Ultra-light space telescopes challenge ingenuity

SIGNS OF LIFE: Third in a three-day series

Figuring out how to make immense ultra-lightweight space structures is a goal shared by UA astronomers and engineers in NASA's new Gossamer Spacecraft Initiative.

The space agency hopes to develop a set of technologies that will allow it to affordably launch huge, lightweight space telescopes, ``solar sails'' to propel probes to the edge of the solar system using the pressure of sunlight, and solar collectors to gather sunlight and beam it down to Earth for electrical use.

Such missions are more than a decade away. But Gossamer engineers received $6 million this year to start thinking about solutions, and the program will begin funding outside researchers soon.

``If you look up the word gossamer in the dictionary, you'll see a definition of something that's tenuous and insubstantial, like a spider web,'' said Chris Moore, Gossamer program manager.

``Our overriding goal is to reduce costs by going to very lightweight structures,'' he said. ``If we take a look at what we can do today or what we think we can do within the next 10 years, we realize that that technology is just not going to work.

``If we constructed these structures out of conventional materials, they would weigh hundreds and hundreds of tons, and there's no rocket that can launch a spacecraft that weighs that much,'' Moore said.

``It's probably going to require a major breakthrough.''

Moore and several University of Arizona astronomers were among 80 or so scientists and engineers who gathered in Tucson in January to brainstorm. At the Gossamer Optics Workshop, the focus was designs for giant space telescopes.

Most of the suggested approaches would use huge sheets of reflective plastic or foil stretched across circular or hexagonal frames to create reflectors resembling giant trampolines.

But other far-out ideas were tossed around, too. One scientist proposed a spinning plastic magnifying glass up to 50 yards across. Starlight would bend as it passed through the clear membrane, and a second spacecraft would collect the image from the focal point.

Another researcher said the shape of a thin space mirror could be controlled by blasting it with a beam of particles from an electron gun.

Membranous mirrors could be folded during launch to save space, then unfurled in orbit like a beach umbrella or an accordion. Alternatively, many small circular or hexagonal mirrors could be stacked like poker chips during launch, then pieced together into a giant mosaic mirror in space.

Mosaic mirrors with hundreds of segments might someday be used to image Earth-like planets around other s27tars, said Moore, who works at NASA's Langley Research Center in Hampton, Va.

But taking a picture of another Earth is the toughest challenge in space optics, and it won't happen any time soon, he said.

``To actually image their surfaces - we don't know how far away that's going to be,'' Moore said.

``Maybe it's 50 years from now. Maybe it's 100 years from now. Maybe it's not even possible.''

Graphic by Warren Huskey, The Arizona Daily Star: Canceling or 'nulling' starlight