Monday, December 20, 2010

Soonest Space Solar Power

Space Solar Power has a bad rap, caused predominately by advocates who can't separate the exciting long term vision from the short term facts. In his recent paper, Al Globus has tried to rectify this by investigating what can be done with demonstrated launch vehicles, solar collectors and power beaming (and without on-orbit assembly, manned outposts, lunar materials, etc). His conclusion is that it appears space solar power is now ready for niche markets, such as forward military bases, where the price of power can be as much as $1/kWh.

The low cost launch vehicle of choice is, of course, SpaceX's Falcon 9. High specific power solar collection is achieved using thin-film heliogyros as demonstrated by the Japanese Ikaros satellite. The power beaming technology is infrared laser with custom solar panel receivers, as demonstrated by LaserMotive in their win at the Space Elevator Games last year.

A minor improvement in Globus' architecture is apparent. The mass of the spacecraft was estimated based on the throw capability of the Falcon 9 to geostationary transfer orbit (GTO), presumably because a solar sail style flight is expected to circularize the orbit, and solar sails can't start from low earth orbit (LEO). This is an implicit trade over a solar electric style flight from LEO, which I'm guessing is intended to utilize the solar collector for double duty in order to avoid additional mass. I'm not sure this trade wins. Even with a SMART-1 performance thruster, starting from LEO places 7751kg in GEO, 3.2 tons more than the estimated mass in the paper. If a NEXT thruster is available, the improvement goes up to 5.2 tons. However, this improvement only doubles the performance of the system, perhaps halving the price of power at the meter, which still doesn't make it competitive with the grid.

The problem is scale. Globus should be commended for describing a space solar power system that is achievable with current technology and could even make a profit in some niche markets, but let's think just a little bit further ahead for a moment. LaserMotive continues to improve the performance of their laser power beaming systems, so the 8% efficiency suggested may soon be on-par with the often quoted 10% efficiency of microwave power transmission. The paper suggests that SpaceX could reduce their prices by a factor of 3.6 if one ordered 1000 launches, but this claim is a few years old now. A more recent claim by SpaceX is that a super heavy lift vehicle could be built that delivers 130t to LEO for $300M per flight, a factor of just 2.3 - but the improved logistics of a single launch may offset that.

It should come as no surprise that reducing launch costs makes space solar power more feasible. What does surprise me is that sufficient specific power improvements in solar collection has been demonstrated which makes it reasonable to choose a lower efficiency beaming technique, with the resulting effect on the mass of the spacecraft making it launchable on existing boosters. This is a revolutionary idea which not only makes sense right now but defines a path for future work that will bring space solar power to the meter.


  1. Victor Moraes6:53 PM

    Sounds good, Trent. But not much. A system that alone is not able to raise from the ground, being only a second or third stage of a rocket strikes me more as a complication, without a substantial gain of power to lift cargo into space. It may cost less money, and the technology is already available in the market for an arrangement, but is still small. We need an innovation actually advantageous. Exit scheme jets, external combustion, for an internal combustion engine (or at least without external combustion), with mechanical drives. Sounds crazy, but NASA already has substance to do so. Indeed the use of a mechanical propulsion (something like helix wheel ...) into the vacuum, driven by an internal combustion engine or other rotary engines (electric - battery or solar or nuclear) can generate a huge potential to increase loads, as well as greatly reduce fuel consumption, extend the life of the spacecraft, enhance maneuverability, speed of travel, security. A revolution in concepts. NASA certainly do it, if you sense into his head, and not cling to old and inefficient to keep only the "industrial park" consolidated. You, Trent, heard about what I say. You even commented on Twitter that the U.S. Congress marked the period of one year to study a "machine" (I hope you remember what kind of machine I'm talking about), the normal way that would never need a "permission the Congress. " If it were a single machine, would require a year to study with the permission of Congress? If you do not remember what I say, I find some discreet way to explain to you. Trent friend a hug, and make sure that the solution will come, and I think, hopefully, will be propelled by mechanical (or physical) driven by motor-rotor internal combustion or without combustion.

  2. Victor, I appreciate your readership but I'd really prefer you put some more thought into your comments .. or just don't make them.

  3. Victor Moraes7:30 PM

    Ok! The thought is there, I did not detail. I thought you would appreciate the information.

  4. I don't think a military base would want to have a large infrared laser pointed at them.

    there's bound to be backscatter from the laser, no matter how good your solar panels are, making your power infrastructure an easy target for a (relatively simple) heat seeking missile... you're essentially laser painting yourself for the enemy's weapons.

    that said, I've often wondered whether 'space solar' factors in to Elon's plans - he's (large) part owner of Solar City, which is the biggest installer/manufacturer of solar panels in the US...

  5. Tony Rusi5:47 AM

    There are many short horizon innovations that are not mentioned here. Royce Jones's idea to reduce transmitter mass and rectenna mass by 90% by using sub-tundra orbits instead of GEO. Bill Manness's Idea of using a cloud of at least a 1000 smaller smartsats, and using solar ion drive to get from LEO to HEO. Then there are the new solar cells from Caltech and Stanford that should be 55% efficient and 98% plastic. Then there is the real killer cost reduction from using Sea Dragon Rockets instead of SpaceX Falcon XX's. Sea Dragons are $120 a pound to LEO, that's fifty times cheaper than SpaceX. Lastly there is the mass reduction benefit in using 5, 30, 60, or 90 GHz microwaves depending on weather conditions.

  6. Anonymous2:48 AM

    Thanks, Trent. Some good thoughts here.

    What is it about some posts that bring out the really wacko comments? First you've got Victor with some kind of magical device, then the obligatory comment by Gaetano, and lastly Tony quoting the launch price for a non-existent rocket! Wonders never cease...


  7. The human costs (on average 1 soldier or civilian is killed or wounded for every 24 convoys) is what's really pushing the US Military on this. Even if they dress it up for Congress and the MSM by noting this will help save on the ~$30/gal - ~$400/gal price at forward bases in the long run.

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  12. Anonymous7:14 AM

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