Space Based Solar Power For the Moon

[Warren Platts]

A variation on the traditional concepts of SBSP occurred to me the other day. Ordinarily, we envision a big array in GEO that beams to a fixed spot on the Earth. Alternatively, some people envision a solar station built on the Lunar surface out of Lunar materials that would beam energy back to Earth.

What I propose is that we reverse the direction of power: set up the solar PV array at an Earth-Moon Lagrange point, and then beam the energy to the Moon in order to power a Lunar research/propellant station.

The motivation is that producing respectable amounts of Lunar propellant is supremely energy intensive: e.g., to produce a mere 10,000 mT of ISRU propellant per year, it would probably require on the order of 20 megaWatts to get this done. Such an array would rival the largest PV arrays that have been built right here on Earth. It would be heavy and would require numerous landings to the surface of the Moon. In addition, building the array in a zone of perpetual sunshine isn't really much help because the angle of the sun is so low, the solar panels will wind up shading each other. The power requirements are probably the closest thing to a true showstopper when it comes to Lunar ISRU.

The relatively NSSO study on SBSP makes the case that relatively small arrays might be economically worthwhile for certain applications like beaming power to a remote army Forward Operating Base where supply lines are thin. The idea is to focus the 1st-generation SPSB station on a place with high strategic value where energy costs are already at least an order of magnitude more expensive than normal electrical costs.

Well, a Lunar station would fit that bill nicely. The research station would have a strategic value to the US, and it's electricity requirements would be very expensive.

So it might make sense (be cheaper) to build a 20 megaWatt array at a Lagrange point, and then beam the energy (microwaves or laser?) to the Lunar station.

Pros:
24-7 sunlight
lighter weight
much reduced launch costs

Cons:
have to build rectenna on Moon
this is possibly complicated by locating base at polar latitudes

What do you guys think?

[savuporo]

such schemes have been proposed before.
a really simple variant of which would be using a regular solar powered rover in permanently shadowed lunar craters, by illuminating its panels from lunar orbit with a laser.

[Warren Platts]

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.

[Hop_David]

A variation on the traditional concepts of SBSP occurred to me the other day. Ordinarily, we envision a big array in GEO that beams to a fixed spot on the Earth.

One of the problems with GEO SBSP to earth's surface is the 36,000 km distance. You need large rectenna receiving stations as well as large satellites.

What I propose is that we reverse the direction of power: set up the solar PV array at an Earth-Moon Lagrange point,

EML1 and 2 are nearly twice as far from the moon's surface than GEO is from earth's surface. EML4 and 5 about ten times as far.

For these you would need even bigger rectennas and space power sats.

Establishing large rectennas on the moon would also require a daunting amount of upmass.

[Warren Platts]

A variation on the traditional concepts of SBSP occurred to me the other day. Ordinarily, we envision a big array in GEO that beams to a fixed spot on the Earth.

One of the problems with GEO SBSP to earth's surface is the 36,000 km distance. You need large rectenna receiving stations as well as large satellites.

What I propose is that we reverse the direction of power: set up the solar PV array at an Earth-Moon Lagrange point,

EML1 and 2 are nearly twice as far from the moon's surface than GEO is from earth's surface. EML4 and 5 about ten times as far.

For these you would need even bigger rectennas and space power sats.

Establishing large rectennas on the moon would also require a daunting amount of upmass.

I just found an interesting paper that proposes a hybrid laser-microwave SBSP system to provide emergency power for disaster relief or military FOB's. They would broadcast power to a blimp or something in the stratosphere (~20 km up) using a laser, which would then rebroadcast microwaves to a portable rectenna on the Earth's surface.

The thing is, the reason microwaves are chosen is because they're more or less unaffected by the Earth's weather; the problem with higher frequency implementations is that they get eaten up by atmosphere, and especially raindrops. Microwaves can work in all weathers.

Since there's no weather on the Moon, there's no need for microwaves and big rectennas. Just using lasers should hopefully result in beam spot sizes that would be manageable.

As for L4 and L5, I guess I was under the mistaken impression they were about the same distance as L2. No matter, for a Whipple Crater base, since it's a little on the Dark Side, the SBSP station would have to be @ L2.

http://ursigass2011.org/abstracts/ursi/CHGBDJK-3.pdf

[Andrew_W]

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.

http://www.nss.org/settlement/ColoniesInSpace/colonies_chap06.html

The colony will earn its economic keep by building power satellites. The first of these will be maneuvered toward the moon. Forty thousand miles above the near side, it will be stabilized in position, its power beam directed to the lunar base. There, solar power will at last replace nuclear power.

Nuclear plants will serve for the early years of the lunar base as a ready source of power. But it is no more desirable to rely on nuclear power for the long run upon the moon than upon the earth. Just as on the earth, solar power from a satellite will be the long-term supply which ensures the permanence of the lunar base.

Prior to the arrival of the power satellite, the moon-miners will prepare for it. They will build large trough-shaped reflectors of aluminum to concentrate and gather the microwaves to be beamed from space. Possibly they will build a small aluminum plant there to meet the needs of the lunar base and render themselves that much less dependent upon the earth.

[DarkenedOne]

I think it would be many times more complex, more expensive, and significantly less reliable than simply using nuclear power as NASA was planning to do for its moon bases.

You can bring up a reactor the size of a trash can, and set it up on the lunar surface.  It would be able to provide many megawatts constantly for decades.

[DarkenedOne]

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.

http://www.nss.org/settlement/ColoniesInSpace/colonies_chap06.html

The colony will earn its economic keep by building power satellites. The first of these will be maneuvered toward the moon. Forty thousand miles above the near side, it will be stabilized in position, its power beam directed to the lunar base. There, solar power will at last replace nuclear power.

Nuclear plants will serve for the early years of the lunar base as a ready source of power. But it is no more desirable to rely on nuclear power for the long run upon the moon than upon the earth. Just as on the earth, solar power from a satellite will be the long-term supply which ensures the permanence of the lunar base.

Prior to the arrival of the power satellite, the moon-miners will prepare for it. They will build large trough-shaped reflectors of aluminum to concentrate and gather the microwaves to be beamed from space. Possibly they will build a small aluminum plant there to meet the needs of the lunar base and render themselves that much less dependent upon the earth.

". But it is no more desirable to rely on nuclear power for the long run upon the moon than upon the earth."

Sounds like typical anti-nuclear propaganda to me.  Nuclear power is ideal for outer space as there are practically no environment to worry about. 

Reactors here on Earth have to be heavily shielded in order to protect the environment and people.  Since space is already highly radioactive ships and buildings have to have heavy radiation protection anyway.

Also one must consider the point that the moon has more uranium than Earth does.

[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

[Andrew_W]

". But it is no more desirable to rely on nuclear power for the long run upon the moon than upon the earth."

Sounds like typical anti-nuclear propaganda to me.  Nuclear power is ideal for outer space as there are practically no environment to worry about. 

Reactors here on Earth have to be heavily shielded in order to protect the environment and people.  Since space is already highly radioactive ships and buildings have to have heavy radiation protection anyway.

Also one must consider the point that the moon has more uranium than Earth does.

Sounds like a typical nuclear addicts rant to me 

But since you've brought up the all-things-nuclear-are-wonderful point of view*, how easy would it be to run a nuclear station on the moon during daylight hours? the lunar surface gets pretty hot when the sun's up, and large nuclear requires large heat sinks, on Earth of course we can just run a river through the plant or use evaporative cooling, on the Moon you're restricted to radiators, which are ok (only ok, still going to be a system with a lot of mass) at night, not so great during the day.

* I'm actually politically neutral in the nuclear vs other systems debate, to get anything done in space cost has to come first.

[DarkenedOne]

". But it is no more desirable to rely on nuclear power for the long run upon the moon than upon the earth."

Sounds like typical anti-nuclear propaganda to me.  Nuclear power is ideal for outer space as there are practically no environment to worry about. 

Reactors here on Earth have to be heavily shielded in order to protect the environment and people.  Since space is already highly radioactive ships and buildings have to have heavy radiation protection anyway.

Also one must consider the point that the moon has more uranium than Earth does.

Sounds like a typical nuclear addicts rant to me 

But since you've brought up the all-things-nuclear-are-wonderful point of view*, how easy would it be to run a nuclear station on the moon during daylight hours? the lunar surface gets pretty hot when the sun's up, and large nuclear requires large heat sinks, on Earth of course we can just run a river through the plant or use evaporative cooling, on the Moon you're restricted to radiators, which are ok (only ok, still going to be a system with a lot of mass) at night, not so great during the day.

* I'm actually politically neutral in the nuclear vs other systems debate, to get anything done in space cost has to come first.

"nuclear addicts"

Now that is an interesting term.  You find plenty of people who are against nuclear, but how many people who tolerate nuclear power are against things like wind. 

I am for the best power source whatever that may be.  In this case nuclear power is clear a better power source.  On Earth power failures are tolerable, but in space a prolonged power failure results in life support failure, which results in death.   Satellites of course are exposed to all sorts of threats including attack by enemies, micrometeriods, radiation bursts, and etc.  A nuclear plant would be by comparison far less vulnerable.

[Andrew_W]

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

Why?

[gbaikie]

A variation on the traditional concepts of SBSP occurred to me the other day. Ordinarily, we envision a big array in GEO that beams to a fixed spot on the Earth. Alternatively, some people envision a solar station built on the Lunar surface out of Lunar materials that would beam energy back to Earth.

What I propose is that we reverse the direction of power: set up the solar PV array at an Earth-Moon Lagrange point, and then beam the energy to the Moon in order to power a Lunar research/propellant station.

The motivation is that producing respectable amounts of Lunar propellant is supremely energy intensive: e.g., to produce a mere 10,000 mT of ISRU propellant per year, it would probably require on the order of 20 megaWatts to get this done. Such an array would rival the largest PV arrays that have been built right here on Earth. It would be heavy and would require numerous landings to the surface of the Moon. In addition, building the array in a zone of perpetual sunshine isn't really much help because the angle of the sun is so low, the solar panels will wind up shading each other. The power requirements are probably the closest thing to a true showstopper when it comes to Lunar ISRU.

Mere 10,000 tonnes per year?
Anyhow, on the Moon, you put solar panel vertically. Particularly if one is talking about a large array. You want to put vertically because you would get higher percentage of sunlight.
And you could rotate the tower or panels on tower.
So, as guess if you want power in the range of 10 to 20 megawatt range, one might have tower heights of 1000' feet.
Whereas for more modest power needs the towers might 100' or less.

So it might make sense (be cheaper) to build a 20 megaWatt array at a Lagrange point, and then beam the energy (microwaves or laser?) to the Lunar station.

Pros:
24-7 sunlight
lighter weight
much reduced launch costs

Cons:
have to build rectenna on Moon
this is possibly complicated by locating base at polar latitudes

What do you guys think?

Or send power from earth to L-1 and bounce it to Moon.


The L-points are single point but are also a very large area/volume- and therefore if one has rectenna or whatever not at the point but instead region to the north or south of that point one could be able to send a signal to either the northern or southern lunar polar region.
Also I believe the point of L-1 is somewhere around 75,000 km from the Moon. But again the region of L-1 [or any L-point] is very large- and therefore one could still be in L-1 and be a lot closer to the Moon. Maybe say 30,000 km from the Moon. And/or by using delta-v [equal or similar as is used station keeping for LEO or GEO] one could probably get closer than 30,000 km.

Something related to what I am saying:
"For lunar communications and navigation, Ely recommends spacing three satellites 120º apart in the same elliptical orbit at an inclination of 51º. Each satellite in turn would go screaming down past periapsis (closest approach to the lunar surface) only 450 miles (700 km) above the north lunar pole, but would each linger fully 8 hours of its 12-hour orbit at 5,000 miles (8,000 km) above the horizon over the south lunar pole. In this configuration, two of the three satellites would always be in radio line-of-sight from a South Pole moonbase."
http://science.nasa.gov/science-news/science-at-nasa/2006/30nov_highorbit/
If rather than be 8000 km one could go even higher, say twice as high or say 20,000 km. Whether you dive toward the moon, or drift towards L-1 or L-2- the point is you spend a lot time sort of loitering directly above a pole [your orbital speed is very slow that far from the Moon. And/or said differently, according to above ref, you can't even have stable lunar above 750 km above the Moon- one certainly can't have a stable orbit 20,000 km away from the Moon

[MP99]

Anyhow, on the Moon, you put solar panel vertically. Particularly if one is talking about a large array. You want to put vertically because you would get higher percentage of sunlight.
And you could rotate the tower or panels on tower.
So, as guess if you want power in the range of 10 to 20 megawatt range, one might have tower heights of 1000' feet.
Whereas for more modest power needs the towers might 100' or less.

Those guys looking for perpetual sunlight locations on the Moon's surface had it all wrong. Build a tall enough tower and everywhere at the poles can get perpetual sunlight!

cheers, Martin

[MP99]

such schemes have been proposed before.
a really simple variant of which would be using a regular solar powered rover in permanently shadowed lunar craters, by illuminating its panels from lunar orbit with a laser.

The point here is to collect ice from the permanently-shadowed Lunar craters. These craters are the coldest places in the solar system, so they're getting less than Pluto's surface, ie <1/1500th the Moon's normal insolation. This is necessary for the ice to accumulate.

You laser is obviously intended to be more intense than normal sunlight. If the beam happens to traverse the crater by accident, what will happen to the ice in those craters that you'd been hoping to harvest?

Suspect same goes for microwave beams.

cheers, Martin

[DarkenedOne]

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.

[JohnFornaro]

WRT the OP:

such schemes have been proposed before.

Point that thing the other way. 

This in response to a suggestion for SBSP, pointed at the Earth.  If yer gonna build one of these things, point it at the Moon, where power is needed, not at the Earth, where there is plenty of power available.

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.

[Bill White]

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.

[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.

[Warren Platts]

Also one must consider the point that the moon has more uranium than Earth does.

False.

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.

Solar panels have worked reliably in space for decades. Nuke plants have not. Reliability is not the issue. Cost and politics are. There were people like Michio Kaku protesting the Cassini launch because they thought that was too risky.

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.

Those guys looking for perpetual sunlight locations on the Moon's surface had it all wrong. Build a tall enough tower and everywhere at the poles can get perpetual sunlight!

cheers, Martin

Right, ideally, you'd want one big panel up on the mountaintop that could spin 360 degrees; thus no solar panels would shade each other. The problem is the size of the panel would be measured in hectares. For 20 megaWatts, assuming 35% efficiency, the panel would be 4 hectares in area: 200 meters on a side if it's square. Thankfully, there's no wind on the Moon to blow it over, but still that's a pretty stupendous construction feat.