Space Surveillance Telescope

The discovery and tracking of space debris is noted as a growing problem in the 21st century.

A computer-generated image representing space debris as could be seen from high Earth orbit. The two main debris fields are the ring of objects in geosynchronous Earth orbit (GEO) and the cloud of objects in low Earth orbit (LEO).

One problem is that among the 20-30 thousand large objects in orbit that are tracked, and an estimated 100 million debris as small as paint flecks, it is difficult to find objects that are harder to track than the big objects, but big enough to be harder to shield against if they collide with a space asset.[9] Even paint flecks are known to cause damage because of the extreme speeds at which objects travel in orbit.[9] In other words, there are objects too big to easily shield against, but too small to track.[9] Another concern is the Kessler syndrome, a chain reaction of collisions, creating far more space debris dangerous for working satellites.[10] Another concern are near-Earth asteroids, and the SST can detect these objects as part of its mission.[11]

Space Surveillance Telescope. DARPA.

The Space Surveillance Telescope program (SST) was DARPA's ground-based, advanced, optical system for detection and tracking of faint objects in space such as asteroids. It is also to be employed for space defense missions. The program is designed to advance, or expand, space situational awareness, and be able to quickly provide wide area search capability.

The SST is notable in the number of observations it makes and is currently listed by the Minor Planet Center as the world record holder for making the most observations in a single year. In its peak year so far (2015) it made a record 6.97 million observations, significantly more than any other telescope, including Pan-STARRS which is currently in second place, having recorded 5.25 million observations in its best year so far (2014).[12]

The green telescope with a clock drive can stay fixed on the same point of the Sky while Earth rotates, but the SST, like the red telescope, is not driven and so suffers from image streaking if the exposure duration is too long

The large curved focal surface array sensors are considered to be an innovative design. It encompasses improvements in detection sensitivity, has short focal length, wide field of view, and improvements in step-and-settle abilities. [note 1]

SST detects, tracks, and can discern small, obscure objects, in deep space with a "wide field of view system". It is a single telescope with the dual abilities. First the telescope is sensitive enough to allow for detection, also, of small, dimly lit objects (low reflectivity). Second it is capable of quickly searching the visible sky. This combination is a difficult achievement in a single telescope design.[13][14]

It is a Mersenne-Schmidt design with an F/1.0 aperture and a 3.5 meter primary mirror. It uses an array of charge-coupled device (CCD) sensors, arranged on a curved focal plane array. The SST mount uses an advanced servo-control technology, that makes it one of the quickest and most agile telescopes of its size. It has a field of view of 6 square degrees and can scan the visible sky in 6 clear nights down to apparent magnitude 20.5. These features allow the system to conduct multiple searches throughout the night, including the entire geostationary belt within its field. Unusually it does not have a field rotator and so is not able to track the movement of the sky as the Earth rotates. For this reason exposure times are limited to 2–3 seconds to prevent streaking due to movement of the sky during the exposure.[15]

As a telescope system, it can give precise locations of discovered objects, extrapolate the course of the object, and indicate the objects stability.[13][14][16]

The US Air Force ultimately took over the program and integrated the SST as a sensor in the Space Surveillance Network of the Air Force Space Command in 2009.[13][14]

The SST was initially deployed for testing and evaluation at the White Sands Missile Range in New Mexico. On December 6, 2013, it was announced that the telescope system would be moved to the Naval Communication Station Harold E. Holt in Exmouth, Western Australia, as part of the Australia-U.S. Space Situational Awareness Initiative. From there it will able to observe the Southern Celestial Hemisphere and collect data for the US Space Surveillance Network. The SST system was originally expected to be operational in 2016, but was not moved until 2017. As of 1 October 2017, satellite imagery of its site at 21.8957° S, 114.0899° E, showed only partial completion of the installation.[16] Due to the new site being in a cyclone region, construction has been delayed.[17]

• United States Space Surveillance Network
• List of largest optical reflecting telescopes
• List of largest optical telescopes in the continental United States
• Space debris
• Asteroid impact prediction

• Asteroid Detection with the Space Surveillance Telescope