In order to dodge something, you need to see it. If that something is space debris then sometimes the best thing to use is an old-fashioned telescope – or, in the case of the US Department of Defense, a state-of-the-art telescope capable of searching an area larger than the United States in seconds. That’s why DARPA is preparing to deliver the new Space Surveillance Telescope (SST) to Western Australia, where it will help track small satellites and space debris orbiting the Earth when it becomes operational in 2016.
Orbital satellites have become vital for civilian and military applications, but setting up and maintaining the constellation of spacecraft around the Earth has also produced the dangers of space debris and general crowding. This has made keeping track of what is up there a top priority for the US Department of Defence, which hopes to avoid another incident like the 2009 collision of the Iridium 33 and Kosmos-2251 satellites.
The problem is that there's a lot of space out there and one of the most valuable strips of real estate, geosynchronous orbit, is a long way away at a distance of 22,000 mi (35,000 km). This is a bit too far for conventional telescopes with their narrow fields of view to track small objects, so DARPA was tasked with the development of a new ground-based, broad-area telescope for conducting searches to detect and track small objects in deep space.
The result is the Space Surveillance Telescope (SST). Under development since 2002, it’s a Mersenne-Schmidt design that provides wide fields of view with limited aberrations. Like telescopes of similar design, it has a concave paraboloidal primary mirror, a convex spherical secondary mirror, and a concave spherical tertiary mirror.
Where it differs is that the mirrors are among the steepest aspherical curvatures ever to be polished, with DARPA saying this allows the telescope to boast the fastest optics of this aperture class. In addition, the SST is the first telescope to be fitted with a large focal surface array of curved charge coupled devices (CCD) to capture images.
Put all that together with some advanced servo-control technology, and you have a telescope that has a short focal length, a wide field of view, is very compact, and can execute rapid step-and-settle motions, which DARPA says makes it one of the fastest and most agile telescopes of its size. According to the agency, the SST could detect the light of a laser pointer on the Empire State Building in New York from Miami, Florida – assuming you could drill a hole through the curve of the Earth.
The optics of the SST allow it to cover very large areas very quickly. DARPA says that it can scan the entire geosynchronous belt several times in one night, and can detect smaller, dimmer, more transient objects than previous telescopes. This means if can not only detect objects, but gather data for more rapid and accurate predictions of their orbits.
The SST is currently at the White Sands Missile Range in New Mexico for testing and evaluation. It’s scheduled to be moved to the Harold E Holt Naval Communication Station in Exmouth, Western Australia, where it will watch the sky of the Southern Hemisphere. Based on a Memorandum of Understanding signed on Nov. 20, DARPA will deliver the SST and the Australian government will build an enclosure for it and operate it after the transfer is completed in 2016.
Once in service, the SST will become part of the Space Surveillance Network (SSN), which is a US Air Force system that uses a global network of radar and optical telescopes to identify and catalog potentially hazardous objects for spacefaring nations. In addition, it will be used by astronomers to hunt for asteroids and supernovae.
“The SST has moved space situational awareness from looking through a drinking straw to a windshield view, where we can see 10,000 objects the size of a softball at a time — any of which could put satellites at risk,” says Lt Col Travis Blake, DARPA program manager. “This program has already helped revolutionize ground-based space surveillance technology. From its new location, it could greatly expand the capability of the United States, Australia and other nations to keep their space assets safe.”
The video below shows the SST undergoing testing.