Peter Chen displays his 12-inch “moondust mirror.” AAS photo by Richard Dreiser © 2008 American Astronomical Society
Once upon a time, the buzzwords in telescope making were Teflon and Formica. In the future, though, they may be epoxy and lunar dust.
Peter Chen and his colleagues at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, presented a novel recipe for making telescope mirrors at the American Astronomical Society meeting in St. Louis June 4. For years, Chen has been exploring the use of composite materials in making lightweight, high-quality telescope mirrors with an eye to building big scopes on the Moon.
The key to building massive structures of any kind on the Moon is to use as many local resources as possible — “in situ resource utilization,” in NASA-speak. So, Chen’s team combined simulated moondust with carbon nanotubes. The result was a strong, thermally stable material with the consistency of concrete. Chen notes this stuff could be used as the building blocks of a lunar base.
The team poured layers of epoxy over a disk of this lunar concrete and spun the unit until the liquid cured. “I just used a pottery wheel,” Chen says, smiling. The result was a 12-inch-wide mirror blank with a parabolic surface. When they coated the blank with a small amount of aluminum, the researchers had a telescope mirror.
For building a lunar scope the size of Hubble, Chen’s process requires transporting 132 pounds (60 kilograms) of epoxy, 13 pounds (6 kg) of carbon nanotubes, and less than 1/3 ounce (1 gram) of aluminum. The remaining raw material required — 1,300 pounds (600 kg) of moondust — is already at the construction site.
But Chen is thinking much bigger than a lunar Hubble. "We could make huge telescopes on the Moon relatively easily," he says. "Since most of the materials are already there in the form of dust, you don't have to bring very much stuff with you, and that saves a ton of money."
He envisions monolithic mirrors as large as 50m across. That would take about 4,000 pounds (1,800 kg) of epoxy and a pound (about half a kilogram) of aluminum. How much lunar dust? “I don’t even want to think about that,” Chen says, laughing.
He suggests that future telescope makers might select a promising patch of lunar real estate and use robots to remove the rocks. Then solar concentrators — built using the same moondust-mirror material — could fuse the dust. Next, add layers of epoxy to create a smooth surface, then figure it to a parabola using ion beams, a process that would take advantage of the environment’s high vacuum.
Astronomers say a 50m lunar scope would let them record spectra from extrasolar planets and detect gases like ozone and methane, indicative of life. Add one or two more such scopes, and they could work together to directly image alien worlds.
That’s not a bad rationale for revisiting the Moon.