NASA scientists produce first-ever carbon nanotube mirrors

A lightweight telescope that a team of NASA scientists and engineers is developing specifically for a small satellite known as CubeSat could become the first to carry a mirror made from carbon nanotubes.

Led by Theodor Kostiuk, a scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, the team is developing a compact, reproducible and relatively inexpensive telescope that would fit easily inside a CubeSat, which has sides that are just four inches long.

Small satellites such as CubeSats are playing an increasingly important role in exploration, technology demonstration, scientific research and educational investigations at NASA, providing a low-cost platform for many missions and projects. These include planetary space exploration, Earth observations, fundamental Earth and space science, and the development of precursor science instruments like cutting-edge laser communications, satellite-to-satellite communications and autonomous movement capabilities. Small satellites also offer an inexpensive way to engage students in all phases of satellite development, operation and exploitation.

Kostiuk's team is seeking to develop a CubeSat telescope that will be sensitive to ultraviolet, visible and infrared wavelengths of light. Equipped with commercial-off-the-shelf spectrometers and imagers, it will be ideal as an "exploratory tool for quick looks that could lead to larger missions," Kostiuk explained. "We're trying to exploit commercially-available components."

With funding from Goddard's Internal Research and Development program, the team is currently testing the telescope's overall design by producing a laboratory optical bench containing three commercially-available, miniaturized spectrometers optimized for ultraviolet, visible and near-infrared wavelengths. Fiber optic cables will connect these spectrometers to the focused beam produced by a three-inch diameter carbon nanotube mirror.

Unlike most telescope mirrors, which are made of glass or aluminum, this particular optic is made of carbon nanotubes embedded in an epoxy resin. Sub-micron in size and cylindrically shaped, carbon nanotubes exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat. Because of these unusual properties, carbon nanotubes are finding use in nanotechnology, electronics, optics and other fields of materials science, and, as a consequence, are being used as additives in various structural materials.

"No one has been able to make a mirror using a carbon nanotube resin," said Peter Chen, a Goddard contractor and president of Lightweight Telescopes, a Columbia, Maryland-based company working with the team to create the CubeSat telescope.

"This is a unique technology currently available only at Goddard," he continued. "The technology is too new to fly in space, and first must go through the various levels of technological advancement. But this is what my Goddard colleagues are trying to accomplish through the CubeSat program."

The use of a carbon nanotube optic in a CubeSat telescope offers a number of advantages, said Goddard scientist Tilak Hewagama, who contacted Chen upon learning of a NASA Small Business Innovative Research program that was awarded to Chen's company to further advance the mirror technology. In addition to being lightweight, highly stable and easily reproducible, carbon nanotube mirrors do not require polishing – a time-consuming and often expensive process that is required to assure a smooth, perfectly shaped mirror, said John Kolasinski, a Goddard engineer and science collaborator on the project.

To make the mirror, technicians simply pour the mixture of epoxy and carbon nanotubes into a mandrel or mold fashioned to meet a particular optical prescription. They then heat the mold to cure and harden the epoxy. Once set, the mirror is coated with a reflective material made from aluminum and silicon dioxide.

"After making a specific mandrel or mold, many tens of identical low-mass, highly uniform replicas can be produced at low cost," Chen said. "Complete telescope assemblies can be made this way, which is the team's main interest. For the CubeSat program, this capability will enable many spacecraft to be equipped with identical optics and different detectors for a variety of experiments. They also can be flown in swarms and constellations."

A CubeSat telescope is just one possible application for the optics technology, Chen added. He believes that carbon nanotube mirrors could also work in larger telescopes, particularly those comprised of multiple mirror segments. For example, 18 hexagonal-shape mirrors form the James Webb Space Telescope's 21-foot primary mirror, while each of the twin telescopes at the Keck Observatory in Mauna Kea in Hawaii contain 36 segments that form a 32-foot mirror.

Many of the mirror segments in these telescopes are identical and could therefore be produced using a single mandrel. This approach would avoid the need to grind and polish many individual segments to the same shape and focal length, thus potentially leading to significant savings in time and cost.

Moreover, carbon nanotube mirrors can be made into 'smart optics'. To maintain a single perfect focus in the Keck telescopes, for example, each mirror segment has several externally mounted actuators that deform the mirrors into the specific shapes required at different telescope orientations.

In the case of carbon nanotube mirrors, however, the actuators can be incorporated into the optics at the time of fabrication. This is accomplished by applying electric fields to the resin mixture before curing, which causes the carbon nanotubes to form chains and networks. After curing, the shape of the optical surface can be altered by simply applying power to the mirror. This concept has already been proven in the laboratory.

"This technology can potentially enable very large-area technically active optics in space," Chen said. "Applications address everything from astronomy and Earth observing to deep-space communications."

This story is adapted from material from NASA's Goddard Space Flight Center, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.