Solar Power Satellites

[Greg Hullender]

If Japan really decides to build one or more 10,000-ton solar power farms, that would provide business for lots of launches.

http://spectrum.ieee.org/green-tech/solar/how-japan-plans-to-build-an-orbital-solar-farm

The IEEE article includes lots of reasons why this may never get off the ground, of course, but it's interesting to think about what sort of economies of scale might be possible given projects like this. And what sort of projects might be possible given further reductions in price.

[Lar]

This article was mentioned already in the  SpaceX advances drive for Mars rocket via Raptor power thread

http://forum.nasaspaceflight.com/index.php?topic=34197.msg1192997#msg1192997 

Interested readers may want to review the post I referenced and some of the posts immediately after.

[TrevorMonty]

They have a long way to go to compete with terrestrial solar power but there some technologies in pipeline to make it more viable.

SpaceX BFR if it us fully reusable.
Tethers Unlimited SpiderFab.
Increasing Watts/ kg of solar panels.

Japan has talked about beaming power from moon to earth but actually sending power to lunar base from SSP satellite or even earth may be ideal for supplying power 24/7.

[cordwainer]

Unlike, Musk I think the conversion rates can be made efficient enough for this to be physically practical.  What makes it difficult is the initial cost in infrastructure which makes it non-competitive over other forms of power though. I think fusion research has a better chance in the short term of creating results than all the things that would have to come together to make space based solar power economical.

On a positive note you might be able to increase the efficiency of your microwave rectenna by using photonic crystals to tune the incoming microwaves for better absorption. You could also put your rectenna on a ground tethered high altitude dirigible to lower losses and prevent communication interference posed by beaming through the lower atmosphere.

[SICA Design]

On a positive note you might be able to increase the efficiency of your microwave rectenna by using photonic crystals to tune the incoming microwaves for better absorption. You could also put your rectenna on a ground tethered high altitude dirigible to lower losses and prevent communication interference posed by beaming through the lower atmosphere.

85% efficient rectennas (5.8GHz) have already been demonstrated in the lab. The way to improve further is to eliminate the schottky diode losses by using synchronous rectification and impedance matching for maximum power transfer.

Beam power losses through the atmosphere are less than 2% for 99% of all weather (including "very cloudy and severe rain" [Kantak, JPL, 2003]). Given that the rectenna needs to be at-least 4.5km across (for 5.8GHz) to meet the diffraction limit of a 1km satellite antenna located at GEO, I'm afraid the prospect of floating it is slim (and unnecessary).

5.8GHz is one of the ISM bands (industrial, scientific & medical), as-is 2.4GHz wi-fi. Interference is possible, but would be confined to the vicinity of the rectenna and the frequency band. Peak beam intensity for most proposals is kept below 300W/m2 (about 1/4 to 1/3 mid-day sun), a level safe for birds, bees and aircraft to fly through.

[Nomadd]

On a positive note you might be able to increase the efficiency of your microwave rectenna by using photonic crystals to tune the incoming microwaves for better absorption. You could also put your rectenna on a ground tethered high altitude dirigible to lower losses and prevent communication interference posed by beaming through the lower atmosphere.

85% efficient rectennas (5.8GHz) have already been demonstrated in the lab. The way to improve further is to eliminate the schottky diode losses by using synchronous rectification and impedance matching for maximum power transfer.

Beam power losses through the atmosphere are less than 2% for 99% of all weather (including "very cloudy and severe rain" [Kantak, JPL, 2003]). Given that the rectenna needs to be at-least 4.5km across (for 5.8GHz) to meet the diffraction limit of a 1km satellite antenna located at GEO, I'm afraid the prospect of floating it is slim (and unnecessary).

5.8GHz is one of the ISM bands (industrial, scientific & medical), as-is 2.4GHz wi-fi. Interference is possible, but would be confined to the vicinity of the rectenna and the frequency band. Peak beam intensity for most proposals is kept below 300W/m2 (about 1/4 to 1/3 mid-day sun), a level safe for birds, bees and aircraft to fly through.

85% efficient over what distance?

[SICA Design]

85% efficient over what distance?

Good question!

That is the efficiency for converting the incident beam power falling within the confines of the rectenna.

84% of the beam power is confined within a circular region called the "Airy disk" (George Biddell Airy), which dictates the minimum size of the rectenna and transmit antenna for a given frequency and beam path length. A larger rectenna would capture more of the beam, and could operate away from the equatorial band, e.g. a 12km rectenna could capture 88.5% of the beam power arriving at 20 degrees elevation, or 94.7% from directly overhead.

Other losses are at the satellite-end of the beam and include:

PV efficiency - 40% expected from multi-junction concentrated cells (44.7% demonstrated)
                    -  20% --> >50% expected from future thin-film (e.g. perovskite research, 19% demonstrated)
                    -  bear in-mind that earth-orbit solar flux is 57% greater than equatorial mid-day terrestrial sun, for 24/365.
PMAD (Power Management and Distribution)
                    - early (and some recent) proposals transport electrical power over multi-kilometre distances (from PV cells to microwave generators) and across rotating joints. Peter Glaser's (RIP 2014) original proposal required liquid helium-cooled superconductors.
                     - modern PMADs use "sandwich panel" concepts with distribution distances measured in cm
                     - overall conversion efficiency (electrical --> microwave) could achieve >70%

[floss]

Beaming power to earth is a pretty non starter (efficency of energy transfer) but using large solar plants to power antimater factories seems plausable .

Plus this would usher in the antimater era and give humanity the stars .

[mheney]

Beaming power to earth is a pretty non starter (efficency of energy transfer) but using large solar plants to power antimater factories seems plausable .

Plus this would usher in the antimater era and give humanity the stars .

I'm not sure you can say that transmission losses (a well-understood problem) makes a concept a non-starter, but then turn around and call antimatter factories is a plausible alternative...

[TrevorMonty]

Japan plan to test power beaming in next few years by fitting a transmitter to ISS. With 300kw on tap it makes a great test bed.

[floss]

Beaming power to earth is a pretty non starter (efficency of energy transfer) but using large solar plants to power antimater factories seems plausable .

Plus this would usher in the antimater era and give humanity the stars .

I'm not sure you can say that transmission losses (a well-understood problem) makes a concept a non-starter, but then turn around and call antimatter factories is a plausible alternative...

Just one alternative the fact is that every environmentalist will be up in arms and the building of anything that shoots death rays at earth will have a leagle minefield before it is built .
If the power is used to produce antimatter it would be of great benefit to humanity as a whole and the SSP need not be in Earth Orbit.
I know that initially Antimatter production would be brutally inefficent seeing as none has yet been built yet but we are talking about centuries of upgrades.

Producing power from off world is going to have massive startup costs and there is plenty of resorces on Earth humanity is only tapping the tip of the iceburg so far .

Plus the first Antimatter factory be a high risk effort and it would be handy to put it far away from Earth in case of accidents.

[Tass]

Beaming power to earth is a pretty non starter (efficency of energy transfer) but using large solar plants to power antimater factories seems plausable .

Plus this would usher in the antimater era and give humanity the stars .

I'm not sure you can say that transmission losses (a well-understood problem) makes a concept a non-starter, but then turn around and call antimatter factories is a plausible alternative...

Just one alternative the fact is that every environmentalist will be up in arms and the building of anything that shoots death rays at earth will have a leagle minefield before it is built .
If the power is used to produce antimatter it would be of great benefit to humanity as a whole and the SSP need not be in Earth Orbit.
I know that initially Antimatter production would be brutally inefficent seeing as none has yet been built yet but we are talking about centuries of upgrades.

Producing power from off world is going to have massive startup costs and there is plenty of resorces on Earth humanity is only tapping the tip of the iceburg so far .

Plus the first Antimatter factory be a high risk effort and it would be handy to put it far away from Earth in case of accidents.

Sending a ray down with the same intensity as sunlight, and which will defocus harmlessly if the pilot signal is interrupted, will have the environmentalists "up in arms", but shipping down packages of power which will explode like a nuke if containment fails, won't?

[floss]

Beaming power to earth is a pretty non starter (efficency of energy transfer) but using large solar plants to power antimater factories seems plausable .

Plus this would usher in the antimater era and give humanity the stars .

I'm not sure you can say that transmission losses (a well-understood problem) makes a concept a non-starter, but then turn around and call antimatter factories is a plausible alternative...

Just one alternative the fact is that every environmentalist will be up in arms and the building of anything that shoots death rays at earth will have a leagle minefield before it is built .
If the power is used to produce antimatter it would be of great benefit to humanity as a whole and the SSP need not be in Earth Orbit.
I know that initially Antimatter production would be brutally inefficent seeing as none has yet been built yet but we are talking about centuries of upgrades.

Producing power from off world is going to have massive startup costs and there is plenty of resorces on Earth humanity is only tapping the tip of the iceburg so far .

Plus the first Antimatter factory be a high risk effort and it would be handy to put it far away from Earth in case of accidents.

Sending a ray down with the same intensity as sunlight, and which will defocus harmlessly if the pilot signal is interrupted, will have the environmentalists "up in arms", but shipping down packages of power which will explode like a nuke if containment fails, won't?

Who said anything about shipping anything to Earth there is massive markets in space already .Next gen power systems for next gen jobs .(Terraforming Mars and Venus )
You will not get much power with just sunlights intensity and weather happens plus any rectenna will be out in the boonies so power will decrease rapidy .Unless superconducters are avalible which opens other cheaper alternatives.

[mheney]

According to the web site at http://www.daviddarling.info/encyclopedia/A/antimatterprop.html, current annual antimatter production at CERN and Fermilab (combined) is between 1- 10 nanograms/year.  Hardly an industrial process, and we don't have any facilities the size of CERN in orbit ....  Whereas microwave transmisson of power has been demonstrated many times already ...

And if you're talking about having massive markets in space, then there's your market for beamed power.  Point-to-point power transmission works very well in space.

Finally, if you want to talk environmentalist outrage (politely known as "regulatory issues"), then if you think microwaves is going to cause howling, just wait until you start talking antimatter in industrial quantities.   Because there's a bit of a difference in an accident with a microwave beam and an accident with antimatter.  I'll take the microwaves any day of the week, thank you very much.

Bottom line, dismissing a (technically) demonstrated technology because a speculative, non-existant technology would be superior is a non-starter.  See http://en.wikipedia.org/wiki/Unobtainium

[su27k]

Peak beam intensity for most proposals is kept below 300W/m2 (about 1/4 to 1/3 mid-day sun)

This may be a problem, think about it, if the power density is less than that of the sun, why not just use the sun light directly? Yes I know there're nights, weather issues with terrestrial solar power, but they seem to be much easier to solve than the problems facing SPS.

[bubbagret]

Peak beam intensity for most proposals is kept below 300W/m2 (about 1/4 to 1/3 mid-day sun)

This may be a problem, think about it, if the power density is less than that of the sun, why not just use the sun light directly? Yes I know there're nights, weather issues with terrestrial solar power, but they seem to be much easier to solve than the problems facing SPS.

Having the beam at 1 relatively narrow frequency band, even at a lower total areal power, would be considerably more efficient than trying to convert full spectrum sunlight in to usable power. Solar electric usually only converts very specific, narrow frequencies as does solar thermal. That would only be a small percentage of the total solar flux reaching the surface and then at conversion efficiencies that reduce that small percentage even further.

[Vultur]

Why does the beam intensity have to be so low? Couldn't you just not put the beams on airplane flight routes? Surely the occasional bird being cooked would be greatly outweighed by all the environmental damage from other forms of power that wouldn't be happening (I doubt it would even remotely be comparable to all the bird deaths from hitting skyscrapers and towers and things).

[SICA Design]

Why does the beam intensity have to be so low? Couldn't you just not put the beams on airplane flight routes? Surely the occasional bird being cooked would be greatly outweighed by all the environmental damage from other forms of power that wouldn't be happening (I doubt it would even remotely be comparable to all the bird deaths from hitting skyscrapers and towers and things).

There are two reasons:

1) There is already a large misplaced public perception that this would be a microwave "death ray", more dangerous than antimatter  . At least we have science on our side, giving a fundamental reason why that won't be the case:-

2) That fundamental reason is the diffraction limit; to halve the beam spot at the rectenna (and quadruple its intensity at the centre) requires doubling the diameter of the solar power satellite (SPS). To get the spot size down to 1 metre (where it could REALLY cause some sci-fi damage!) would require the satellite diameter (at GEO) to increase to 3,000km across.

For a geostationary SPS, the overall costs optimise for a design approximately 1km across and for power levels of 1GW or more. The reason we don't have one yet is due to launch costs, which Skylon and/or SpaceX FHR could address.

[Asteroza]

All the more reason why laser SPS has it's ups and downs. Small sizes are easier to demo overall. Tight spot size is great for reducing receiver area, but then it functionally approaches weapons grade beam densities rather quickly. Though I like to roll out that most space things are weapons already (most if not all satellites potentially can become kinetic impactor weapons from orbit).

The old SPS studies chose microwave because laser wasn't ready, and they chose the density to appeal to the average man who subjectively didn't relish the idea of being microwaved from orbit. As mentioned above, the physics says it needs to be 1Km or more for the transmitting antenna, at around 1GW based on those constraints. That fundamentally makes GEO demos hard. The japanese intend to do a LEO microwave demo as a proof-of-concept though, which is easier due to the distances involved at the expense of antenna tracking.

I have a personal belief (not necessarily backed with facts mind you) that laser (either laser thermal or hybrid laser PV/thermal) would be a better choice for the receiver architecture considering the process heat applications and not just electrical use. That, and it would enable a favorite pet idea, laser assisted Skylons.

[SICA Design]

All the more reason why laser SPS has it's ups and downs. Small sizes are easier to demo overall. Tight spot size is great for reducing receiver area, but then it functionally approaches weapons grade beam densities rather quickly. Though I like to roll out that most space things are weapons already (most if not all satellites potentially can become kinetic impactor weapons from orbit).

Very true!

The old SPS studies chose microwave because laser wasn't ready, and they chose the density to appeal to the average man who subjectively didn't relish the idea of being microwaved from orbit. As mentioned above, the physics says it needs to be 1Km or more for the transmitting antenna, at around 1GW based on those constraints. That fundamentally makes GEO demos hard. The japanese intend to do a LEO microwave demo as a proof-of-concept though, which is easier due to the distances involved at the expense of antenna tracking.

Microwaves between 1-10GHz were also chosen for their ability to pass through thick cloud and rain; the 5.8GHz ISM band is near optimal.

I have a concept for a 1 gigawatt SPS called HESPeruS - Highly Elliptical Solar Power Satellite - which traverses a Molniya orbit, a highly-elliptical orbit first used by the Russians. Like GEO, this is also a synchronous orbit, in-that the SPS loiters over the same two northern hemisphere locations alternately every 12 hours. There are several benefits:

* HESPeruS is of rigid construction, built from multiple hexagonal modules into an essentially flat structure capable of collecting sunlight and beaming to any latitude  above 45 degrees, without the complex rotating optics as needed for the 2nd Japanese option (and ALL GEO satellites).
* HESPeruS is complementary to GEO space solar power proposals, which suffer additional losses when beaming to high latitudes; 30% of Earth's ice-free land and a $7 trillion economy is located above 45 degrees latitude.
* It's 5.8GHz antenna is distributed over the full 4.4km diameter, with individual elements vacuum-spaced by <25mm, drawing power (10s of milliwatts) from local PV cells which point directly at the sun throughout the orbit - so negligible distribution losses.
* The large antenna to PV ratio means it can operate within the diffraction limit at one-tenth scale (100MW), meaning a pilot system can be launched at lower cost, and then expanded later (Molniya is a servicable orbit!).
* It costs less than half as much (principally propellant mass) to place a satellite on a Molniya orbit than it does to GEO.
* Just 3 HESPeruS satellites can supply 1GW continuous (24/365) power to two rectenna sites, such as the UK and Japan.

I have a personal belief (not necessarily backed with facts mind you) that laser (either laser thermal or hybrid laser PV/thermal) would be a better choice for the receiver architecture considering the process heat applications and not just electrical use. That, and it would enable a favorite pet idea, laser assisted Skylons.

That's Keith Henson's idea (he comments here) - hopefully his paper will be published around the same time as mine!

(Edited for typos)