Power for a Mars colony

[savuporo]

After reading all this I am even more depressed.  Even if we can get to Mars in the next 15 years we won’t have any proven power for more than a handful of people.  If only a few percent of light gets through during a dust storms that last for a long time then solar can’t be counted on.

You have to remember that there have been multiple generations of solar powered manned space stations on orbit, and they have managed just fine, so there is no great cause for alarm : ) These stations on low earth orbit do not enjoy continuous sunlight either.

And, these space stations are fully dependent on everything trucked up from earth to expand or maintain its capabilities. A lunar or martian station, robotic or manned, will always have the advantage of utilizing local resources in some way to expand the capabilities. Power storage and power generation systems of various forms are high on the list.

[Burninate]

The challenge of ISRU is to harvest chemicals from Mars to build ~10 tons of fuel per ton of Earth-return mass, over the course of one or more ~2 year orbital conjunctions.  This is something that can be interrupted and resumed later.  A dust storm involves a decrease of solar flux by ~half, for a period of weeks.  This is not an insurmountable challenge.

[R7]

Geothermal energy might be practical in some regions.

[sghill]

The nuclear reactor (always specify: a safe several kilometers away from the base, where we don't have to care how radioactive it is) would be vastly favored were this Earth, because on Earth secondary cooling is a matter of phase-change of plentiful water into atmospheric water vapor, and convection of our thick mix of nitrox.  That is not the case in space - on the cooling side one generally requires large quantities of radiators, and this increases mass requirements & lowers efficiency substantially.  How much power one can *dump into* the Martian atmosphere and rock efficiently, using minimal mass and no maintenance, is still an open question.  There are varying degrees of problems translating the strategies we would use for this task on Earth, to Mars.

Why does it have to be far away? It can be exposed right at the surface and not affect anything.  Colonists are going to live in radiation hardened structures and wear suits outside anyway, the alpha and beta radiation from an unshielded reactor pales in comparison to the energy from a cosmic ray.

I don't see cooling as a huge problem either, once the colony takes the heat it wants from the reactor (a lot), the rest of the heat can be dumped and/or by moderating the fuel and turning the thing off.  The reactor can also dump any waste heat into ground heat exchangers for storage and slow release there- radiators don't have to be above ground. Likely they'd use any left over heat to release water from the soil, which will be a constant vital need at the colony.

A liquid salt reactor (see diagram) would be a good choice for a Mars application.  Actually, it'd be ideal: http://en.wikipedia.org/wiki/Molten_salt_reactor It's closed cycle uses the fuel as a cooling medium, and its preferable to keep the thing mighty hot, but it can be moderated far faster than a liquid reactor.  It's also orders of magnitude smaller and simpler in it's design- they made a few for aircraft in the 60's using iconel alloy for the non-fuel components (the same stuff SpaceX is 3D printing with for parts in the Super Draco)!  This type of reactor also doesn't go boom.  It just melts out (low pressure, high temps).  Plus it can be used as a breeder reactor, which is pretty much a given on Mars, as you'd want the ability to make more fuel or bombs there.  Lithium and thorium are likely

Consider this too, if water isn't a problem, rapid cooling can also occur by venting steam right out into the martian atmosphere.  The low pressure there means the phase change will be far more efficient than here on Earth.  I don't think this will be something they'll need on a regular basis, as they'll use all the power that thing can deliver, and moderate it down when they don't.

[A_M_Swallow]

Radiators can be made from metal or plastic.  Both are ISRU materials on Mars.

[jeffkruse]

I just read that Opportunity’s power dropped to 20% during a dust storm.  The same nasa article http://www.jpl.nasa.gov/news/news.php?release=2007-080  said that 99% of the light was blocked.  These storms lasted nearly a month.

99% of direct sunlight and 80% reduction in power I don’t quite get.  I thought power would be linear with the light.

An 80% reduction in power for months is survivable but 99% isn’t.  What would be the lowest % of power produced for the worst 1000 year dust storm?  If the power gets reduced to only 10% then that’s probably survivable,  But if it’s reduced to just a few % then you need backup power for possibly a long time.

Solar powered space stations don’t have dust storms that last for months. 

[R7]

excess heat to the greenhouses, thank you very much.

[sheltonjr]

I think nuclear is the way to go. Plenty of power and heat using only a 1.5 grams max of fuel per day. 1 KG will last 2 years. All fuel can come from Earth since the amount is so small.

A Molten Salt nuclear reactor was built in the 1950s that would be with some small modifications would be a good fit for a Mars colony providing 2.5 M Watts of heat and up to 1.25 M Watts of electricity. The reactor core is less than a meter tall and in diameter.  Weight would be about 5 Metric tons for the reactor and super critical CO2 power generation.

See my post here: http://forum.nasaspaceflight.com/index.php?topic=34413.msg1189731#msg1189731

A Molten Salt Reactor (MSR) is a very simple device. A pot, A pipe, A pump.

The reactor can be shipped to Mars cold. Never been run with nuclear fuel. It can be tested with clean molten salt.

Once on mars an excavator will dig a hole for it and bury it with the dual redundant pumps on top for easy replacement and the power turbine and heat pipes also accessible.

A few KW of power will be required to melt the salt and then fuel will be slowly added to bring the reactor critical. It is a load following reactor and no other controls will be needed. Just run the cooling pump for the turbine depending on how much electricity is needed.  Approximately 50 grams of fuel in solid molten salt form will be added monthly via a pipe from the surface to the fuel loop.

No heavy steel pressure vessel is required. The MSR is not pressurized and can run at Mars pressure or at most Earth pressure of 14 PSI. I believe Molten Fluoride Salt has low volatility at low pressure.

This reactor along with super critical CO2 turbines would not only be a good fit for Mars but the technology would useful for many applications on this planet as well.

[jeffkruse]

If these reactors are simple, safe, and reliable why don't we have any running now?  Being so simple and safe I would find it hard to believe they wouldn't be cost effective here on earth???

[savuporo]

If these reactors are simple, safe, and reliable why don't we have any running now?  Being so simple and safe I would find it hard to believe they wouldn't be cost effective here on earth???

I tried to point this out early in the thread. Due to the nature of nuclear ( well, fission ) technology, it will never really have commercial widespread use and remain heavily guarded domain of governments and military applications.

Ford Nucleon and Tu-119 never really exploded to the marketplace, so to speak.

[RanulfC]

I just read that Opportunity’s power dropped to 20% during a dust storm.  The same nasa article http://www.jpl.nasa.gov/news/news.php?release=2007-080  said that 99% of the light was blocked.  These storms lasted nearly a month.

99% of direct sunlight and 80% reduction in power I don’t quite get.  I thought power would be linear with the light.

An 80% reduction in power for months is survivable but 99% isn’t.  What would be the lowest % of power produced for the worst 1000 year dust storm?  If the power gets reduced to only 10% then that’s probably survivable,  But if it’s reduced to just a few % then you need backup power for possibly a long time.

Solar powered space stations don’t have dust storms that last for months.

"99%" vis "80%" question: Wavelength, the 1% that got through was part of the "wavelength" range the cells react well to. When they make the cells they can chart exactly how they react to various wavelengths and (specifically in the case of the Mars rovers) they select for optimum output under "x" conditions. Guess which these were "optimized" towards

The main reason they were so worried about the dust build up on the cells is because the dust as a coating simply blocked ALL wavelengths where as airborne dust still allows some bleed through.

"Tuning" cells allows them to get the high conversion efficeny ratings when "beaming" power with lasers. (As high as 95% in many lab tests, usually field testing never goes below 80%)

Randy

[Burninate]

Nothing so complicated.  99% of *direct* sunlight was the quote.  That means it absorbed most of its energy from light scattered by the dust & atmosphere.

Incidentally, this distinction, 'direct', only really matters for concentrating solar modes - those guys get absolutely screwed by scattering.  Traditional photovoltaics are fine.

[ncb1397]

After reading all this I am even more depressed.  Even if we can get to Mars in the next 15 years we won’t have any proven power for more than a handful of people.  If only a few percent of light gets through during a dust storms that last for a long time then solar can’t be counted on.
It has to be nuclear generators and they are not very simple to keep running.  All the other options like satellites transmitting power, Americium in RTG, etc are all still unproven.   

I wouldn't be depressed. Mars recieves about 184 exawatt-hours of power from the sun per earth-year. The land being currently unoccupied means that you could theoretically use all of it though the planet's moniker would need to be changed. Even collecting .1% @ 20% conversion efficiency would be about 1000x annual electricity production on earth.

[savuporo]

The land being currently unoccupied means that you could theoretically use all of it though the planet's moniker would need to be changed. ..

Exactly, the real estate will be cheap. You could blanket square miles of the ground with low efficiency silicon solar cells.

[Burninate]

The nuclear reactor (always specify: a safe several kilometers away from the base, where we don't have to care how radioactive it is) would be vastly favored were this Earth, because on Earth secondary cooling is a matter of phase-change of plentiful water into atmospheric water vapor, and convection of our thick mix of nitrox.  That is not the case in space - on the cooling side one generally requires large quantities of radiators, and this increases mass requirements & lowers efficiency substantially.  How much power one can *dump into* the Martian atmosphere and rock efficiently, using minimal mass and no maintenance, is still an open question.  There are varying degrees of problems translating the strategies we would use for this task on Earth, to Mars.

Why does it have to be far away? It can be exposed right at the surface and not affect anything.  Colonists are going to live in radiation hardened structures and wear suits outside anyway, the alpha and beta radiation from an unshielded reactor pales in comparison to the energy from a cosmic ray.

A completely unshielded, minimum-coolant-encased fission reactor of any substantial size outweighs solar & cosmic ray radiation by many orders of magnitude.  We keep them behind tons of concrete in addition to the containment dome for a reason.  Aside from normal operation, the prospects for a nuclear accident are substantial in a harsh unfamiliar environment, even if we suspect our design is passively safe on Earth.  The reactor being several kilometers downwind provides a safe buffer from even the worst meltdown / explosion / contamination risk, and is a cheap substitution for providing the traditional precautions against the worst case scenario, which we have the mass to do here on Earth.  On Mars, anything more complex to manufacture than structures an electric backhoe can make is inherently questionable.  I would like to see things like bricks produced, but I wouldn't bet colony success on it.

If something as simple as a wire reel and a rover body can remove radioactive contamination from the list of concerns, I'm all for it.

I don't see cooling as a huge problem either, once the colony takes the heat it wants from the reactor (a lot), the rest of the heat can be dumped and/or by moderating the fuel and turning the thing off.  The reactor can also dump any waste heat into ground heat exchangers for storage and slow release there- radiators don't have to be above ground. Likely they'd use any left over heat to release water from the soil, which will be a constant vital need at the colony.

A liquid salt reactor (see diagram) would be a good choice for a Mars application.  Actually, it'd be ideal: http://en.wikipedia.org/wiki/Molten_salt_reactor It's closed cycle uses the fuel as a cooling medium, and its preferable to keep the thing mighty hot, but it can be moderated far faster than a liquid reactor.  It's also orders of magnitude smaller and simpler in it's design- they made a few for aircraft in the 60's using iconel alloy for the non-fuel components (the same stuff SpaceX is 3D printing with for parts in the Super Draco)!  This type of reactor also doesn't go boom.  It just melts out (low pressure, high temps).  Plus it can be used as a breeder reactor, which is pretty much a given on Mars, as you'd want the ability to make more fuel or bombs there.  Lithium and thorium are likely

A breeder reactor is something we'd have to master on Earth before we could think about using it on Mars.  A U238-fueled breeder is something that would be immensely useful, but that we have not done successfully on a commercial basis yet.  Nuclear tech back when we were building reactors was every bit as hamstrung by conservatism and the lobbyists of interested parties as rocket launch tech was 10 years ago - with the difference that a lone billionaire is not sufficient to disrupt the nuclear industry.  *Hopefully* as we start to rev up the nuclear powerplant building corporate engines again, we'll opt for gen 4 designs exclusively - we should have been perfecting them for the last 30 years, once it became clear that gen 2/3 designs could fail catastrophically.  The fact that our U-235 stockpiles ran out, and we have to actually mine & refine the stuff again if we want to use it, should help.

Whatever the solution, we would likely require a design that can't melt down *or* fail to produce power in a way which is permanent without maintenance, needs no replacement cores (this is a feature of numerous small reactors, not just explicit breeders with distinct stages & purification rituals) and that requires few to no moving parts.

Consider this too, if water isn't a problem, rapid cooling can also occur by venting steam right out into the martian atmosphere.  The low pressure there means the phase change will be far more efficient than here on Earth.  I don't think this will be something they'll need on a regular basis, as they'll use all the power that thing can deliver, and moderate it down when they don't.

On Earth, once-through cooling systems are often considered wasteful, particularly by the cities downstream during droughts.  Gigawatt-scale plants actually burn through substantial portions of smaller rivers, emitting water vapor.  On Mars, water is for the most part *scarce*, no matter that it exists at some level, and best fed into as closed-loop a chemical workflow as possible.  Using it for once-through cooling implies mining it very rapidly.  I don't think this system has been examined adequately enough to make the assumption that it's easy, even at the polar caps.

[Burninate]

The land being currently unoccupied means that you could theoretically use all of it though the planet's moniker would need to be changed. ..

Exactly, the real estate will be cheap. You could blanket square miles of the ground with low efficiency silicon solar cells.

You could do it here too.  Real estate outside the urbanized areas of developed economies is, in fact, cheap, and the distribution infrastructure, while nobody wants to have to be the one to pay for it or file the permits, is so cheap to construct it's nearly free per unit of power*distance.   The limiting factor is not land, but solar panel cost.

[savuporo]

The limiting factor is not land, but solar panel cost.

I know, and we are past grid parity in many places of the world now. But thats off topic.

[Vultur]

I am not convinced solar is unworkable given how light thin films can be made -- dust storms can be dealt with by having more area of solar panel.

Thin films are used even on Earth so they are probably not THAT fragile, and they are light enough that you can bring extra to replace those torn in storms (also, wind speeds on Mars may be very high, but I believe the force is much less since the air is so thin).

I think the MERs' far-longer-than-expected lifetimes are a good argument that solar power is very workable at Mars and that dust conditions aren't as crippling as previously thought.

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It would also be useful to determine how much power a Mars colony would need. I would think insulation would be much more effective at reducing heating needs on Mars than in Antarctica -- surely Mars' much thinner atmosphere would be less effective at transporting heat away? Or is the difference not in fact that significant?

[aero]

I've been wondering how much power will be needed for Mars ISRU and the early stages of industrialization. Even 3-D printers use power after all, and making rocket fuel will take energy. How much? I think the answer is "a lot."

This is totally separate from the power needed to support the people and their food, clothing and shelter.

[R7]

dust storms can be dealt with by having more area of solar panel.

and by storing energy. Eventually you'll be cracking CO2/water anyway.