Sandia LabNews

A space-based polymer mirror that can be reshaped on the fly

In March 2008, Sandia researchers sent space-grade polymers to the International Space Station to see whether the inexpensive lightweight material, with its easily changeable shape, could replace expensive orbiting telescopic mirrors made of polished glass or beryllium.

“A conventional telescope mirror takes 18 months to two and a half years to manufacture,” program manager Jeff Martin (2617) says. “You have to order it exactly and you can’t change it. It’s the long tent pole in a satellite system.

“But a polymer mirror with a controllable shape opens up space missions that couldn’t otherwise exist. Apply a voltage to its piezoelectric-coated surface and it changes curvature to create the surface you want.”

The work envisioned controlled changes in curvature similar to the more expensive technique called adaptive optics, which changes the alignment of submirrors to alter the overall shape of a telescope’s mirror by hundreds of nanometers.

 “But a polymer mirror’s shape can be altered by hundreds of micrometers,” points out Sandia principal investigator Mat Celina (1821), “and in a continuous fashion.” A polymeric mirror would also be far less expensive.

To monitor degradation of materials sensitive to the strong UV and atomic oxygen found in the harsh environment of low Earth orbit, Mat’s team secured Sandia’s place in the MISSE-6 program, the first time the Labs was so involved.

NASA’s Materials on the International Space Station Experiment (MISSE) program, under the direction of the Naval Research Laboratory, provides opportunities to researchers for low-risk, quick, and inexpensive flight tests of materials and equipment in space aboard the International Space Station (ISS).

Sandia researchers equipped their experiment with solid-state data loggers to record declining function over time.

These experiments, designed by Mat, Tim Dargaville, and Gary Jones (all 1821) were the first of their kind to activate piezoelectric materials and record their responsiveness during cumulative space exposure. They were also the first active MISSE experiment. “We also exposed passive samples for comparison,” says Mat.

The process applied voltage to a bimetallic strip to make its tip go up and down. The extent of motion was recorded.

“Over time, that amplitude should get smaller and smaller,” says Jeff. “Of course, if these materials were phenomenal, there would be no degradation.”

How phenomenal is still an open question. The experiment, expected to be in space for six months, was there for a year and a half because the Columbia shuttle disaster delayed subsequent launches. The materials returned to Earth in September 2009, and were returned to Sandia researchers for analysis in November. Piecing together the results could take as long as a year.

The plastic material is a polyvinylidene fluoride (PVDF) copolymer, a material that can be produced in large plastic sheets. Big rolls are available at Lowe’s, Jeff says. “An extra processing step makes it shrink or grow when you apply a voltage. We invented a new flavor to get the best advantages in a space environment.”

The work is funded by Sandia’s Laboratory Directed Research and Development office.