A Moon-Based Telescope
NASA scientists have developed a simple and inexpensive method for turning lunar dust into a concrete-like material that can be used instead of glass to build large telescope mirrors on the moon. The scientists made the material by mixing carbon nanotubes and epoxies–glue-like materials–with a crushed rock compound that has the same composition as lunar dust. Then they spun the material on a pottery wheel to create a mirror blank with the parabolic shape of a telescope mirror.
Building a telescope mirror in which 90 percent of it is made from moon dust means that the few remaining parts can be carried to the moon, and scientists are no longer limited with regard to the size of the telescope they can make, says Peter Chen, a scientist at Goddard Space Flight Center who’s working on the new method.
The power of a telescope is proportional to the size of its mirror. The James Webb Space Telescope, which is scheduled to succeed the Hubble telescope in 2013, will be the largest to fly to space with a mirror that is six meters in diameter. Chen says that, using the new method, scientists could build mirrors on the moon that are 50 meters in diameter–the ideal size to peer deep into the universe, find Earth-like planets in our solar system, and search for the presence of life.
Indeed, say experts, the moon is an ideal spot for astronomy. “The moon has no atmosphere, which means no blurring or absorption of starlight, and it provides a large, stable platform,” says Chen.
Chen’s group is not the only one working on an approach to build giant, powerful mirrors on the moon. Scientists Robert Angel, at the University of Arizona, and Ermanno F. Borra, at the Université Laval, in Quebec, are working on a spinning liquid-mirror telescope. While both methods have similar goals, they have different technical challenges, says Angel. The liquid-mirror telescope has to be spun at an accurate rate throughout its lifetime, and thus can only point in one direction. “If the NASA scientists can freeze their liquid surface into something accurate–epoxy mirrors change shape when they set–they can make a more versatile telescope than ours,” says Angel.
Most telescope mirrors are made of highly specialized materials, like beryllium or silicon graphite, that are rare and expensive. Using these to make large, perfectly smooth optical surfaces is also an involved process. Very tiny flaws in the materials can make a mirror unusable.
In contrast, NASA scientists used a combination of readily accessible materials: carbon nanotubes, epoxies, and a crushed rock that has the same composition and grain size as lunar dust. The mixture created a very strong material with the consistency of concrete. The scientists then added another layer of epoxy and spun the material to generate a 12-inch-wide mirror with the parabolic shape of a telescope mirror. Although spinning epoxy is unlikely to freeze the mirror into a perfect optical surface, it is easy to adapt standard industrial processes to make telescope mirrors of high quality and smoothness, says Chen. He and his group have also developed a noncontact method called reactive ion etching, which they have shown can modify the epoxy surface at will, remotely.
“Demonstrating this [method] on a 12-inch mirror is just a first small step towards what it would take to build a production facility capable of making a 50-meter telescope,” says Lee Feinberg, a NASA scientist who manages the James Webb telescope.
A major concern regarding equipment constructed on the moon would be keeping high-precision mechanical surfaces (joints, bearings, and so on) from being clogged by dust. There are also large temperature swings between daytime and nighttime that would place high demands on the integrity of the moving mechanical parts.
But first, NASA has to get to the moon, a feat that it hopes to accomplish by 2020.
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