June 21, 2000
Power is always a problem in space, because energy sources such as solar panels and nuclear reactors are heavy and expensive to launch, and spacecraft have limited capacity. But, as luck would have it, the Moon has everything that's needed to make solar panels, according to Alex Freundlich, a physicist at the University of Houston who is working on a fledgling project funded by the NASA Institute for Advanced Concepts.
The Moon has silicon, metals and other necessities in its rocks -- and no atmosphere. The place is one big vacuum, much better than those that can be created on Earth in microchip manufacturing machines. The vacuum is critical, because it eliminates outside forces that could push molecules off-track or cause contamination.
Freundlich and his team are exploring the concept of a Moon rover capable of building whole fields of solar cells. As the first stage in this tentative scheme, a solar-powered rover would be sent with enough raw materials to build solar cells that could generate around 100 kilowatts of electricity.
The manufacturing process would draw energy from a series of lenses that concentrate the Sun's heat. A lens at the front of the rover would melt regolith -- Moon dust -- to make a glass base for the cells. The vehicle would then move forward and deposit a layer of aluminium as an electrode on the new base. The metal would be heated until its molecules began to evaporate, spraying through nozzles under gravity.
After laying down the aluminium, the rover would move forward again and deposit the first layer of silicon, followed by a layer of dopants -- the trace elements used in making semiconductors. When all the necessary layers were applied, they would form solar cells in which the active region was just a few micrometres thick.
Freundlich says the cells would be less efficient than those made on Earth because the materials would be of lower quality. However, they would be free and unlimited once the system was in place, so the benefits would far outweigh any disadvantages.
The next stage would move towards full use of Moon resources. A second spacecraft would deliver a "robotic refinery", to be powered by the solar cells, for extracting other substances from Moon rocks.
Freundlich hopes to have a prototype rover built within the next few years and thinks that the first stage of the concept could be realised within the decade. The team will also be looking at whether they can modify the technology for use on Mars.
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