A few Air Force Academy researchers hope to take their latest invention where few have gone before — to near-Earth orbit.
They took a major step in getting there recently, testing a new type of telescope in zero gravity. Once the telescope is deployed, in 2015, it will be the first space-based membrane telescope.
Called the photon sieve, the invention allows a larger telescope on smaller satellites, with the potential to improve image quality.
It works like this: A thin plastic membrane is used instead of the glass normally found in the optics of a telescope, allowing the telescope to be folded into a satellite’s cargo bay. Once the satellite is in orbit, it’s deployed.
“The size of the telescope is determined by the size of the cargo bay,” said Dr. Geoff McHarg, a physics professor and director of the Academy’s space physics and atmospheric research center.
“The Hubble is only the size it is because that’s what would fit inside the space shuttle. NASA would have made a larger Hubble if they would have had a larger spacecraft to launch it. Imagine if you could get larger telescopes on smaller satellites — you’d have much better images.”
McHarg and fellow physics professor Dr. Michael Dearborn have been working on the project for a couple of years. 2nd Lt. Samantha Latch and Cadet Heather Nelson have also been involved with the laboratory work.
The group created a flat membrane to replace traditional glass optics.
“The photon sieve is thin membrane — much like plastic wrap used in a kitchen — with billions of tiny holes, each of which causes diffraction,” he said. “The holes are cleverly arranged to add up correctly to make an image. The photon sieve can be rolled delicately into a small space and stowed into a little spacecraft. “
The project has several practical applications for the Department of Defense and NASA. A larger telescope can provide better images of the earth, planets and the sun, McHarg said.
“The larger the optics, the better the image,” he said. “The photon sieve allows for larger optics, but on smaller satellites. And it’s less expensive to launch a smaller satellite — about $50,000 a kilogram.”
That project took them out of the USAFA labs and on a plane ride in Houston to the NASA Reduced Gravity Research Program.
There, the group boarded a Boeing 727, which flew a series of parabolic arcs that produce periods of weightlessness at the top of the flight arc for 20 seconds at a time. The time was short, but it was enough to test the deployment system of the telescope.
“It was unbelievable,” Nelson said. “Hard to explain what zero gravity feels like. They had us lying on the floor, and you just somehow started floating. It didn’t feel like anything else in the world. Suddenly, you didn’t weigh anything.”
McHarg, on the other hand, says the zero-gravity feeling is easy to explain.
“The plane is flying parabolic arcs,” he said. “At the top of the arc, you’re essentially in free fall. So it’s like free-falling in a parachute, except there’s no wind, because you’re still inside the plane.”
The tests were successful, Nelson said.
“It was beautiful,” she said. “The deployment was exactly like what we thought it would go. Now we know it will work in space.”
The deployment mechanism pops the telescope out very quickly — about two seconds — just “like a jack-in-the-box.”
“It doesn’t make the spacecraft tumble when it pops out,” he said. “So that was a positive experiment. We have a few technical things to work on, but overall, it was a huge success.”
While the photon sieve has been tested in the lab, it was the first time in zero-gravity. The next step for the team will be designing a photon sieve that will be put on a test satellite and observing what happens from there. The 2015 launch is scheduled on Falcon satellite 7.
The satellite will be much smaller than usual, McHarg said.
“It’s about 30 centimeters in depth and 10 centimeters in length,” he said, “about the size of a milk carton.”
And, unlike other satellites launched by the Air Force Academy, this one isn’t made by cadets. Instead, it’s created by Boeing specifically to test the photon sieve.
But the space tests wouldn’t be possible without the zero-gravity flights, McHarg said.
“The micro gravity flights were made possible to the Air Force’s space test program,” he said. “I have to say that, because without them, it wouldn’t have happened. These tests demonstrated that the basic deployment mechanism will work in a reduced gravity environment and doesn’t become fouled in the process.”