DARPA’s Space Surveillance Telescope: How It Works

The Defense Advanced Research Projects Agency,
or DARPA, has developed the Space Surveillance Telescope to enable much faster discovery
and tracking of previously unseen or hard-to-find small objects in orbit that could potentially
collide with satellites. From its mountaintop perch at White Sands
Missile Range in New Mexico, this revolutionary optical telescope—called SST for short—combines
several groundbreaking technologies that are helping redefine what telescopes can do. SST has moved space situational awareness
from seeing only a few large objects at a time through the equivalent of a drinking
straw, to a “windshield” view with 10,000 objects at a time, each as small as a softball. SST can search an area larger than the continental
United States in seconds and survey the entire geosynchronous belt within its field of view—one
quarter of the sky—multiple times in one night. SST has enabled these game-changing capabilities
by developing many technological firsts. For example, SST uses the most steeply curved
primary telescope mirror ever made. This mirror enables SST to collect more light
to see images across a wider field of view than any other space surveillance telescope. SST can see 10 times fainter objects in GEO—geosynchronous
orbit, 22,000 miles above the Earth’s surface—than traditional telescopes. SST has the power to track small objects at
greater distances than other telescopes in the U.S. Space Surveillance Network that the
Air Force operates. SST has added to our knowledge of space debris
in GEO and has even tracked asteroids beyond the moon. To hold this mirror, SST uses an innovative
Mersenne-Schmidt design, which enables much more compact construction than traditional
telescopes. In fact, SST is the largest telescope ever
to use this design, which has also made it the quickest and most nimble large telescope
in the world. SST’s highly agile mount can rotate and
tilt at 17 degrees per second to rapidly follow space objects. The telescope weighs in at 90 tons and its
engines put out 38,000 foot-pounds of torque but are only as loud in combination as a microwave oven. SST’s camera includes its own noteworthy
inventions. SST developed the first-ever curved charge-coupled
device, or CCD, to provide clear imagery across its wide field of view because traditional
digital cameras with flat CCDs are unable to record images from such highly curved mirrors
without distortion. SST has the fastest telescope camera shutter
in the world and is able to take thousands of pictures a night. With these capabilities, SST offers unprecedentedly
rapid search of small, faint objects in space. It can collect up to 1 terabyte of data each
night and uses custom algorithms to shorten data processing timelines and provide same-day
observations to the Air Force. SST’s wide-open eye on the sky sees not
just around the Earth but also in the solar system and universe beyond. NASA is already leveraging SST’s capabilities
to see very faint objects in a wide field of view to help provide warning of asteroids
and other near-Earth objects. With 2.2 million asteroid observations in
2014, 7.2 million in 2015, and hopes for 10 million in 2016, SST has become the most prolific
tool for asteroid observation in the world. SST has also discovered 3,600 new asteroids
and 69 near-Earth objects, including four that carry a risk of possibly hitting the
Earth. The U.S. Air Force—the historical steward
of U.S. space situational awareness—is now poised to take ownership of SST and has announced
plans to operate it in Australia jointly with the Australian government. As SST prepares for its move, DARPA is upgrading
it to make it even more effective. In July 2016, DARPA installed an improved camera
that with an even wider field of view and increased sensitivity; this camera is designed
to increase by up to 50 percent the number of complete scans of the GEO belt SST can
perform each night. DARPA is enhancing SST’s faint-object detection
algorithms to compensate for the thicker atmosphere and hotter, wetter climate at SST’s new
home. DARPA is also providing faster search capability
for the U.S. military’s space surveillance community and same-night follow-up of near-Earth
asteroid candidates. SST’s numerous technological breakthroughs
and their potential to help augment space situational awareness capabilities both in
the United States and Australia represent another success in DARPA’s pursuit of its
singular and enduring mission: to make pivotal investments in breakthrough technologies for national security.

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