University of Nebraska-Lincoln


Lincoln (Neb.) -- Feb. 6, 1998 -- Dr. John Woollam is a solid-state physicist and an electrical engineer, not a physician.

But fellow scientists and engineers at the National Aeronautics and Space Administration and the Russian Space Agency may be forgiven if they think of the University of Nebraska-Lincoln professor as something of a gerontologist and opthamologist for satellites.

That's because in recent weeks Woollam and his Nebraska team, in collaboration with NASA space scientists, have come up with a "cure" for a contamination problem that was accelerating the aging process of the Russian space station Mir and have begun diagnosing a problem that potentially threatens the vision of the Hubble Space Telescope.

Woollam's lab in the Center for Microelectronic and Optical Materials Research in the College of Engineering and Technology recently received from NASA postage stamp-size samples of surface materials from each satellite to analyze their contamination problems.

Woollam wears many hats as the director of the center, George Holmes distinguished professor of electrical engineering and professor of physics and astronomy. He explained that when objects are in orbit, they are exposed to a harsh environment that includes heavy ultraviolet radiation and radiation from solar flares. In addition, he said, objects in low orbit -- 100 miles up or so -- are exposed to tiny amounts of oxygen in the Earth's upper atmosphere. Oxygen, which normally exists as molecules consisting of two oxygen atoms, often becomes dissociated when exposed to the sun at high altitude. That is, the oxygen molecules split into their individual atoms and oxygen in its atomic form reacts strongly with many materials.

Woollam said Mir had a severe contamination problem on portions of its exterior surface and it was necessary to identify the contaminant before it could be eliminated.

"There were regions of this material in which there were deposits of the contamination and regions in which there was not," he said. "Our experiments determined absolutely without a doubt that the contaminant was silicon dioxide that had been deposited during the space flight."

With that knowledge, NASA was able to examine the physical layout of Mir and analyze the history of its orbits to find the source and cause of the contamination. It turned out, Woollam said, that there was a region of the space station that the Russians had painted with silicone paint that overheated during orbits when the craft didn't pass through the Earth's shadow. The paint vaporized and adhered to other parts of the craft, causing the contamination. As a result of the Nebraska research, it will now be possible for Mir's crew to shield the silicon-painted area during extended exposure to the sun, preventing further contamination.

The Hubble's problem that Woollam's team has recently begun to analyze also involves the fragility of its covering materials.

"There's a polymer blanket on part of the spacecraft that went up as a flexible material, but it's becoming brittle because of exposure to the space environment," Woollam said. "That brittleness means it can break off and settle on the optics of the telescope and really mess things up.

"It's very important to figure out the origins of that brittleness and how to cure it, then later space shuttle flights can go up and replace that blanket."

Much of Woollam's research has been conducted with ellipsometers, devices that use reflected polarized light to detect properties of materials and make precise measurements of films that are only an atom or two thick. His lab recently developed an ellipsometer that enables researchers to work with infrared light, adding a whole new analysis capability.

"We can examine the chemistry of ultrathin films in ways people hadn't been able to do before," Woollam said. "We can analyze films that are 100 nanometers (100 billionths of a meter) thick that we couldn't before. Another virtue of this technique is it's totally nondestructive. The light beam we're using has an extremely weak intensity so we don't further damage the film."

Woollam came to Nebraska in 1979 as he was wrapping up a 13-year career as a research physicist at the NASA Lewis Research Center in Cleveland. He has maintained his ties with NASA, allowing him to continue doing the kind of hands-on space-related research he loves while getting NU students involved in the space program. On three different occasions, Nebraska students have sent experiments into orbit on shuttle flights.

"I get a big kick out of working and dealing with actual space shuttle flights -- and the students get really excited about it," he said. "Working with the space program is just downright good fun and any of my students would say the same thing, but probably with even more gusto."

The students who helped analyze the Mir and Hubble materials were Corey Bungay, a graduate student from Lincoln, and Brad Dworak, a senior electrical engineering major from Omaha.

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