|SBSP Concept Graphic|
This being a space business blog, I gravitated to interview those presenting ideas which were intriguing from a business perspective. You be the judge.
The first interview is with Al Globus. Al presented this paper at SM14 on a way to significantly reduce the size of a profitable (or nearly profitable) first-generation solar power satellite that could be launched on a single EELV for under $100M.
Q: Typical powersat plans require massive satellites in GEO. Talk about why this is and how your plan for space-based solar power is different.
Al Globus: The size of traditional PowerSats is driven by the choice of microwaves for power beaming. This requires km scale antennas on orbit. My plan uses infrared which reduces the size of the power beam by a factor of 30,000-120,000 (depending on assumptions). This means the on-orbit power beam can be just a few meters across, radically reducing the size of PowerSats.
Q: Your paper recommends powersats beam energy back to earth using infra-red instead of microwave wavelengths. What are tradeoffs between infer-red and microwave for powersat transmission and how you came to prefer infrared?
Al Globus: The big advantage is size. This is because the size of the beam is directly proportional to the wavelength and infrared is a much smaller wavelength than microwaves.
Disadvantages include: high energy density on the ground which is a safety concern, the state of the art is not good enough yet, and higher atmospheric absorption. In practice this may mean that powersats using infrared power beaming are limited to desert-like locations due to absorption by rain. Fortunately, there are large electricity markets in very dry regions such as Southern California, North Africa, and much of Australia. This is more than large enough to get SSP into the energy mix and pave the way for larger satellites that can serve more of the market.
Q: Talk about advances in thin film helio-gyros. What are they (for us non-engineers) and how can they help solution the space based solar power problem?
Al Globus: The advantage of thin-film heliogyros is mass (weight). First, the material is very thin and therefore very light. The power producing bits of the Ikaros satellite are only 32.5 microns thick and probably weigh about 45 g/m^2. A heliogyro does not use masts and rigging to hold the material facing to the sun. Instead, it spins. As a anyone who has played on a merry-go-round knows, spinning produces a force outward from the center. This is used to stiffen the solar-power absorbing materials. On Earth this could never work due to gravity, wind, etc. In space these are not an issue. The Ikaros only spins at 1-2 rpm which is sufficient to keep the material facing the sun.
Q: Talk about how you get a commercial power satellite up in only one EELV launch.
- First, you need to convert the Ikaros to a powersat by covering the entire sail area with thin-film solar cells.
- Second, you need to scale it up to 200+ m on a side (from 14m).
- Third, you need to develop the power beaming equipment with a 2.6 ton mass budget and mechanical constraints.
- Fourth, you need to keep the power beaming equipment cool.
- Fifth, you need 20% efficient solar cells.
- Sixth, you need to be able to get a bulk discount from SpaceX (promising to launch more PowerSats).
- Seventh, you need to do all this development for perhaps a hundred million of dollars or so.
- Eighth, you need to sell the power in remote places where the price is very high.
Q: Your paper describes the potential profitability of a 5MW power satellite by selling to niche markets. What niche markets are you considering?
Al Globus: US military forward bases. There is also evidence that certain Italian markets were willing to pay $0.29/kwh at at least one point in the past.
Q: You say in your paper, the easiest and most profitable powersat research area is system design. Why do you think that is and what are some beneficial research topics?
Al Globus: There is no really well thought out design for infrared power beaming from orbit to earth. While the paper is pretty specific on how to generate the power (based on the Ikaros, which is in orbit and works) the power beaming bits of the paper are more of an existence proof: finding bits and pieces of data here and there than indicate that there should be some design with the desired properties. However, knowing that there is a solution doesn't mean you know what the solution is. That's the purpose of this research: come up with actual point designs that could be tested.
Q: What should I have asked that I didn’t?
Al Globus: Are there others who have proposed similar ideas? Yes. Lots of people have looked into infrared power beaming for space solar power. However, as far as I know, this is the first time using heliogyros for power production has been proposed.
Why isn't the government funding R&D in this area? Good question. DOE spends about $400 million per year on fusion research and, while SSP is a difficult problem, it is a lot further along than fusion. After all, satellites in orbit regularly generate useful quantities of solar power, something fusion has never done. SSP's current budget: $0.