Space Studies Institute/Space Research Associates Study In 1983 the Space Studies Institute decided to examine designs for a Solar Power Satellite intended from the start for construction from lunar sources of supply. A Request for Proposals was written and in 1984 a contract awarded to Space Research Associates (SRA) of Seattle, Washington. The primary design requirement specified was minimal non-lunar mass. Future work in this area by the SSI includes the development of glass fibre-glass matrix composites which could be produced from lunar soil components, and advances in Stirling cycle engines for space power applications. The General Dynamics SPS design required only 10% as much Earth mass as the Earth baseline design [1], However, the rules of the study allowed only minor changes to the Earth baseline design and did not consider using lunar material for any system which comprised less than 1.2% of SPS mass. Thus, the design did not establish a lower boundary on non-lunar mass. The SSI/SRA design study emphasized minimal use of Earth-supplied mass to achieve low cost; any design consistent with this emphasis was acceptable. The ground rules of the study are listed in Table 1. Elements abundant on the Moon are aluminium, calcium, iron, magnesium, oxygen, silicon, and titanium. Less abundant but potentially available are chromium, potassium, manganese, and sodium; there may be some technological or economic risk in planning to use these materials. Nickel is a component of some micrometeorites which are present in tiny amounts in lunar regolith. These micrometeorites are high- quality steel and should be easy to separate magnetically from the regolith [2]. Thus, using nickel steel was assumed to be a reasonably good risk. It was found that an SPS can be designed which uses less than 1% as much non- lunar material as the Earth baseline SPS, a factor-of-ten improvement over the results of the General Dynamics study. Most of this improvement was achieved by using Table I. Study ground rules • Any reasonably abundant chemical element present in lunar material could be mined, refined, and transported to the SPS construction site. All other materials must be transported from Earth. • The primary design requirement was minimal non-lunar mass. Low total mass was only a minor concern. • Scope of the study did not include design of transportation systems, materials processing, or assembly systems. • To enhance commercial feasibility, undemonstrated technology was avoided in the design wherever possible. • Only microwave transmission of power was considered. The peak intensity at the ground could not exceed 300 W/m' 2.
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