April 27, 2001

Lab gives Keck a protective coat

Two Lab scientists, Jesse Wolfe of Electronics Engineering Technology Division, and Norman Thomas of Chemistry & Material Sciences, together with their team of supporters, have patented a new ultra-thin silver coating for mirrors, which is proving to be far more durable than any previously used.

"Mirrors used in telescopes and lasers around the world, and in space, suffer significant efficiency losses due to the deterioration of the mirror coatings," said Thomas, principal investigator on the project. "On earth, numerous air-borne factors, from smog to automobile pollutants to ocean salt, can rapidly affect the coatings.

"In space, the mirrors often deteriorate due to the impact of atomic oxygen and micrometeorites, and exposure to solar radiation, temperature extremes and other contaminants. Our new coating is showing signs of being virtually indestructible in terrestrial conditions, and we’re very excited that it will be exposure-tested on the International Space Station as of this spring."

The coating was recently installed on a 22-inch mirror for use at the Keck Observatory in Hawaii, where, Thomas reports, "the astronomers are just ecstatic." The mirror coating is scheduled for use in several of the world’s major telescopes within the next few months, including Kitt Peak in Tucson, Ariz., and possibly the South African Large Telescope (SALT) and, in the more distant future, the California Extremely Large Telescope (CELT).

Thomas explained, "These large telescopes typically involve five or six reflections from coated mirrors, which affect the collection efficiency. Our coating is going to give each mirror a consistent 97 percent reflectivity. Previous coatings provided about 90 percent reflectivity. Combine the effect from several mirrors, and we may have up to 35 percent increased collection efficiency for many years from each of these large telescopes."

This coating is also being installed to protect the thousands of mirrors to be used in the NIF flash lamps, according to Wolfe. "Many intense hours, many of them volunteer, have paid off in a revolutionary protection for NIF, the world’s top astronomical observation equipment and components of the international space station."

"In fact," added Thomas, "this project began in support of NIF, then funding was secured from NASA, the Air Force and Lockheed-Martin due to the great potential for use in both the Hubble telescope and the Spaced-Based Laser program."

When Wolfe and Thomas’ samples of their new silver coating go with the shuttle to the International Space Station this June, they will travel in a small suitcase with samples of other materials being tested for space applications. An astronaut will have to take the suitcase out by hand in an extra-vehicular activity (EVA) mission, and secure it in the initial test area.

In this experiment known as MISSE (Materials on International Space Station Experiment), the various samples will be tested in one- and three-year periods, exposed in both the ram and leeward directions, in full sunlight and in the earth’s shadow.

Other control samples will be tested during the given times for degradation during storage on earth. They must show sufficiently low rates of degradation over a useful period to qualify for service on the space station and other space-based applications.

Wolfe and Thomas have been pursuing this project for over three years, but have had their work involved with space missions before, as scientists for Optical Coating Laboratory, Inc. in Santa Rosa. In 1984, shuttle astronauts placed some of their samples in the Long Duration Exposure Facility, an orbiting framework used for the testing of various materials in space. The samples were retrieved in 1990, and results helped lead to this latest invention.