Solar Power from the Moon
Section 2.8.
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Uses for Photovoltaic Cells Produced on the Moon

Most current plans for a lunar base assume that the base will include an industrial facility, primarily to produce oxygen for propulsion systems by reduction of the lunar soil [1]. A second product for such a facility could be solar arrays. While the primary user of lunar- produced solar cells would undoubtably be the lunar base itself, there would be many markets. Figure 1 shows some of these possible uses of lunar produced photovoltaics, including solar- electric propulsion for orbital transfer vehicles and for solar system exploration, and power systems for geosynchronous Earth orbit (GEO) and low Earth orbit (LEO) satellites.

Use of lunar-manufactured solar cells for high-power solar-electric propulsion is an especially attractive option. Recent proposals for a manned Mars mission [2], for example, propose an unmanned, electric-propulsion cargo vehicle to ferry supplies to Mars orbit in advance of the crew on a low-thrust orbit. The power system for the electric propulsion is a 5 MW nuclear generator, which could be replaced with lunar-manufactured thin-film solar cells for a considerable savings in required weight to orbit. For a "sprint" mission, a high-power electric propulsion vehicles of 200 MW power and a specific impulse of 20,000 sec could make the round-trip to Mars as short as 7.5 months [2].

Solar-electric transport vehicles would also greatly reduce the required mass for servicing the lunar base itself. B.G. Logan [3], for example, proposes a 6 MW Manned Lunar Shuttle powered by a pulsed plasma gun, estimating that this could halve the transport costs, even for relatively modest specific power solar arrays.

Use of lunar material has also been widely proposed for manufacture of solar cells for satellite solar power stations [4].

The cost of transportation from the Earth's surface to orbit and beyond can be quite high. Figure 2, for example, shows the cost of delivering conventional and advanced power systems to orbit, the moon, and Mars, using cost estimates typical of current technology space boosters. For example, a one-megawatt power system delivered to Mars could have transportation costs alone in the ten to hundred billion dollar range. While these costs are likely to be decreased with advanced transportation, they are likely to remain high.

The advantage of lunar manufacture is that the escape velocity is only 22% that of the Earth. Table 1-A shows the Delta-V (velocity increment) needed to achieve various destinations from the Earth's surface and from the moon.

The payload fraction decreases exponentially with the delta-V, and a much higher fraction of the lift-off mass can be useful payload, as shown in table 1-B, which shows the theoretical maximum fraction of lift-off mass which can achieve the listed orbit if launched from the Earth's surface, compared to launched from the moon. (Actual rockets never achieve these values; typically only 1-2% of the mass of a rocket launched from the Earth is useful payload.) Even to low Earth orbit, five times the payload can be delivered if launched from the moon than if launched from the Earth's surface. For the commercially valuable geosynchronous orbit, almost nine times the payload can be delivered. This is a strong leverage factor for lunar manufacture.

The design criteria for lunar manufactured solar cells depends on the mission. The most important criteria for most missions are maximum power/weight ratio (specific power) and minimum usage of materials transported from Earth. For use on the lunar surface, specific power is not an important criterion.

-- Geoffrey A. Landis


(1) Lunar Bases and Space Activities in the 21st Century Symposium, 5-7 April 1988, Houston, TX.

(2) NASA Office of Exploration, Exploration Studies Technical Report FY 1988, Vol. 1, NASA Technical Memorandum 4075, 21-22 (Dec. 1988).

(3) B.G. Logan, "Initiative for the 21st Century: Advanced Space Power and Propulsion Based on Lasers," presented at NASA Lewis April 25-26, 1988; Lawrence Livermore Laboratory preprint UCRL-98520.

(4) G.E. Maryniak and B. Tillotson, "Design of a Solar Power Satellite for Construction from Lunar Materials," Space Power 7, No. 1, 27-36 (1988).

Solar Power from the Moon

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