Author Topic: Sun shade for orbital propellant depots  (Read 7275 times)

Offline sandrot

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Sun shade for orbital propellant depots
« on: 02/20/2007 03:19 PM »
Has a sun shade (similar to JWST's) ever been considered to reduce propellant boil-off in an orbital propellant depot?
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Offline AntiKev

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Re: Sun shade for orbital propellant depots
« Reply #1 on: 02/20/2007 03:25 PM »
I don't know that it's ever been considered.  What is more likely is shipping water to the facility, and then using solar power to perform electrolysis on orbit.  Basically make the propellant on demand, or two to three days prior to the customer's arrival, and then condense it.  Since you have the condensation facilities on board, you can actually re-condense the boil-off, mitigating the concern.

Offline sandrot

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Re: Sun shade for orbital propellant depots
« Reply #2 on: 02/20/2007 03:45 PM »
Is electrolysis viable? It doesn't seem to work that well on the Elektron unit.

I was thinking of a "shade-station", where the big dumb tank would dock and sit waiting. It would be discarded when empty.
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Offline Jim

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Re: Sun shade for orbital propellant depots
« Reply #3 on: 02/20/2007 03:49 PM »
Quote
AntiKev - 20/2/2007  11:25 AM

I don't know that it's ever been considered.  What is more likely is shipping water to the facility, and then using solar power to perform electrolysis on orbit.  Basically make the propellant on demand, or two to three days prior to the customer's arrival, and then condense it.  Since you have the condensation facilities on board, you can actually re-condense the boil-off, mitigating the concern.

That is impractical.   It would take too much power to do it that quickly and to liquify H2.  Easier to send it up in a cryogenic state

Offline sandrot

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Re: Sun shade for orbital propellant depots
« Reply #4 on: 02/20/2007 05:10 PM »
Not to mention the additional radiators, pumps, filters, solar panels, batteries...
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Offline meiza

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Re: Sun shade for orbital propellant depots
« Reply #5 on: 02/20/2007 05:30 PM »
In leo earthshine also warms you up. I don't know if that is how serious for LOX.

Offline Marcus

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Re: Sun shade for orbital propellant depots
« Reply #6 on: 02/20/2007 06:36 PM »
Is the L-2 point in the Earth's shadow or is it too small (in terms of degrees occluded) at that distance to eclipse the sun? That far away, the infrared radiation from earth should be infintesimal. Unfortunately, I bet the % of the solar disc occluded is also infinitesimal. :(
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Offline Tom Ligon

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Re: Sun shade for orbital propellant depots
« Reply #7 on: 02/20/2007 06:41 PM »
NASA is expert in using metalized films as solar shields.  I believe the gold stuff is particularly effective at IR.  You could probably shield a huge facility with a kg or two of the stuff.

All the old Apollo/LEM stuff looked like it was made of tinfoil due to liberal application of it.

Offline sandrot

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Re: Sun shade for orbital propellant depots
« Reply #8 on: 02/20/2007 08:23 PM »
Quote
Marcus - 20/2/2007  2:36 PM

Is the L-2 point in the Earth's shadow or is it too small (in terms of degrees occluded) at that distance to eclipse the sun? That far away, the infrared radiation from earth should be infintesimal. Unfortunately, I bet the % of the solar disc occluded is also infinitesimal. :(

I am talking of a solar shade attached or very close to the fuel depot, as it happens on JWST.

BTW the sun shade for JWST is layered, I wonder what is it made of?
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Offline Jim

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Re: Sun shade for orbital propellant depots
« Reply #9 on: 02/20/2007 08:28 PM »
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sandrot - 20/2/2007  4:23 PM

Quote
Marcus - 20/2/2007  2:36 PM

Is the L-2 point in the Earth's shadow or is it too small (in terms of degrees occluded) at that distance to eclipse the sun? That far away, the infrared radiation from earth should be infintesimal. Unfortunately, I bet the % of the solar disc occluded is also infinitesimal. :(

I am talking of a solar shade attached or very close to the fuel depot, as it happens on JWST.

BTW the sun shade for JWST is layered, I wonder what is it made of?

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Offline sandrot

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Re: Sun shade for orbital propellant depots
« Reply #10 on: 02/20/2007 09:01 PM »
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Jim - 20/2/2007  4:28 PM

Mylar

I guess the same material as the old LEM.
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Offline nacnud

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Re: Sun shade for orbital propellant depots
« Reply #11 on: 02/21/2007 12:18 AM »
I've wondered this too, I see no reason why it wouldn't work for liquid oxygen that boils at 90K, however liquid hydrogen boils at 20K I'm not sure that even if shielded from sunlight that LEO doesn't have enough incidental radiation to raise a bodies temperature more than that.

Offline Bill White

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Re: Sun shade for orbital propellant depots
« Reply #12 on: 02/21/2007 12:30 AM »
Boil off is a good reason, IMHO, to strongly consider LOX & CH4 rather than LOX and LH2 for on orbit propellant depots.

LOX and kerosene? Largely avoiding cryogenic issues at least for the kerosene could save infrastructure costs traded against lower ISP.
EML architectures should be seen as ratchet opportunities

Offline Jim

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Re: Sun shade for orbital propellant depots
« Reply #13 on: 02/21/2007 12:52 AM »
Quote
Bill White - 20/2/2007  8:30 PM

Boil off is a good reason, IMHO, to strongly consider LOX & CH4 rather than LOX and LH2 for on orbit propellant depots.

LOX and kerosene? Largely avoiding cryogenic issues at least for the kerosene could save infrastructure costs traded against lower ISP.

Cryogens have a natural pumping mechanism.  RP-1 would require high pressure gases and/or compressors

Offline Bill White

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Re: Sun shade for orbital propellant depots
« Reply #14 on: 02/21/2007 01:56 AM »
Quote
Jim - 20/2/2007  7:52 PM

Quote
Bill White - 20/2/2007  8:30 PM

Boil off is a good reason, IMHO, to strongly consider LOX & CH4 rather than LOX and LH2 for on orbit propellant depots.

LOX and kerosene? Largely avoiding cryogenic issues at least for the kerosene could save infrastructure costs traded against lower ISP.

Cryogens have a natural pumping mechanism.  RP-1 would require high pressure gases and/or compressors

Thus, the trade-offs need to be examined before choosing LH2 or CH4 or perhaps even fuels such as propane or kerosene.
EML architectures should be seen as ratchet opportunities

Offline sandrot

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Re: Sun shade for orbital propellant depots
« Reply #15 on: 02/21/2007 02:10 AM »
I was further reading about this JWST sun shade. Thanks to it instrumentation can reach temperatures of 30 to 50 K.

So it seems the same sun shade concept can be good for LOX, I don't know for LH2 unless the tank can withstand increased pressures.

For your curiosity:
http://www.stsci.edu/jwst/overview/design/sunshade.html
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Offline Jim

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Re: Sun shade for orbital propellant depots
« Reply #16 on: 02/21/2007 10:56 AM »
Quote
sandrot - 20/2/2007  10:10 PM

I was further reading about this JWST sun shade. Thanks to it instrumentation can reach temperatures of 30 to 50 K.

So it seems the same sun shade concept can be good for LOX, I don't know for LH2 unless the tank can withstand increased pressures.

For your curiosity:
http://www.stsci.edu/jwst/overview/design/sunshade.html

That is at the JWST location, not LEO

Offline sandrot

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Re: Sun shade for orbital propellant depots
« Reply #17 on: 02/21/2007 12:56 PM »
Does it change that much on the "sunny" side?

I read remarks about earthshine heat contribution. how bad is it?
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Offline aftercolumbia

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RE: Sun shade for orbital propellant depots
« Reply #18 on: 03/15/2007 05:01 PM »
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sandrot - 20/2/2007  9:19 AM

Has a sun shade (similar to JWST's) ever been considered to reduce propellant boil-off in an orbital propellant depot?

Yeah...uh...well...sort of.  My current study is called Symtex, and as its maneuver stage, I'm looking at a passively cooled oxymethane propulsion system to compete with the oxyhydrogen Centaur ACES (might not compete commercially, because Symtex is quite a bit smaller.)  The ACES/ICES papers at www.lockheedmartin.com say that active cryocoolers are not worth it for in space propellant storage until you are looking at durations measured in months, perhaps years.  One can consider cooling/storage methods to come in three phases:

1. Passive (being shades, insulation, and radiators)
2. Semi-active (taking a cryogen that you have and expanding it to use its cooling ability before venting it into space)
3. Active (a closed cycle cryocooler, complete with compressors and electrical supply)

Active is needed for hydrogen, but it isn't for oxymethane.  The V-shield/radiator technology can make 60K on Planck.  This is cold enough to actually _freeze_ liquid methane, which does so at 90K.  A combination of MLI insulation and semi-active cooling should be able to make an oxymethane stage last for months on LEO, where V-shield radiators are ineffective because of this inconvenient 160deg angle heat source called Earth.

Quote
Is the L-2 point in the Earth's shadow or is it too small (in terms of degrees occluded) at that distance to eclipse the sun? That far away, the infrared radiation from earth should be infintesimal. Unfortunately, I bet the % of the solar disc occluded is also infinitesimal.
Quote

The penumbra of Earth's shadow is about 13000km in diameter.  Space telescopes planning to go there can avoid hitting it for six years, and then it's a 15m/s maneuver to avoid hitting it.  Lissajous orbits at L2 are about million km in diameter.

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