Congress Gets an Update on Solar Power Satellites

Solar Power Satellite The House Science Committee's Subcommittee on Space and Aeronautics held hearings today on the Solar Power Satellite (SPS) concept today. Solar Power Satellites were first proposed in 1968 by Dr. Peter Glaser from the Arthur D. Little Company. The core of the concept is the use of large photovoltaic arrays placed in geostationary orbit around Earth. These satellites would be huge - possible a kilometer or more in length. They would capture solar energy, convert it into electricity, and send it to Earth via a powerful microwave beam. This energy would be captured on earth by a large antenna ("rectenna"), converted back into electricity, and fed into existing terrestrial power grids.

Space and Aeronautics Committee chair Rep. Rohrabacher said that further technology development is necessary before an economically viable SPS program can be contemplated. He felt that this can happen and said that a greater push for these efforts is needed.

Rohrabacher added that "the economics of SPS will likely rely upon the development of cheap access to space" another reason he supports SPS research He added that it may be possible to use existing launch systems to do basic technology demonstrations in space.

In citing the need for new energy sources, Rohrabacher said that oil prices are at one of the highest points ever and that they are reaching new heights. Rohrabacher said "this should be a signal to us to be looking for new sources of energy. In California we are suffering from major electrical shortages at this time. We should not be telling people to drop their standard of living. Instead we should be looking for new, cleaner sources of energy." Noting his previous stance on environmental issues he said "I may not believe in global warming but I do want cleaner air." At the time that the SPS concept was first studied, according to NASA's John Mankins, Department of Energy (DOE) studies showed costs of up to $275 billion before the first power would actually be generated. With the economics of this venture not readily apparent, and technology issues unresolved, NASA and DOE work was eventually terminated in 1980. At the time that this work ended, the NRC suggested that the topic be revisited in 10 years or so.

In the following years, technology research was conducted by a variety of research groups. According to Mankins, this interim research eventually showed that the SPS concept could be much more viable. This prompted NASA to conduct a "Fresh Look" study into SPS concept in 1997. It was this study that served as the core of the last hearing held on this topic. Today's hearings sought to measure the progress made since 1997.

One of the main technology drivers in SPS studies has been the cost and weight of a spacecraft in relation to the actual amount of power generated. Mankins cited a number of technological developments In the past year or so. One particular project involved solar array research based upon improving the current DS-1 probe's array. This project produced working concepts that would lead to a generating capability of 170 watts/kg of solar array. This represents a 3.5 fold improvement upon the current efficiency of the DS-1 photovoltaic array. According to Mankins "this leads us to think that high efficiency/low mass power generation is indeed possible."

Another concern in earlier SPS studies has been the efficiency with which power is transmitted from one point to another. Recent laser and microwave research has shown additional improvements in efficiency - this also lends support to the economic and engineering viability of the SPS concept. Mankins added that in addition to the power generating capabilities of SPS systems, large amounts of space-based, beamed power might also be required if large solar sail propulsion technologies are to be used for interstellar probes at the end of this century.

The SPS concept was originally envisioned as being a relay system for power generated in space with microwaves used as the means of relaying power. This concept has expanded over the years to include the use of lasers instead of microwaves. One reason being that microwave beams tend to diverge as they traverse large distances whereas coherent sources such as lasers exhibit much less divergence. The more divergence in an energy beam, the larger the antennas need to be at the reception/reflection locations and the greater the potential for lost power during transmission. Use of lasers would tend to minimize this concern. The SPS concept has also expanded to use space based satellites to relay power generated on Earth from one location to another - perhaps from an equatorial desert region to a large city further from the equator.

Ralph Nansen, President, Solar Space Industries, Inc. said that Use of SPS as a relay point of power from one region on earth to another may served an interim step in demonstrating the technical and economic viability of beamed power systems. He suggested that primary development of an SPS system should be commercial. But since this would be such large an effort, it should start as government/industry partnership. The government's role would be to set regulatory environment, provide loans and other funding for basic research, and be willing to accept the risk of buying the first SPS satellite. A lead agency should be designated according to Nansen. He felt that DOE is a natural choice with NASA providing support.

Nansen said that a ground test program should be funded to demonstrate separate technologies and develop a small prototype of the system on the ground. Efforts should also be made obtain frequency allocation for microwave transmission systems and that support be given to developing a more efficient launch infrastructure including loan guarantees for RLV (Reusable Launch Vehicle) systems.

Jerry Grey, from the American Institute of Aeronautics and Astronautics (AIAA) spoke about a study nearing completion by the AIAA. The AIAA has had a continuing interest in the SPS concept since its first description in 1968. The AIAA study looked at SPS work being done outside the US; the prospects for multiple uses of SPS technology; and a technical assessment of SPS work done by NASA. According to Grey, the study does not address economic or environmental considerations since these are being handled by other research groups.

While the draft AIAA assessment is still under review, Grey was able to say that the AIAA feels that SPS is a viable concept, and that it is one key area requiring an enhanced focus upon advanced launch system. He also said that the AIAA group has expressed a particular interest in using SPS concepts to augment the existing terrestrial power grid. This would involves relaying energy. Reflection of sunlight; reflection of sunlight and conversion to/from microwaves; and the use of lasers were all examined. It was felt that geostationary satellites are preferred over satellites in lower orbits for control reasons. Sunlight and microwave reflection via geostationary orbit is not feasible because of beam diversion. Lasers, however, have far less beam diversion and are very efficient.

Rohrabacher closed the hearing by saying "we spent billions of dollars on fusion research - perhaps as much as $20 billion - and we don't have anything to show for that. People often call this 'white coat welfare'. You have to ask why we should be doing this. I don't think we should be spending money just to advance knowledge. Projects such as SPS can lead to the bettering of people's condition on this planet. I think that some of the money that was spent on fusion could have been spent on SPS and that it could have yielded clean energy from space by now had we done so. "

He went on to say "we need to set priorities. I think this is a fundamentally good idea. I don't know if we are there yet, but from what I heard today it seems to me that we should move forward with this. We should not just pump money into this for the sake of pumping money. I think that my zero gravity/zero tax concept could serve as an incentive to this support this research and spur investment. We still have more work to do before we tell the private sector that we're ready to rock and roll and start launching the rockets.

Ralph Nansen added that we have enough technology today to start serious work on SPS systems. "We don't need any breakthroughs. We need to apply what we already have here on the ground." Rohrabacher ended the hearings by saying " it seems that we just need to take what we already have and put it together and let it do what it needs to do."

Related Links

° Testimony of Ralph Nansen, 7 September 2000
° Testimony of Molly Macauley, 7 September 2000
° Testimony of Jerry Grey, AIAA, 7 September 2000
° Testimony of John Mankins, NASA HQ, 7 September 2000

Background Information

Statement of John C. Mankins Manager, Advanced Concepts Studies Office of Space Flight, NASA, before the Subcommittee on Space and Aeronautics Committee on Science House of Representatives, October 24, 1997
An Evolutionary Path to SPS by Geoffrey A. Landis, NASA Glenn Research Center
Developing the Case for Solar Power Satellites, by Alan M. Ladwig, Associate Administrator for Policy and Plans, NASA Headquarters. Paper Presented at SPS '97 Energy and Space for Humanity, Canadian Aeronautics and Space Institute, Montreal, Canada, August 25, 1997
SUNSAT Energy Council
Solar Power Satellites - August 1981 report on solar power satellites by the Office of Technology Assessment
Solar Power Satliite Resources, SpaceRef Directory

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