Author Topic: ALTERNATIVE - NON SLS: Exploration Gateway Platform - Reusable Lunar Lander  (Read 98210 times)

Offline MATTBLAK

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Sizing reactors for various launchers would get you power generation in various classes, of course. An SLS launched reactor should get you something in the 100kw range. One launched on a Falcon Heavy - probably less than 50kw. A standard EELV? That's trickier, but the old Soviet 'Topaz' reactor only rated about 5kw and back then they only had Soyuz and Proton launchers - as they do now. Look at Submarine reactors and their required shielding - all that can come to a couple hundred tons; all for powering their high-tech steam engines!

For Martian or other ISRU, we couldn't tolerate that kind of bulk, so reactors need scaling-down for space applications, resulting in inevitable lower power outputs. Seems to me; investigating higher-efficiency solar arrays, coupled with Stirling engines and maybe R.T.G. top-up might be cheaper, safer, albeit slower and less powerful alternatives.

So steering this back to non-SLS Platforms and what equipment might get there via various EELVs: its feasible that a small fission reactor - in the 5-to-10kw class - could be placed at a Gateway Station to await loading aboard a Mars Expedition vehicle - just as the propellant from a Depot would be. As a Gateway Station should have plentiful solar power available for its needs, a reactor would be superfluous. Unless of course another Gateway Station was needed in or near the Asteroid belt, or maybe at the Martian moons to help crack volatiles for propellant production. Besides, if the launchers are so 'small', the above mentioned alternatives would be the 'bootstrap' options EELVs force upon us. Not such a bad thing, in the long run, I suppose!
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Offline Robotbeat

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I think a small fission reactor for Martian ISRU may be feasible (deployed well away from the crew and behind a hill so it didn't need shielding... also, it could benefit from convection cooling unlike in a true vacuum)... But it'd likely be much more expensive than some sort of solar array. Which is a better deal probably also depends on other factors, like availability of Pu-238 for RTGs for backup crew power and the actual cost and payload capability of landing stuff on Mars and expected rate of dust deposition (and random cleaning). If you had people on the surface (or a good telepresence), you could have just a really long roll of thin-film solar cells that you roll out and maybe place rocks on them to keep it from being blown away by the wind.

And I think we'll likely end up not being able to land something on Mars (or the Moon) more massive than 25mT for a long time.
« Last Edit: 01/07/2012 07:30 am by Robotbeat »
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Offline MATTBLAK

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Yes. The state-of-the-art in landing mass on Mars is about 1.5 metric tons right now. 'Red Dragon' if and when it goes ahead will raise that standard to slightly more than 4 metric tons. The lightest possible vehicle that could land a crew of 4 on Mars with their equipment would easily be more than 20 metric tons, perhaps closer to 30.

And even with aeroshell braking and parachutes, the majority of braking from supersonic speed to touchdown will still be propulsive. Storables or cryogenics? That's for another thread, another time.
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Online mmeijeri

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Sizing reactors for various launchers would get you power generation in various classes, of course. An SLS launched reactor should get you something in the 100kw range. One launched on a Falcon Heavy - probably less than 50kw. A standard EELV? That's trickier, but the old Soviet 'Topaz' reactor only rated about 5kw and back then they only had Soyuz and Proton launchers - as they do now.

Huh, why do you think reactors would be massive? SAFE-400 (100kWe) would be 1200kg. The generators and shielding would be much heavier, but generators could be transported separately and the shielding could use local materials.
« Last Edit: 01/07/2012 10:04 am by mmeijeri »
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Offline MATTBLAK

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EDIT: *What I failed to mention in my earlier post was that my Sub reactor analogy was a bit flawed - some readers might not be aware that Sub reactors produce Megawatts of power, not the 'mere' Kilowatts that would be adequate for many space missions. In hindsight, this could look like a Strawman argument put up by me to prey on some readers unfamiliarity with huge, heavy Sub reactors or nuclear reactors in general. I'm surprised Chuck Longton didn't take me to task!!*

Well, I suppose if there is a tele-robotic bulldozer or grader there to cover it with regolith, there's your shielding! Of course, there's the need to get that machine there first.

Admittedly, I knew very little about the SAFE-400 and looked it up: Brayton turbines! I hope they'd use silicon-nitride bearings for long life ;) My Google also told me about the HOMER-15 concept which would be very compact at about 215kg and produce about 15kw. That kind of power would easily run a 3 bedroom house, let alone a spacecraft. THIS is the kind of tech that should be funded, but the nuclear bogey-man trumps all, eh? :(
« Last Edit: 01/08/2012 02:19 am by MATTBLAK »
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Offline Solman

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Well, I suppose if there is a tele-robotic bulldozer or grader there to cover it with regolith, there's your shielding! Of course, there's the need to get that machine there first.

Admittedly, I knew very little about the SAFE-400 and looked it up: Brayton turbines! I hope they'd use silicon-nitride bearings for long life ;) My Google also told me about the HOMER-15 concept which would be very compact at about 215kg and produce about 15kw. That kind of power would easily run a 3 bedroom house, let alone a spacecraft. THIS is the kind of tech that should be funded, but the nuclear bogey-man trumps all, eh? :(

 Actually there are sound practical reasons why nuclear tech such as you recommend be funded, are not funded.
 The most notable is cost - which is truly astronomical.
Next is reliability - the generators have many moving parts and reactors must be constantly managed. 
Beyond that is specific power. The HOMER-15 concept you mention needs over 14kg to produce 1 KW elec.!  Is there a solar panel for space use that is that poor a performer?
Now nuclear works the same at any distance from the Sun unlike solar PV, but there is a way to at least partly compensate for this.
Large concentrator mirrors (an example of which flew on STS-77 as an antenna but would have worked as a solar concentrator if aimed at the Sun ) would cost much less than anything nuclear and can make up for the inverse square deficit to a huge extent. Such mirrors focus kilowatts per kg and are nowhere near what physics allows at their current state of development. Orders of magnitude improvement is theoretically possible.
Triple junction PV for concentrated sunlight has no moving parts, 40% or better efficiency, and I once tracked down a specific power for them in the Spectrolab literature of 666W/kg for these systems but I can no longer find this. If that is roughly correct, then they are nearly ten times higher in specific power than the HOMER-15.
At any rate, you can buy them today at a very tiny fraction of what any nuclear system would cost and the nuclear system would require years of development.
When JIMO was still alive I was told that solar was impractical at Jupiter - then came JUNO. The reactor, generator, radiator and related equipment for JIMO massed roughly 10,000 kg. for 100 KW electric or 100kg/KWelec. The cost was 9 billion and the development time several years. You could send a lot of JUNO's to Jupiter at that cost.

Don't blame politics - blame physics/engineering for nuclear's absence.

Steve

Offline MATTBLAK

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This is part of the reason why I've never been convinced of the absolute need for big nuclear on Mars missions - other than raw power for cracking lots of volatiles for ISRU propellant - lots are needed to lift off from Martian surface.

Solar concentrators, advanced arrays using gallium-arsenide (yes, expensive) along with advanced RTGs and Stirling engines - all these can be added to the arsenal of technologies needed to leverage, boostrap - pick your adjective - if funding is not around for big, Heavy Lift vehicles and raw, nuclear power. With only Medium-Heavy lift, we have to be more clever and resourceful with funds and the technologies that are mission enablers. All the above, although appearing to be a bit off-topic and digressions, are actually inter-related when we have to consider what we are forced to use when confronted by reality: With off-the-shelf rocketry and no money for brute-force power systems, NASA and others have got to get smart; smarter than they already are.
« Last Edit: 01/08/2012 02:12 am by MATTBLAK »
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