Refueling Ion Drive from Atmospheric Scooping

[adrianwyard]

I agree escape velocity is a bit much to hope for, but how about propellant-less plane changes? If possible that would be a big deal.

I'm not sure if it would be better to just thrust off-axis, or descend into very slightly thicker air to make the change with the help of aerodynamics and then (slowly) thrust your way up again once in the new plane.

[sanman]

ESA's new electric thruster harvests atmospheric ions:

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

[chipguy]

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

I wonder what fraction of satellite cross sectional area to the direction of motion has to be intake
for thrust to match or exceed drag.

I guess it depends on the ratio of the velocity at which air molecules/atoms impinge on the windward
face of the satellite to the velocity they exit the thruster. The former is basically orbital velocity.

If the thruster ISP is 2000 s then that is an exit velocity of ~19600 m/s vs ~8000 m/s orbital velocity
which suggests 8000/19600 or at least 41% of the front of the satellite has to be intake to cancel
drag.

Anyone see any flaws in this logic?

[speedevil]

If the thruster ISP is 2000 s then that is an exit velocity of ~19600 m/s vs ~8000 m/s orbital velocity
which suggests 8000/19600 or at least 41% of the front of the satellite has to be intake to cancel
drag.

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.

[Asteroza]

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

Interesting that this takes on a beehive inlet, rather than some designs which use a hypersonic cone.

[jee_c2]

...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.

I was wondering, that solar panels could be used in this case for steering (changing direction - plane change)  like sails in the wind of the very thin upper layer atmosphere.

Also, in some cases solar panels (and their drag) should be minimized, when the sat is "submerged" (densest environment). Could some battery (or supercapacitor) help in these time frames? Only the question of capacity, and the power consumption of the engine (and onboard systems).

BTW, minimum drag can be achieved by turning the solar panel with it's edged in the direction of the movement. This can also be optimal, if your plane of orbit is orthogonal to the direction of the Sun. (which are polar orbits, mostly)

[sanman]

Interesting that this takes on a beehive inlet, rather than some designs which use a hypersonic cone.

Maybe that's to maximize the charge coupling with the incoming atmospheric stream?

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.

[speedevil]

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.

Macroscopic orbital debris is also going to be very small.

[sanman]

So will these lowest-altitude orbital slots become the most coveted orbital space above Earth?

Will we see some kind of technological race to enable lower and lower orbits, with satellites becoming more and more streamlined to reduce atmospheric friction, and equipped with better and better performing electric thrusters to maintain those orbits against deterioration?

If so, then it sounds like an interesting niche to specialize in, regarding satellite construction.

Such a trend would also help to mitigate the space junk problem, since there's relatively less danger of such lower orbiting satellites producing junk that stays up for a long time.

From cubesats to "tubesats"?

[speedevil]

So will these lowest-altitude orbital slots become the most coveted orbital space above Earth?

At some fairly rapid point, the gains you get from being closer are outweighed by the operational cost.
A satellite at (say) 150K may be quite plausible technically, but is going to be ten times the drag as at 200km.
Ten times again at 120.

You also need way more satellites per constellation as the footprint goes down.

[alexterrell]

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?

This concept could have more value in the far future where large orbiting space craft need millions of tons of nitrogen for their atmosphere. But for now, there is a feeling that more launches is easier than more complexity.

[sanman]

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.

[speedevil]

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.

Drag in this case is essentially not as it is with normal aerodynamics, but is purely the frontal area of the satellite - due to the atmospheric molecules moving so fast compared to the speed of sound.

So, extending the solar panels back along the orbit (or indeed forward) is free, drag-wise.
You want them to be edge-on to the oncoming flow.
You can of course spin them (or the craft) around the velocity vector in order to point them at the sun, and end up with around half of the average solar input you might otherwise get with fully pointed at the sun panels.

[dror]

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

[speedevil]

+ 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

The 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.

[Asteroza]

+ 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

The 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...

[rakaydos]

+ 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

The 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...

IIRC, JP is relying on some expirimental, in the lab methods of actively reducing drag, to work at least 60% of the in the lab theoretical values. Also they reduce the need for hypersonic lift via atmospheric displacement...

[indaco1]

I think Oberth effect makes things even more difficult for elliptic orbit scooping.

[eugenio.ferrato]

To whom it may concern,

 I link you to two interesting article recently published on the topic:

Development and Experimental Validation of a Hall Effect Thruster RAM-EP Concept (IEPC-2017-377)==>
https://iepc2017.org/sites/default/files/speaker-papers/iepc-2017-377_ram_final.pdf

and

Conceptual Design of an Air-Breathing Electric Thruster (IEPC-2015-271) ==>
http://erps.spacegrant.org/uploads/images/2015Presentations/IEPC-2015-271_ISTS-2015-b-271.pdf

Moreover, an other article on this topic (ID:0431) will soon be released for the Space Propulsion 2018 Conference (to be held on May 14th-18th 2018 in Seville, Spain).

All the best,

Eugenio

[LMT]

SpaceX Trawler

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?

Or conceivably you could combine the two concepts, using ITS as the "scoop", and using a marshalling yard as the "mother ship".  That might make economic sense.

--

At 250 km a notional km3 marshalling yard with ISEP booms of Voronka et al. 2006 could generate thrust roughly an order of magnitude greater than the deceleration of atmospheric drag.  Thrust exceeds requirement.  How might excess thrust be used to good effect?

One possibility:  a SpaceX trawler

Trawling lowers a collector system from orbit, to scoop O2 from the thermosphere and deliver it to the orbiting platform as LOX. 

Benefit: 78% tanker reduction

Where trawlers deliver all LOX for LEO burns, tankers deliver only LCH4.  This results in a 78% cut in tanker payload mass, corresponding with a 78% cut in the number of required tanker launches.

It’s an old idea, but of course trawler drag is a vexing problem.   For this reason the great and propellant-free propulsion of an ISEP marshalling yard would offer an opportunity to bypass the old problem, and realize the benefits of atmospheric trawling. 

Parameters

What are the environmental parameters of the new problem?  First-pass:

To minimize the temperature inside the trawler inlet, one might scoop where the atmospheric temperature is lowest:  at 90 km, ~150-200 K.  Even so, the scoop’s compression shock would be hot:  600-900 C.

Some compression energy dissociates O2 and N2, producing atomic oxygen and nitrogen.  Atomic oxygen reacts with polymers, so heat shielding or other inert coatings must be applied to all polymer surfaces.  Fortunately the temperature is not high enough to ionize much, so at 90 km the trawler can maintain radio contact with the marshalling yard.

At 90 km the spacecraft’s split flaps should have good control authority, to maintain nose-forward orientation without expending propellant.

Pressure is ~0.2 Pa, density 3.4E-6 kg/m3, O2 mass fraction 23%.  Therefore an inlet of 100 m2, having capture efficiency of 90%, can fill the 860-ton LOX tank in 3 weeks.

How might the trawler be structured?

Conceivably a SpaceX ITS cargo ship could be fitted out at the marshalling yard with a trawler “kit”:  a tethered fabric inlet and cooler/compressor system.  The inlet would feed gas into the cooler, inside the cargo bay.  The cooler would feed a centrifugal compressor that separates LOX from gaseous N2, and then feeds LOX into the zero-boil-off (ZBO) unit’s LOX line, to fill the tank.

A trawler kit might look something like this:



In this modified SpaceX image the open cargo bay sports a trawler kit, in blue.  The inlet is defined by the layer of fabric connecting the two halves of the hinged fairing.  Inside, an inflated dual cone plug compressor maximizes the pressure and mass at the end of the inlet. 

The cone tip provides an attachment point for the tether, perhaps an interconnected hoytether, which extends 160+ km to the marshalling yard.  The marshalling yard lowers and lifts the trawler by the tether, using a pass-through gripper-wheel mechanism such as that proposed for the ISS in Vas et al. 2000.

Tether and inlet might be fabricated from 3M Nextel ceramic textiles, which have been used on space shuttles. 



These flexible ceramic products resist atomic oxygen and have both low thermal absorptivity and high emissivity.  They also benefit from “heat treating” at 900 C, which “improves the chemical resistance, anneals the stress from the fiber, and increases the modulus or stiffness of the fiber”, according to the product technical reference guide. 
 
To cool and liquefy O2, one might adapt Reaction Engines’ SABRE technology, as presented in Davies et al. 2015. 




 
The SABRE pre-cooler has been designed to cool Mach 5 air at 25 km, lowering it from 1000 C to 123 K. 


 
The SABRE turbo-compressor, or centrifugal compressor, has been designed to compress the cooled air to 14,000 kPa.  Heat from the pre-cooler drives the compressor, for high efficiency.

The trawler scenario presents different operating conditions of course.  Inlet air is cooler, inlet pressure is lower, and the final compressor output temperature and pressure are lowered to produce LOX (temperature around 80 K with pressure slightly above 150 Pa).   LOX flows over the diffuser surface into the manifold collector, where it’s pumped into the ZBO LOX line for storage in the LOX tank.

The compressor’s temperature and pressure hold N2 in gas phase.  N2 could pressurize the dual cone plug.  Notably, drag at this low altitude (10-20,000 N) is too great to be countered with ion engines, so the remaining nitrogen would not be used for propulsion.  It could be circulated as a supplemental coolant, before venting. 

As it happens, I had opportunity recently to meet with a Reaction Engines engineer and discuss adaptation of SABRE hardware to LOX trawling.  His initial impression was that the requirements were not a great challenge; they could be met with relatively minor modification of existing SABRE hardware.  So perhaps SABRE provides a first, known reference point for consideration of alternate coolers and compressors.  One option to explore:  adapt the compressor of the ZBO system to take over the role of the SABRE turbo-compressor, to perform both ZBO compression and trawler turbo-compression with the same hardware.  (N2 removal would be a new task for a ZBO compressor.)  Or vice versa.

Power

Electric pumps could run off ITS deployable solar panels, and ITS batteries at night.  However solar panels would need to be augmented with something akin to a hinge joint at the base, to rotate each panel unit parallel to the flight path and minimize drag.  Otherwise total drag on the vehicle could become excessive.  Alternately solar panels might be deployed from the cargo bay, behind the inlet.

Trawler Fleet

This basic configuration might allow two SpaceX trawlers to operate concurrently, with drag not exceeding the marshalling yard’s drag-compensation thrust.  However, conceivably an additional, much larger solar panel could be unfurled from each trawler, trailing behind, to provide greater electric potential and current.  Current electrons (PV + ionosphere electrons) would be directed up the tether through conductive strands, to give additional electrodynamic thrust; reducing orbit-averaged trawler deceleration, or, ideally, zeroing it out.  Notionally ISEP “needles” could be added to the trailing panel (which is likely much longer than the spacecraft itself) to apply torque and lift, so as to maintain the panel’s low-drag, edge-on orientation.  Likewise, the terminal 20 km of tether could be designed not as a hoytether but as a thin tape, with ISEP needles added for electrodynamic torque.  ISEP would hold that tether segment edge-on, minimizing tether drag where it would otherwise be very great.
 
If drag-canceling methods were successfully implemented, the marshalling yard could deploy trawlers without concern for drag.  It could deploy as many trawlers as might be supported concurrently by tether mechanisms, as a “trawler fleet”.



Refs

Davies, P., Hempsell, M., & Varvill, R. (2015). Progress on Skylon and SABRE. IAC-15-D218.

Vas, I. E., Kelly, T. J., & Scarl, E. A. (2000). Space station reboost with electrodynamic tethers. Journal of spacecraft and rockets, 37(2), 154-164.

Voronka, N. R., Hoyt, R. P., Slostad, J., Gilchrist, B. E., & Fuhrhop, K. (2006). Modular spacecraft with integrated structural electrodynamic propulsion. NASA Institute for Advanced Concepts.