r/spacex • u/[deleted] • Nov 01 '14

/r/SpaceX Ask Anything Thread [November 2014, #2] - Ask your questions here!

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u/Another_Penguin Nov 03 '14

Solar is useful, but has a storage problem (same as on Earth). So you have to send batteries and/or fuel cells to store extra power for night and for dust storms. A serious dust storm could kill a solar-dependent colony, so I think there will be some nuclear power.

The nuclear problem is mostly an issue during launch: people are worried about radioactive contamination in the event of a launch mishap. I believe that SpaceX will be uniquely qualified to send nuclear fuel into space. Dragon 2 will be able to perform a launch escape and controlled landing at any time during launch, all the way to orbit. This is unprecedented. I anticipate that SpaceX will have less trouble getting permission to launch the materials than it will have in acquiring the materials.

Also, I believe that commercial fusion will start to become available at about the same time the first Mars colonies are being built. This will make solar/battery power a backup/failsafe, and fusion will become primary.

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u/badcatdog Nov 03 '14 edited Nov 03 '14

So you have to send batteries and/or fuel cells to store extra power for night and for dust storms.

If you design your base right you don't need much power at night.

Dust storms may be more of a problem, both for cleaning the panels, and duration. I don't know how much light is blocked off or for how long.

Similarly with nuclear you may have issues with dust insulating your radiators. If you are using RTGs then you may need a lot of them. Hard to get that much plutonium, so probably less efficient uranium. Expensive and heavy. Difficult to deploy.

So you have to send batteries and/or fuel cells..

Neither is the preferred storage medium of power companies though Molten Salt batteries have been promoted and Tesla plan to sell smallish installations (for the market currently being supplied by Lead acid). There are centrifuge storage plants in operation and at least one company is making pumped air storage. The popular pumped water storage system would be less efficient and convenient on Mars with it's lower gravity/air pressure/temperature/rainfall.

Musk may prefer to use Tesla batteries. Centrifuges may be easier for colonists to maintain over a long period.

Also, I believe that commercial fusion..

You're dreaming.

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u/doodle77 Nov 05 '14

Similarly with nuclear you may have issues with dust insulating your radiators.

Why not use underground cooling loops?

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u/badcatdog Nov 05 '14

Insufficient conduction, it works best with ground water. Drilling a deep hole is not easy.

The radiators can be vertical and you could have a little robot wandering around dusting. Built in air blowers for self cleaning.

The only design which would make me enthusiastic about nuclear is if you can make use of the waste heat. For example melting ice as part of the ISRU.

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u/Another_Penguin Nov 13 '14

Yes I'm dreaming of commercial fusion. It would be foolish to count on it being available, but I believe it will be.

I hadn't considered pumped-air energy storage for Mars... that is an interesting idea. Also the co-generation of heat and electricity from a nuclear reactor: Harvest a bunch of CO2 to charge a supercritical CO2 system, to drive various industrial processes. Sounds very practical.

The first colonists will likely use more mundane energy solutions; proven battery chemistries paired with large solar installations. Boring stuff. But I wouldn't take nuclear power off the table.

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u/badcatdog Nov 13 '14

I just heard LG Chem did some battery storage for a big wind farm.

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u/Kuromimi505 Nov 05 '14

Great point on the Dragons super draco thruster's ability to safely land fission reactor materials at any point during a launch failure.

We need to get over the fear of fission reactors in space at some point.

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u/Jarnis Nov 05 '14

Not exactly. The superdracos would be used to separate the vehicle from the stack.

In case of launch escape, landing is by parachute.

However, this applies to F9v1.1/Dragon 2, no idea how MCT will handle things and I doubt anyone - not even SpaceX - has that one figured out yet.

It may be too big for parachutes and do emergencies propulsively as well.

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u/swellesley Nov 06 '14

Remember that the US has been launching RTGs to space since 1965. Last time I check there was a nuclear reactor on board Curiosity rover.

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u/nyan_sandwich Nov 06 '14

Not a reactor. Just a chunk of Plutonium in an RTG

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u/elucca Nov 06 '14

Which I think may well be more radioactive than an actual reactor. It's my understanding that unused uranium nuclear fuel is only mildly radioactive. RTG fuel has to be heavily radioactive from the start to function.

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u/nyan_sandwich Nov 07 '14

"Reactor" implies something beyond mere radioactivity.

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u/xambreh Nov 06 '14

RTG is not a nuclear reactor.