Author Topic: Aerojet cite Solar Electric Propulsion as an enabler for an Exploration Gateway  (Read 13593 times)

Online Chris Bergin

http://www.nasaspaceflight.com/2012/01/aerojet-solar-electric-propulsion-enabler-exploration-gateway/

Part 1 of an interview with Aerojet's Julie Van Kleeck, Aerojet Vice President, Space & Launch System.

Hat tip to Aerojet senior comms' Jessica Pieczonka, who's totally awesome! :)

Online Chris Bergin

Bigger image of the Aerojet EP fleet - click to enlarge:
« Last Edit: 01/30/2012 10:37 PM by Chris Bergin »

Offline Jason Sole

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A lot cheaper than a load of prop depots. Excellent. I like what they are thinking.

Offline Patchouli

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A lot cheaper than a load of prop depots. Excellent. I like what they are thinking.

Solar electric and depots are anything but mutually exclusive instead they're complementary technologies.

If any thing the presence of a depot would build an argument for a good SEP cargo ferry.

Use of a SEP tug would make a depot at L1 easier and cheaper to run by allowing more efficient use of the payload.

It also can allow structures to be built in the safer LEO environment and then moved to higher orbits.

« Last Edit: 01/30/2012 11:25 PM by Patchouli »

Online Chris Bergin

Yep, note the "reduce the need" - not "instead of".
« Last Edit: 01/30/2012 11:42 PM by Chris Bergin »

Offline Lee Jay

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Isn't radiation the "elephant in the room" for any of these approaches?

Offline RocketmanUS

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Using SEP what would the travel time from LEO to L1 be for the ISS-ep( same ? for L2 )? ( a general estimation in days )

Delivery of a fuel tank with fuel at a mass of 77mt take from LEO to L1 for SEP?

 ( a general estimation in days for both questions )

Size of SEP system will determind travel time so using size of SEP for ISS-EP.

For such a large item as SEP and ISS-EP how easy is it to navigate out of LEO thru GSO objects?

Offline notsorandom

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Isn't radiation the "elephant in the room" for any of these approaches?
Most of what I have read indicates that it is not too difficult of a problem. I did a quick bit of searching and found an article written on the subject by Robert Zubrin of Mars Direct fame. Regardless of his other proposals and ideas he has a PhD in nuclear engineering so I would imagine he would speak with some authority on the subject of radiation safety.
http://www.spacedaily.com/news/mars-general-03w.html :
Quote
With easily manageable shielding techniques requiring no additional mission mass, such as proper placing of crew supplies within the spacecraft for shielding purposes, and the placement of sand bags on the roof of the hab during the stay on Mars, this dose could be readily cut in half. Such a 63 Rem (0.315 Sievert) dose would represent about a 1 percent incremental risk of future cancer to each member of the crew, roughly half the threat posed by sustaining a smoking habit over the same 2.5 year period.
Additionally in the article he points out some Mir cosmonauts received significantly higher doses on their missions. Additional shielding isn't too complicated either. Substances with a lot of hydrogen would work well, such as plastics, water and propellant. It a matter of adding more mass to the habitat.

Offline tigerade

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Ok, I read the article but don't really understand it.  How big of a deal is this?  Is SEP significantly more efficent than chemical propulsion?  If so, what are the exact advantages (in english)?

Offline yg1968

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Ok, I read the article but don't really understand it.  How big of a deal is this?  Is SEP significantly more efficent than chemical propulsion?  If so, what are the exact advantages (in english)?

Here is a partial answer to your question. It reduces the need for chemical propulsion by 2X for in-space propulsion.

From the article:

Quote
“The dramatic reduction in in-space propellant requirements enabled by SEP results in a 2X reduction in launcher delivery requirements to complete a mission, which will reduce the need for architectures like propellant depots.”

« Last Edit: 01/31/2012 12:33 AM by yg1968 »

Offline RocketmanUS

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Ok, I read the article but don't really understand it.  How big of a deal is this?  Is SEP significantly more efficent than chemical propulsion?  If so, what are the exact advantages (in english)?

Here is a partial answer to your question. It reduces the need for chemical propulsion by 2X for in-space propulsion.

From the article:

Quote
“The dramatic reduction in in-space propellant requirements enabled by SEP results in a 2X reduction in launcher delivery requirements to complete a mission, which will reduce the need for architectures like propellant depots.”


Reuse of SEP system after cargo or fuel delivery to L1/2 or other locations. Saves money on new propulsion system and fuel tank. For the cargo canister it could possibly be reused too.

Fuel depot or fuel transfer proposals look at reusable tankers ( Earth surface to LEO ).

The more that is reused the more money that is saved for other uses.

Use chemical propulsion if you need it there fast for L1/2 or LLO ( like for crew ).
« Last Edit: 01/31/2012 02:06 AM by RocketmanUS »

Offline tigerade

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Ah, that is very neat.  :)  I would support such a thing then as an aid to exploration.  I already like the idea of a exploration gateway platform as mentioned before.

Online Chris Bergin

Ah, that is very neat.  :)  I would support such a thing then as an aid to exploration.  I already like the idea of a exploration gateway platform as mentioned before.

Yep, love the idea of the gateway too. Never hurts to have options to get it out there and support, and here's one from Aerojet.

Offline kcrick

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Nice !  Another fine exploration article !

Keep em coming !  :)
Kevin

Online Chris Bergin

Nice !  Another fine exploration article !

Keep em coming !  :)

Thanks very much! :) Lots coming. I think I worked out I've got content for seven more right now (as in right now, more will come in for write ups in the meantime).

Offline STS Tony

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Nice work Aerojet! Didn't know about the satellite rescue, and any current tech which can work to help make this gateway become a reality is a good thing.

Online Robotbeat

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Isn't radiation the "elephant in the room" for any of these approaches?
No, it just is one thing in the whole system engineering trade. Everyone working on it is aware of it and detailed studies always take it into account. It's intended for cargo, not for humans (at least, not initially).

I should also point out that SEP is especially helpful for pushing an already-deployed Exploration Gateway from LEO (such as from ISS, if the gateway is assembled and deployed and initially tested there) to a Lagrange point compared to chemical propulsion. The reason for this is that a large deployed space station does not like the large acceleration and large bending moments caused by the much higher thrust of a chemical propulsion stage. Small pushes like those which are done for orbital maintenance of ISS are okay, but a big rocket engine would cause large stresses on interfaces between modules and on the radiators and the solar arrays. Relying on a large chemical rocket would cause greater design constraints. Of course, you could have a relatively low thrust chemical rocket do the boost, but then you have a much higher delta-v requirement because you wouldn't be able to take advantage of the Oberth effect. Not only that, but smaller chemical engines usually aren't quite as efficient. So, that would end up multiplying the IMLEO requirements.

On the low end of the 25-40kWe SEP tug, you might even be able to use the gateway's solar arrays and power regulating equipment. The tug could be just a docking port, tanks, electric thrusters (on a gimbal, probably), and a PPU. Though then you need solar arrays for a follow-on logistics tug. But just think about it.... You could push Cygnuses launched on Taurus II all the way to the gateway in the lunar vicinity. Or unmanned Dragons launched on Falcon 9. Or extra modules for the gateway. Or a propellant load for a reusable lander. Or a propellant load for a deep space mission of some sort (Mars Transfer Vehicle). Really powerful.

Aerojet is working on the NEXT thruster, which is like the NSTAR thruster used on Dawn right now, but a lot more efficient, capable of higher power, higher Isp, and much longer lifetime. And, I believe, it has better specific power than NSTAR as well. Really, it's probably the best thruster for this application and is as proven as anything else which hasn't actually gone to orbit, yet (it has completed over 30,000 hours of testing on a single unit in 2010). NSTAR was ground-tested to over 30,000 hours and showed no signs of failure. Since NEXT is supposed to be a better version of NSTAR, NEXT should have an even longer lifetime.

I'm definitely looking forward to whatever Aerojet has up their sleaves with solar electric propulsion for logistics... Maybe something like Cygnus but with larger UltraFlex arrays (these are very, very lightweight solar arrays... capable of something like 15kW per wing and a specific power of 150W/kg) and an SEP subsystem. Falcon 9 or the smallest Atlas V should be enough to push that with a full load (the longer Cygnus version) all the way to an EML1 gateway with the help of electric propulsion. And a single Atlas V 552 should be able to put an Apollo LM-sized lander and a sufficiently large SEP stage in LEO so that the whole thing could be put in LLO. Would be great for logistics for a lunar base or mission.

Great article, Chris! SEP is a great technology, even if it's not as flashy. It just keeps getting better, though. Slowly but surely. ;)
« Last Edit: 01/31/2012 05:27 AM by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Patchouli

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Isn't radiation the "elephant in the room" for any of these approaches?

It's an issue but not a show stopper.

The solar cells are not ruined by a single trip.
The worst of Smart 1's solar cell degradation ended after 2 months.

If necessary a solar Stirling or solar Rankine cycle setup can be used in place of solar cells and this is about as radiation tolerant as you can get.
Plus it can in theory offer a better power to weight ratio then silicon cells.


« Last Edit: 01/31/2012 06:55 AM by Patchouli »

Online Robotbeat

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...
Plus it can in theory offer a better power to weight ratio then silicon cells.
No, it can't. At least not better than photovoltaic in general.

And there are several options for radiation hardening of solar cells. Thin film cells are inherently radiation tolerant (even without shielding) and can actually heal themselves of radiation damage through annealing.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Patchouli

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...
Plus it can in theory offer a better power to weight ratio then silicon cells.
No, it can't. At least not better than photovoltaic in general.

And there are several options for radiation hardening of solar cells. Thin film cells are inherently radiation tolerant (even without shielding) and can actually heal themselves of radiation damage through annealing.

I was thinking with inflatable mirrors based off this technology.

There still would be the mass in the radiators.

The biggest disadvantage though would be moving parts.

But a big advantage it would allow a solar thermal rocket as well for higher thrust maneuvers lower in orbit.
« Last Edit: 01/31/2012 06:50 AM by Patchouli »

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