1989]

On 3/25/2018 at 10:06 PM, PB666 said:

But power is the problem to get a newton of thrust at a exhaust velocity of 210000

N = 2 * 0.8 * p /210000

in essence you need 100kw per Newton, this is untenable, you would create more drag with the solar panels than thrust to get out of orbit. 

You're not trying to get *out* of orbit, just maintain an orbit- which can be done with a few dozen millinewtons of thrust for most satellite designs...

Even something the size of the ISS could maintain orbit at 200 km with less than a newton of thrust- which its panels provide enough power for...