Space solar power appears to offer the cleanest option for generating the large quantities of electricity needed by a progressive civilization. Among other options for power generation, none has such benign environmental impact or is so safe. Space solar power would forestall nuclear proliferation and nuclear terrorism. It prevents the environmental damage of mining uranium and fossil fuels. Satellite solar power is particularly attractive for countries like China which depend on coal-fired power stations for most of their electrical capacity because coal smoke reduces China’s food production by an estimated 10%. The physics of the power transmission preclude its use as a weapon. What is needed is a demonstration of economic feasibility.
The market worldwide for base load electrical power generating stations is now $400 billion per year, and that number will increase for decades. If we develop a method to build satellite solar power stations that can deliver electricity at competitive rates, there could be a nearly $400 billion per year annual market for sales of the power stations alone.
The first designs for power satellites used radiofrequency power transmission. Thirty years ago NASA demonstrated radio frequency power transmission efficiency comparable to power transmission over long terrestrial power lines. The power satellite transmitting antenna must be one kilometer in diameter to achieve that efficiency. The development cost and capital cost of such large systems made a powersat construction program too risky to undertake. Advances in laser power transmission make it possible to build smaller power stations with much lower capital and development costs. The cost of electricity should be competitive with ground-based solar in places with an adverse climates. Such a laser transmission system is described by SSI researcher Prof. Martin Hoffert.
Generating electricity in space and transmitting it to end-users on the Earth offers significant benefits over ground-based solar power. The sun shines continuously in geostationary orbit, except for two brief periods during the equinoxes. Solar power in space is not reflected by clouds, nor is it attenuated by the atmosphere. A power station in high orbit receives more than four times as much energy as the best ground-based sites and about six times more than the average site. To provide continuous power, a ground-based solar power installation requires electrical storage backup roughly equal in cost to the cost of the generating equipment. So the capital cost of ground-based solar power should be much more expensive than the capital cost, excluding transportation, of mature satellite solar power. The receiving stations can be located close to the electricity demand and so avoid the 10-20% transmission losses through long transmission lines. For radio frequency transmission, the receiving antennas are transparent to sunlight, allowing farming of the land beneath the receiving antenna. Power transmission can be switched from one place to another to follow demand.
The cost of satellite solar power stations is determined primarily by the cost of transportation to low Earth orbit. Because of remarkable progress in the technology for low cost space transportation, we believe that costs will fall to a few percent of its present value within the next 15 years. That lower cost should make satellite solar power economically competitive for some applications, the National Security Space Office identified a need for satellite power stations with a capacity of 5 MW. A successful satellite solar power demonstration on this scale will provide demand to develop even lower-cost space transportation.
SSI believes, however, that the most cost effective satellite solar power stations will be built from materials mined from the Moon or asteroids. To make that argument, robust industrial processes to get engineering materials from the Moon are needed, and except for SSI’s work, little work on non terrestrial materials has been done. The Moon offers materials to build low technology and low-cost, but heavy, satellite solar power stations. The technology for electromagnetic launch from the Moon has improved enormously in the past three decades. An efficient mass driver using the SSI design could be constructed with the ultra-capacitors and high-power solid-state switches currently sold to the automotive market. A mass driver placed on the Moon could launch annually many thousands of tons of construction material for satellite power stations into high Earth orbit. The marginal cost for launching material from the moon to high Earth orbit is calculated to be a few percent of the cost of launching the same material from the Earth because the lunar escape energy is five per cent of that from the Earth and mass drivers are both cheaper and more efficient than rockets. See “The World’s Energy Future Belongs in Orbit” on ssi.org.
There are many possible technical options for power conversion in a power satellite. We do not know which of these options will be the most economical. It would be a grave mistake to prematurely specify the power generation subsystem. The government made that mistake with nuclear power, commercializing a system that had been optimized for military use. It would be a mistake to assume that either heat engines or thermionic conversion cannot compete with photovoltaic cells, particularly if most of the material to construct the power satellite is sourced from the Moon.
Satellite solar power is inherently geopolitically stabilizing. When economical power satellites are built, all countries will want them. All countries will therefore desire peace on the High Frontier. Power satellites are not vulnerable to terrorists, but they would be vulnerable to attacks by any of the major space faring powers.
The National Security Space Office has identified a tactical and strategic need for space solar power. It is unfortunate that one of the most promising eternal power sources is otherwise an orphan in the Federal Government.
Lee S. Valentine
