Bush's plan, announced a year ago, envisages a permanent lunar base from which people can go out and explore the moon, and then go on to Mars. "We will need a power source," says David Williams, a planetary and lunar scientist at NASA's National Space Science Data Center in Greenbelt, Maryland. "Bringing stuff up from Earth is really expensive."
Four years ago, Alex Freundlich and his colleagues at the University of Houston in Texas came up with the idea of getting robotic rovers to build solar cells entirely out of lunar dust or "regolith"(New Scientist, 24 June 2000, p 14) . This fine, grey powder is half silicon dioxide, with the remainder made up of a blend of oxides of 12 metals, including aluminium, magnesium and iron. The team reasoned that this mix contains all the elements necessary to build a solar panel, and suggested that robots trundling over the lunar surface could melt regolith, refine it and then lay down a glassy substrate on which solar cells could be deposited. The rover- solar-powered of course- would leave a trail of solar panels in its wake.
Now Freundlich and his team have shown that a key part of this plan should work. They simulated what the rovers will do inside a vacuum chamber, which they used to get as close as possible to the moon's near-perfect vacuum. They melted a powder called JSC-1, which has a composition identical to the samples of regolith brought back by the Apollo astronauts, and then let it resolidify as a smooth, glassy sheet.
The researchers then showed that a solar cell deposited on the surface of this sheet by thermal evaporation converts light into electricity. They report their work in the latest edition of Acta Astronomica (vol 56, p 537).
Demonstrating that the base of a solar panel, which makes up the majority of its mass, could be built entirely out of lunar dust is a big step, Freundlich says. The team's experiment showed, for example, that the glassy re-formed regolith is smooth enough to serve as a substrate for the micrometre-thick layers of the solar cell, and tough enough not to crack. Such flaws in the base of a solar cell would wreck it by bringing oppositely charged electrodes into contact with each other, causing short circuits. For future tests, they plan to work out how to make the semiconductor parts of the solar cell using silicon extracted from the regolith.
The researchers were careful to employ only techniques that would be available to them on the moon. This meant that the solar cells they produced were inefficient. While conventionally produced solar cells convert up to 20 per cent of the energy falling on them, the simulated lunar panels were only 1 per cent efficient. However, this may not matter on the moon, where real estate is virtually unlimited.
Author: Celeste Biever
This article appears in New Scientist issue: 22 JANUARY 2005
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