Space Based Solar Power For the Moon

[savuporo]

such schemes have been proposed before.

That a Lunar base should be powered by a multi-megaWatt SBSP station? I don't think so. But if you've got a reference, I'd love to see it.

just one most obvious example
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890017428_1989017428.pdf

Thanks savuporo. Very interesting paper, especially the discussion about apertures, etc. It also shows that lasers aren't a panacea because the conversion of electricity to laser light is less efficient than converting to microwaves.

This is just one of the classic papers by G. Landis, there is quite a bit more research around on this.
I suggest trawling NTRS and scholar.google.com. For a backgrounder, look here http://www.geoffreylandis.com/laser.htp

[Andrew_W]

The problem with both thermal solar and nuclear is cooling. There are rivers of running water you can use to cool down your steam. The only thing you could do, perhaps, is an underground system of piping that would cool things conductively, but now you're adding a whole other layer of mass and complexity.

I doubt the underground piping would work too well by itself as thermal conduction through rock and soil isn't that high, though maybe with just a little more complexity an underground cold store might work, with another set of piping to the surface that runs coolant only at night.

That SBSP is looking better and better.

[Warren Platts]

That SBSP is looking better and better.

It would be a 3 for 1 technology-wise: (1) it would provide plenty of power for a major Lunar ISRU station; (2) it would be the world's first practical SBSP system; (3) for the SEP folks, 20 megaWatts and 4 hectares of solar panels are probably a minimum that would be necessary for an SEP-powered, human-carrying MTV. RoboChris could probably correct me if I'm wrong about that.

Re: with the latter, thus the DDT&E costs for a major SEP system would largely be absorbed by the Lunar station costs.

[JohnFornaro]

I continue to favor concentrated solar power for use on the lunar surface.

Which is pretty much the proposal that I have left open for discussion on that Spudis and Lavoie thread.  There have been some suggestions that a Sitrling or maybe an Ericsson cycle engine might be prefereable as the prime mover, but there is not the body of knowledge on these heat engines that there is concerning steam turbines.

Steam turbines.  That's what you invest in.

[Warren Platts]

I continue to favor concentrated solar power for use on the lunar surface.

Which is pretty much the proposal that I have left open for discussion on that Spudis and Lavoie thread.  There have been some suggestions that a Sitrling or maybe an Ericsson cycle engine might be prefereable as the prime mover, but there is not the body of knowledge on these heat engines that there is concerning steam turbines.

Steam turbines.  That's what you invest in.

Only one problem: how do you cool your steam once you recover it?

[gbaikie]

In this case nuclear power is clear a better power source.

Why?

I just explain from a reliability perspective.  I do not see how space based solar power using satellites can be nearly as reliable as nuclear reactors on the surface. 

On top of that satellites are probably one of the few things more expensive than nuclear power.

I continue to favor concentrated solar power for use on the lunar surface. 

http://en.wikipedia.org/wiki/Concentrated_solar_power

Concentrated solar power (CSP) systems, are systems that use mirrors or lenses to concentrate a large area of sunlight, or solar thermal energy, onto a small area. Electrical power is produced when the concentrated light is converted to heat which drives a heat engine (usually a steam turbine) connected to an electrical power generator.

Concentrate the sunlight with mirrors fabricated from Mylar - perhaps even via inflatable heliostats.

Hmmmm . . .

I wonder if an inflatable heliostat could be made to turn and track the sun via selective inflation and deflation?

The launch mass of such a system would seem far less than either nuclear or photovoltaic.

Focusing on reflectors, has it's merits. It seems rather silly not to use any reflectors. One can use reflector to merely increase the electrical output of solar panels. One could use them to simply provide light in a dark crater. For days the sun stays in one spot in the sky- and so it's a lot different than on earth. But perhaps having the ability of having reflector which are mobile- and how they can be moved should be considered. All kinds of things are possible, hanging them from wires, rail tracks, rocket powered, or wheeled.

[Warren Platts]

It seems rather silly not to use any reflectors. For days the sun stays in one spot in the sky-

No.... The sun apparently moves ~13 degrees every (Earth) day.

[DarkenedOne]

You can bring up a reactor the size of a trash can, and set it up on the lunar surface.

Altho this is the most simple conceptual plan for lunar power that I've ever heard, it will not happen, because there are no plans whatsoever, unless in some skunk works somewhere, to make such a "nuclear battery".  However, as some wag pointed out to me in a very helpful fashion:  It's a free country, go ahead and build one.

Nasa was developing one when they were preparing to go to the moon for Constellation.

[DarkenedOne]

The problem with both thermal solar and nuclear is cooling. There are rivers of running water you can use to cool down your steam. The only thing you could do, perhaps, is an underground system of piping that would cool things conductively, but now you're adding a whole other layer of mass and complexity.

On the moon you have the moon itself as a thermal mass.  Or you can just radiate it out into space like NASA wanted too. http://www.engadget.com/2008/09/11/nasa-looking-to-go-nuclear-on-the-moon/

[JohnFornaro]

Steam turbines.  That's what you invest in.

Only one problem: how do you cool your steam once you recover it?

Now you're just being polite.  There's actually many problems to solve in this dozen F9 launch scheme I've cooked up.  Cooling the steam is one of them, for sure.  I've considered piping the hot water back into the crater for use in melting.  But I've been stuck at the Stirling engine analysis for a month or two.  Lately, I've been reading up on steam.  Great stuff, largely because of the body of practical experience in steam turbines, when compared to the body of practical experience in Stirling engines.  And, if the initial estimates are correct, there's plenty of water to make steam with up there.

To Darkened One:  I'm sure NASA was developing a nuclear battery.  Are you just pointing this out as a general observation?

[DarkenedOne]

Steam turbines.  That's what you invest in.

Only one problem: how do you cool your steam once you recover it?

Now you're just being polite.  There's actually many problems to solve in this dozen F9 launch scheme I've cooked up.  Cooling the steam is one of them, for sure.  I've considered piping the hot water back into the crater for use in melting.  But I've been stuck at the Stirling engine analysis for a month or two.  Lately, I've been reading up on steam.  Great stuff, largely because of the body of practical experience in steam turbines, when compared to the body of practical experience in Stirling engines.  And, if the initial estimates are correct, there's plenty of water to make steam with up there.

To Darkened One:  I'm sure NASA was developing a nuclear battery.  Are you just pointing this out as a general observation?

Nuclear battery is typically reserved for radioisotope generators.  What NASA was planning on developing was a full-fledged, self-contained reactor that could generate many kilowatts of power with minimal setup. 

[Warren Platts]

The problem with both thermal solar and nuclear is cooling. There are rivers of running water you can use to cool down your steam. The only thing you could do, perhaps, is an underground system of piping that would cool things conductively, but now you're adding a whole other layer of mass and complexity.

On the moon you have the moon itself as a thermal mass.  Or you can just radiate it out into space like NASA wanted too. http://www.engadget.com/2008/09/11/nasa-looking-to-go-nuclear-on-the-moon/

It's not that simple. The link you provided describes a 40 kilowatt system--about 3 orders of magnitude less than what would be required for a major Lunar propellant operation. So you're trading hectares of PV panels for (probably more I'm guessing) hectares of radiative panels (which are going to be in the sunlight for much of the time).

Geothermal-in-reverse is no panacea either. The nuke plant will heat up the rock faster than the rock can lose the heat to surrounding rock. It will work at first, but eventually, you'll heat up the rock to the temperature of the steam. The longer you make your pipe system, the longer the reservoir will last, but now you're talking about bringing a fully fledged drilling operation capable of drilling thousands of feet (not to mention the thousands of feet of casing that would be required).

I think having such a drilling capability will be useful in the long run. My own calculations suggest that water could exist in a liquid phase at about 9 km down below the surface on average. Fractured basalt can actually make a decent reservoir rock (it's sometimes used to store natural gas on Earth). Who knows? Maybe there's even live organisms living down there in Lunar aquifers.

But the point is building up such a drilling capacity is going to take many 20-mT cargo flights (probably around 10 or 20 at a minimum judging from the land rigs I've been around).

It would be nice if you could drop a 20 megawatt nuke plant in a single cargo flight and have it work, but it looks to me the auxiliary equipment that would have to go along with it (massive radiative panels or massive drilling equipment) would require many more than a single cargo flight.

And it's the number of cargo flights that determine the economics of a 1st generation facility, which is after all what we're talking about.

Nuke plants might make sense for a second or third generation facility, especially if some steel making capability could be developed (so you could make your own drill pipe and casing). But for a first generation Lunar station, it's not at all clear that a nuke plant (or solar thermal) would be more economical than a PV system, whether in orbit or on the surface. 

[gbaikie]

The problem with both thermal solar and nuclear is cooling. There are rivers of running water you can use to cool down your steam. The only thing you could do, perhaps, is an underground system of piping that would cool things conductively, but now you're adding a whole other layer of mass and complexity.

On the moon you have the moon itself as a thermal mass.  Or you can just radiate it out into space like NASA wanted too. http://www.engadget.com/2008/09/11/nasa-looking-to-go-nuclear-on-the-moon/

It's not that simple. The link you provided describes a 40 kilowatt system--about 3 orders of magnitude less than what would be required for a major Lunar propellant operation. So you're trading hectares of PV panels for (probably more I'm guessing) hectares of radiative panels (which are going to be in the sunlight for much of the time).

I think think system that provide 40 kilowatts is adequate for lunar mining in the first 4-5 years. Though it wouldn't be a  major Lunar propellant operation. I don't see any need for lunar mining operation to begin with using large scale operation.
The problem now and the problem then is the "shortage" of market.
I think we need to provide a market, and then grow the market.

If you want to "artificially" create a market- and you have govt or some really rich dude, there are ways of doing this which could be more effective [require less time and less money].

[DarkenedOne]

The problem with both thermal solar and nuclear is cooling. There are rivers of running water you can use to cool down your steam. The only thing you could do, perhaps, is an underground system of piping that would cool things conductively, but now you're adding a whole other layer of mass and complexity.

On the moon you have the moon itself as a thermal mass.  Or you can just radiate it out into space like NASA wanted too. http://www.engadget.com/2008/09/11/nasa-looking-to-go-nuclear-on-the-moon/

It's not that simple. The link you provided describes a 40 kilowatt system--about 3 orders of magnitude less than what would be required for a major Lunar propellant operation. So you're trading hectares of PV panels for (probably more I'm guessing) hectares of radiative panels (which are going to be in the sunlight for much of the time).

Geothermal-in-reverse is no panacea either. The nuke plant will heat up the rock faster than the rock can lose the heat to surrounding rock. It will work at first, but eventually, you'll heat up the rock to the temperature of the steam. The longer you make your pipe system, the longer the reservoir will last, but now you're talking about bringing a fully fledged drilling operation capable of drilling thousands of feet (not to mention the thousands of feet of casing that would be required).

I think having such a drilling capability will be useful in the long run. My own calculations suggest that water could exist in a liquid phase at about 9 km down below the surface on average. Fractured basalt can actually make a decent reservoir rock (it's sometimes used to store natural gas on Earth). Who knows? Maybe there's even live organisms living down there in Lunar aquifers.

But the point is building up such a drilling capacity is going to take many 20-mT cargo flights (probably around 10 or 20 at a minimum judging from the land rigs I've been around).

It would be nice if you could drop a 20 megawatt nuke plant in a single cargo flight and have it work, but it looks to me the auxiliary equipment that would have to go along with it (massive radiative panels or massive drilling equipment) would require many more than a single cargo flight.

And it's the number of cargo flights that determine the economics of a 1st generation facility, which is after all what we're talking about.

Nuke plants might make sense for a second or third generation facility, especially if some steel making capability could be developed (so you could make your own drill pipe and casing). But for a first generation Lunar station, it's not at all clear that a nuke plant (or solar thermal) would be more economical than a PV system, whether in orbit or on the surface. 

Wait first of all lets talk about the power required.  Where do you get the megawatt figure.  As with most things it would be wise to start out small than grow.  An operation with a few tens of kilowatts is more than enough IMHO to get things started. 

Secondly lets talk about the power usage.  Radiators are only needed to convert the heat generated from the nuclear reactor into electricity.  A lunar propellant operation would require heat probably more than any other form of energy.  Heat to keep machines and humans warm, to melt lunar ice, and heat for use in high temp electrolysis. 

Thirdly lets talk about ISRU.  Solar panels are require advanced technology, expensive facilities, and expensive materials to manufacture like other semiconductor technology.  Pipes and radiators on the other hand are a simple technology that requires cheap facilities to manufacture, and can be constructed from cheap, abundant materials.  In fact I would not even both with producing anything.  I would just use a tunnel boring machine like the ones used to run pipes, and cement the sides.

4.  The nuclear reactors on subs are trash canned size and deliver tens of megawatts of power.  The limitation is not so much the reactor itself, but the process of generating electricity.

 

[Patchouli]

I continue to favor concentrated solar power for use on the lunar surface.

Which is pretty much the proposal that I have left open for discussion on that Spudis and Lavoie thread.  There have been some suggestions that a Sitrling or maybe an Ericsson cycle engine might be prefereable as the prime mover, but there is not the body of knowledge on these heat engines that there is concerning steam turbines.

Steam turbines.  That's what you invest in.

Only one problem: how do you cool your steam once you recover it?

I would not use water as the working fluid instead I'd go with a molten salt reactor design and a Brayton cycle turbine with gaseous a helium loop.

Even if water was the primary coolant I still would go with a MSR design.

It would be best to have multiple power sources as each has it's own strength and weakness.
Solar wins hands down during the lunar day but during the lunar night nuclear is by far the best option.

If I designed a lunar base it would use solar during the day and at night since the thermal environment is better the reactor would throttle up and be the primary energy source.

As for beamed power it's probably not going to happen anytime soon due to the masses involved and conversion efficiencies.
I certainly would not want it on the critical path.

[Andrew_W]

I would not use water as the working fluid instead I'd go with a molten salt reactor design and a Brayton cycle turbine with gaseous a helium loop.

Even if water was the primary coolant I still would go with a MSR design.

It would be best to have multiple power sources as each has it's own strength and weakness.
Solar wins hands down during the lunar day but during the lunar night nuclear is by far the best option.

If I designed a lunar base it would use solar during the day and at night since the thermal environment is better the reactor would throttle up and be the primary energy source.

As for beamed power it's probably not going to happen anytime soon.
I certainly would not want it on the critical path.

So you're choosing the cost and complexity of two systems over one.

Even looking at just the L1 SPS vs surface based power, I don't see any reason to think surface is cheaper, it'll require an extra 2.4 km/s to land it, it'll need to be structurally stronger (heavier) for working in a gravity field and turning to track the sun. The surface based rectenna, which is the only bit of a L1 power system needed on the Moon, would be very light.

Certainly an L1 SPS system isn't useful until you get to a multi-MW demand, but once there I don't think either surface solar or nuclear could be competitive, having to use both? Nope.

Edit: Thinking about it some more, the area of the rectenna if using microwaves is going to be substantial, so its mass could be considerable if its mass/area isn't very low.

[Proponent]

Wait first of all lets talk about the power required.  Where do you get the megawatt figure.  As with most things it would be wise to start out small than grow.  An operation with a few tens of kilowatts is more than enough IMHO to get things started.

I'm inclined to agree; Spudis & Lavoie envision producing about a tonne of propellant per year per kilowatt of electrical power.

Secondly lets talk about the power usage.  Radiators are only needed to convert the heat generated from the nuclear reactor into electricity.  A lunar propellant operation would require heat probably more than any other form of energy.  Heat to keep machines and humans warm, to melt lunar ice, and heat for use in high temp electrolysis.

Lunar soil is a poor conductor of heat.  Given that the equipment and people, if any, will be surrounded by lunar soil and vacuum, I doubt that keeping them warm will figure prominently in the energy budget.  If it does, we're doing something wrong.

Thirdly lets talk about ISRU.  Solar panels are require advanced technology, expensive facilities, and expensive materials to manufacture like other semiconductor technology.  Pipes and radiators on the other hand are a simple technology that requires cheap facilities to manufacture, and can be constructed from cheap, abundant materials.  In fact I would not even both with producing anything.  I would just use a tunnel boring machine like the ones used to run pipes, and cement the sides.

Surely for power production on the order of just 100 kW there's little point in developing in situ manufacturing of any kind.  Just ship the power plant from earth.  Besides, the low conductivity of lunar soil makes cooling pipes difficult.  Methinks we're looking at radiators if we want either nuclear power (as NASA proposed) or high-temperature electrolysis.

[JohnFornaro]

I would not use water as the working fluid instead I'd go with a molten salt reactor design and a Brayton cycle turbine with gaseous a helium loop.

Maybe that would be the theoretical best thing.  But the salt and the helium are not up there already; water is abundant.  My line of thinking is to use what resources are available. I had no idea what the efficiencies might be, so I took a quick look at Moran & Shapiro "Fundamentals of Engineering Thermodynamics".

The first thing I noticed is the additional complexity required by the addition of a compressor in front of input heat exchanger, run off of the turbine axle as is done in jet engines and similar gas turbines.  According to Moran & all, "a relatively large portion of the work developed by the turbine is required to drive the compressor".  The Brayton cycle works best, that is, its thermal efficiency increases when there is an "increasing pressure ratio across the compressor".  This is related to temperature as well, but there is an upper limit of about 3060 degrees R on the turbine inlet, due to metallurgical limitations.  There are theoretical gains in efficiency which cannot be made due to this limitation.  Further, the cycle is such that the trade is mass flow for power output, and mass flow requires, well, more mass, in the prime mover, but I don't know how that compares to masses for a steam turbine of similar power output.  I studied some of the example problems, but couldn't get a good handle on efficiencies in five minutes.

In short, a closed Brayton cycle looks to be an appropriate type of prime mover for power generation on the Moon, with a solar heat input.  My limited analysis relies on the simplicity of a steam based vapor system, and the ready local availability of a working fluid.

Even looking at just the L1 SPS vs surface based power, I don't see any reason to think surface is cheaper, it'll require an extra 2.4 km/s to land it, it'll need to be structurally stronger (heavier) for working in a gravity field and turning to track the sun.

As always, I'm less concerned about the 2.4km/s.  The trade I'm seeing is a lunar base of the same population no matter the power system.  If people aren't landing and taking off, and prop isn't being shipped to the depot, the choice of power systems becomes far less important.  The way I'm seeing a polar parabolic mirror array, or a polar linear PV panel array working, is that the focal axis of the array, aligned with the sun, rotates round its vertical axis at the leisurely rate of one r per lunar day.  Some power would have to be drained from the system to drive the rotation mechanism, and structural mass would be required to support the rotation mechanism, and all of this would have to be landed on the surface and assembled.

I would say that the assembly of the surface structure would be easier than the zero gee assembly of the space structure of similar net power output.  By "net power output", I mean the power at the plug, available for the base or the cracking plant, or whatever, assuming either system is fully implemented.  Obviously, the rectenna and its associated power conversion mechanism would have to be landed at 2.4km/sec.  Without a more detailed design, I couldn't comment on which one would be cheaper.

One system which I briefly considered would be a constellation of six power sats in a heliocentric polar orbit, which transter power between themselves such that the sat which is over the trackable rectenna is always beaming power to the base/plant.  That's a fair amount of complexity when compared to a rotating parabolic mirror.  Another system would be a heliocentric power sat at L1 or L2, beaming power to a perpendicular rectenna at the poles, which would have to rotate around its vertical axis in the same fashion as the rotating parabolic mirror.  Either of these systems is not readily characterized as "cheaper" than a ground based parabolic mirror or PV array, without a good bit more detail.

I'm pretty sure that cooling would have to be radiative, from an area of perpetual shadow.  The scheme I've been cooking up would feature a large circular area in perpetual shadow, which eventually would cool down to a chilly temperature, and be the home of the cooling fins.  I haven't yet calculated the size of this thing however.

Pesky detail.

[Warren Platts]

Edit: Thinking about it some more, the area of the rectenna if using microwaves is going to be substantial, so its mass could be considerable if its mass/area isn't very low.

From the formula from the savuporo link, Diameter of rectenna = 0.61 * d * wavelength. If highest frequency microwave is used, (wavelength = 1mm), and assuming 60,000,000 m from L-points, then your're looking at a rectenna with a 36 km diameter: much larger than Whipple Crater itself (~10 km).

Clearly, we want to go with lasers. For a wavelenth of 2*10^-7 m, then the receiver would only be the size of about 10 meter diameter.

[Bill White]

Supercritical CO2?

The density of the material allows much smaller turbine blades, which need to be shipped from Earth in any event.

Also, the Moon has abundant O2 and the C can shipped as fuel and run through an ordinary generator to produce electricity and CO2 as a by product.

Sandia Labs News Releases

March 4, 2011
Supercritical carbon dioxide Brayton Cycle turbines promise giant leap in thermal-to-electric conversion efficiency

ALBUQUERQUE, N.M. — Sandia National Laboratories researchers are moving into the demonstration phase of a novel gas turbine system for power generation, with the promise that thermal-to-electric conversion efficiency will be increased to as much as 50 percent — an improvement of 50 percent for nuclear power stations equipped with steam turbines, or a 40 percent improvement for simple gas turbines. The system is also very compact, meaning that capital costs would be relatively low.

https://share.sandia.gov/news/resources/news_releases/brayton-cycle-turbines/

and this

Research focuses on supercritical carbon dioxide (S-CO2) Brayton-cycle turbines, which typically would be used for bulk thermal and nuclear generation of electricity, including next-generation power reactors. The goal is eventually to replace steam-driven Rankine cycle turbines, which have lower efficiency, are corrosive at high temperature and occupy 30 times as much space because of the need for very large turbines and condensers to dispose of excess steam. The Brayton cycle could yield 20 megawatts of electricity from a package with a volume as small as four cubic meters.

http://www.physorg.com/news/2011-03-supercritical-carbon-dioxide-brayton-turbines.html

= = =

Also too, supercritical CO2 handling capability will allow astronauts to clean their clothing without water and clean clothes will improve morale.

Seriously . . .

Cleaning with supercritical carbon dioxide