There wouldn't be much air to "scoop" in LEO, to get a good amount you'd probably want to be in the lower atmo.Xenon is pretty rare in the atmo, so since there's very little air in LEO, there's almost no Xenon up there.
Here's one major problem. If you dip your perigee into the atmosphere, the drag is going to decrease your apogee. And your next perigee is going to be back in the atmosphere again.The only way to raise your perigee out of the atmosphere is with a burn at apogee. But if you're using an ion drive, whch uses lowthrust over an extended time, you're not going to be able to manage a significant perigee boost before you're heading back down again. Your orbit is going to quickly degrade, until you end up re-entering and burning up.So, basically, the answer is "No."
...you 'burn' as you collect, so that you are at least counteracting your drag. Hall Effect, FRC, and Helicon thrusters have all shown to work on some combination of N2 and O2... you need an Isp that is at least the orbital velocity divided by all of your propulsive/collection efficiencies to make up for drag and more if you want to store...
We've looked at these air-breathing electric propulsion systems extensively. The ASPW (advanced space propulsion workshop) has featured several of these concepts, ours was a number of years ago. My view was this was tough, but maybe not impossible. As others have noted, the orbital mechanics is pretty easy as long as you 'burn' as you collect, so that you are at least counteracting your drag. Hall Effect, FRC, and Helicon thrusters have all shown to work on some combination of N2 and O2 (and maybe stored Xenon for the cathode). The basic idea as we understand it is you need an Isp that is atleast the orbital velocity divided by all of your propulsive/collection efficiencies to make up for drag and more if you want to store. At 100% efficiency and assuming your vehicle was a flow-through 'scoop' and stored nothing, you'd only need 800-ish seconds.But, with a 50% collection and pressurization efficiency, a 75% thruster mass utilization efficiency, and storing 25% of the gas each orbit you need an ISP of 2700 seconds. This assumes the entire front end of this thing is all scoop. I think the biggest concern is heat rejection and power. If your spacecraft is much bigger than the scoop/inlet (ie solar panels) the amount of thrust needed to counteract all of the drag gets a lot harder. And while the thruster puts most of its energy into the propellant, either heat or kinetic, the scoop doesn't have a natural way to loose energy.Cool stuff, I bet NIAC would want to take a look at this.-David
5 March 2018In a world-first, an ESA-led team has built and fired an electric thruster to ingest scarce air molecules from the top of the atmosphere for propellant, opening the way to satellites flying in very low orbits for years on end.ESA’s GOCE gravity-mapper flew as low as 250 km for more than five years thanks to an electric thruster that continuously compensated for air drag. However, its working life was limited by the 40 kg of xenon it carried as propellant – once that was exhausted, the mission was over. Replacing onboard propellant with atmospheric molecules would create a new class of satellites able to operate in very low orbits for long periods....
ESA's new electric thruster harvests atmospheric ions:http://m.esa.int/Our_Activities/Space_Engineering_Technology/World-first_firing_of_air-breathing_electric_thruster
If the thruster ISP is 2000 s then that is an exit velocity of ~19600 m/s vs ~8000 m/s orbital velocitywhich suggests 8000/19600 or at least 41% of the front of the satellite has to be intake to canceldrag.Anyone see any flaws in this logic?
...It's going to constrain your solar panel pointing a lot.In principle, you may be able to effectively steer the ions, which helps if you don't solely want to use it for drag cancellation.
Interesting that this takes on a beehive inlet, rather than some designs which use a hypersonic cone.
Anyway, it seems like these kinds of satellites would be suitable for the lowest orbits, and thus able to offer the sharpest imagery and the lowest communication latency with the ground.
So will these lowest-altitude orbital slots become the most coveted orbital space above Earth?
Gee, I'm imagining a flattened lenticular shape would be best for solar collection, as well as RF reception from below. It would also present a reduced cross-section for oncoming atmosphere. As long as your solar power is being used to boost the Isp, then don't you benefit from maximizing solar collection? On the other hand, you need to be able to coast through the nighttime phases without losing too much speed.
Depending on its efficiency it seems this could enable a number of things. What are the possibilities?A couple of obvious ones are:+ Lowest possible latency satellite links.+ Cheaper or better earth observation.But what else?Propellent-less plane changes? (Maybe slowly.)Military?
+ Self filling oxygen depot (to reduce the number of refueling flights or fill up station tanks)+ with a little stretch, a full on surface-to-orbit airplane
Quote from: dror on 03/08/2018 07:14 pm+ Self filling oxygen depot (to reduce the number of refueling flights or fill up station tanks)+ with a little stretch, a full on surface-to-orbit airplaneThe second really isn't plausible at all.This technology is several orders of magnitude too low thrust, and doesn't really scale meaningfully.Once you get to perhaps to 70km or so the plasma physics changes, and you can't simply accellerate the gas in the same way.Flying 'slowly' to orbit, you require hypersonic lift, which only comes with really high amounts of drag.This means your heatshielding problems get orders of magnitude worse, as well as your power requirements being utterly ridiculous.
Quote from: speedevil on 03/08/2018 07:46 pmQuote from: dror on 03/08/2018 07:14 pm+ Self filling oxygen depot (to reduce the number of refueling flights or fill up station tanks)+ with a little stretch, a full on surface-to-orbit airplaneThe second really isn't plausible at all.This technology is several orders of magnitude too low thrust, and doesn't really scale meaningfully.Once you get to perhaps to 70km or so the plasma physics changes, and you can't simply accellerate the gas in the same way.Flying 'slowly' to orbit, you require hypersonic lift, which only comes with really high amounts of drag.This means your heatshielding problems get orders of magnitude worse, as well as your power requirements being utterly ridiculous.JP Aerospace and their Ascender design begs to differ, but they are the epitome of slow boat methods. Then again, they haven't gone bankrupt either...
Hi, I started a similar discussion back in 2009:https://forum.nasaspaceflight.com/index.php?topic=17984.msg443506#msg443506 My concept was to have a scoop at low altitude, connected by a tether to a mother ship at about 350km altitude, where solar panels can work without excessive drag.I think what has changed since then is the promise of BFR reducing the costs of shipping fuel to orbit - so raising the question, why bother?
Quote from: chipguy on 03/06/2018 05:02 pmIf the thruster ISP is 2000 s then that is an exit velocity of ~19600 m/s vs ~8000 m/s orbital velocitywhich suggests 8000/19600 or at least 41% of the front of the satellite has to be intake to canceldrag.Anyone see any flaws in this logic?Something like that seems plausible. It's going to constrain your solar panel pointing a lot.In principle, you may be able to effectively steer the ions, which helps if you don't solely want to use it for drag cancellation.
Shouldn't we keep this on the title concept and leave out SABRE, multi-kilometer thethers, BFR, orbital debris removal, and the like?
I wanted to ask if there is a practical mass range for satellites to use air-breathing electric propulsion.Can electric air-breathing propulsion be scaled up or down across the board for a wide range of satellite masses?Can it be used on smallsats, including even nanosats?Or is this type of propulsion only suitable for heavier satellites? What's the threshold for mass?
The first aeroplane propelled by ionic wind
This is exciting. Doesn't it belong in a different thread, though?
Just another idea that suggests how atmospheric scooping could change the game, if it works.Refill a LOX depot at LEO by Atmospheric Scooping.Dock a reusable second stage (eg. BFS/Starship) and relox it to enable a much longer reentry burn and a low velocity reentry with reduced TPS requirements. LOX is the heavy part of propellant, (eg BFS old design 240000 kg CH4, 860000 kg LOX) so additional CH4 at launch is not so expensive in terms of payload penalty.
In order to ramscoop any useful quantity of O2, you would need to compensate for the apogee drop from that braking manoeuvre. That means either you need a rarefied airbreathing engine of sufficient thrust to overcome that drag (and enough excess thrust to collect some extra atmosphere to scavenge additional O2 from), or drag up enough propellant in the first place to use a rocket engine to keep your apogee up (in which case you may as well skip the scoop and just transfer that propellant instead!).
Here's one major problem. If you dip your perigee into the atmosphere, the drag is going to decrease your apogee. And your next perigee is going to be back in the atmosphere again....trim
But it might be the case that a propulsion system is needed to counteract the drag. There are solutions on the horizon for that, especially in the form of Atmosphere-Breathing Electric Propulsion (ABEP.)Though the atmosphere is very thin in VLEO, it’s still there. The oxygen in that environment can act as a propellant for ABEP systems. The problem is the low density.The ESA is working on an Air-Breathing Electronic Thruster, an ion drive that uses the atmospheric oxygen as a source of ions, with a satellite’s electrical power system providing the electricity. By doing that, the system doesn’t need to carry any xenon propellant, instead harvesting the atomic oxygen in VLEO.The problem, again, is the low density of that atomic oxygen. The ESA is developing a special intake for their thruster that would collect and compress the oxygen, making it viable as a propellant. The system has been tested successfully in simulated VLEO conditions.
Generalised concept of an atmosphere-breathing electric propulsion (ABEP) system.