From: LARRY KLAES (ljk4_at_msn.com)
Date: Tue Dec 23 2003 - 06:58:18 PST
Just around the bend: a space mirror that folds
By Sue Vorenberg
Mazes of lenses, mirrors and strange optical illusions line the desktops of Dan Marker's and Mark Gruneisen's labs.
Hidden deep in these Air Force Research Laboratory labyrinths in Albuquerque is the technology to build the grandchild of the Hubble Space Telescope. When finished, it will weigh less and see more than its predecessors. Most important, it will be much lighter on taxpayers' wallets, the two scientists predict.
"The idea is to use these lightweight, rolled-up mirrors to make a telescope that is bigger than Hubble," Gruneisen said. "We couldn't do that before because the glass lenses of older telescopes - which are very heavy and completely rigid - couldn't be any larger than the bay of the space shuttle."
The telescope the two lab scientists are developing is about 10 times lighter than the lightest space telescope materials now. Shuttle payloads can cost upward of $10,000 per pound, and so lighter is significantly cheaper.
The two say they hope to have the first small lightweight space telescope made from the material in the next 10 years, soon after the launch of the second generation Hubble, called the James Webb Telescope.
The James Webb, named after NASA's second administrator, who died in 1992, is scheduled to launch in 2011. Its 21-foot mirror, which weighs about a third of the 7-foot Hubble mirror, must be launched in 18 segments and assembled in space.
The James Webb will cost about $824 million, including launch costs, its support structure and adaptors, according to the National Aeronautics and Space Administration Web site.
"That mirror is called ultralightweight," Marker said. "It weighs about 3 pounds per square foot. What we're doing is building a mirror that weighs 3 pounds per 10 square feet."
The lab's solution has been to build a telescope mirror out of plastic. A plastic mirror can be larger than the space shuttle bay and folded up, Marker said.
The trick has been to make something flexible and bendable that can also be used as a telescope mirror, he said.
"This isn't like a bathroom mirror," Marker said. "That's actually a very poor optical surface - it's bumpy, and the thickness varies throughout it. What we need for an optical quality mirror is a very flat surface - something that the bumps are smaller than 1/3,000th the thickness of a sheet of paper."
That thickness variation, 30 nanometers, is far smaller than that of a bathroom mirror, which typically has bumps bigger than 100,000 nanometers.
The lab couldn't find anybody who made a plastic like that, and so seven years ago it partnered with a private company, SRS Technologies in Alabama, and the two groups developed one on their own.
Until recently, the biggest mirror the two groups have been able to make was about 6 inches wide. In late August they made a technological breakthrough and built their first 3-foot mirror.
Eventually, they want to build a mirror that is 30 feet wide, Marker said
Another problem: The images collected with the plastic material are fuzzier than images from a glass mirror. The plastic material vibrates more easily and doesn't hold its shape quite as well as a glass mirror, Gruneisen said.
"If the shape isn't consistent, if there are aberrations, then the light from whatever we're looking at doesn't get to the telescope at the same time," Gruneisen explained. "That makes the image fuzzy."
To correct for that Gruneisen has created a high-tech optical filter made of liquid crystal - like that of a laptop computer screen - and electric current.
After light from a star or galaxy hits inconsistent or shaky parts of the telescope, it goes through Gruneisen's device, which looks sort of like a very long coffee can. The device can speed up or slow down the light so it all gets to the viewing screen of the telescope at the same time.
"Eventually we can use something like this for a lot more than just space science," Gruneisen said. "We can point it at the Earth to see objects on the ground. We may also, further down the line, be able to use it to transmit energy from one place to another. There are really quite a few things we can do when it's fully developed."
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