The Space Tracking and Surveillance System (STSS) (formerly SBIRS-Low) was a pair of satellites developed by the United States Missile Defense Agency (MDA) to research the space-based detection and tracking of ballistic missiles. Data from STSS satellites could allow interceptors to engage incoming missiles earlier in flight than would be possible with other missile detection systems. The STSS program began in 2001, when the "SBIRS Low" program was transferred to MDA from the United States Air Force. In December 2002, SBIRS Low Research & Development (SBIRS Low R&D) was renamed Space Tracking and Surveillance System (STSS). Launch One of the two satellites had been shipped to Cape Canaveral (CCAFS) on 4 May 2009; the second satellite arrived at the launch site on 25 June 2009. Two demonstration satellites were launched together on a single Delta II launch vehicle. Launch took place 25 September 2009, from Cape Canaveral Space Launch Complex 17 (LC-17B). STSS constellation consists of two satellites orbiting at 1350 km, 58.0° inclination, with 120 minute period. It was reported that several items of debris, identified by amateur satellite watchers as remnants of the Delta-2 launch vehicle, had crashed in a field in Mongolia on 19 February 2010. Early detection The perceived advantage of STSS was that its satellites, by operating at a lower altitude and by using long- and short-wave infrared sensors, would be able to acquire and track missiles in midcourse and during the boost phase. The role of STSS STSS was designed to be the low Earth orbiter (LEO) within the layered Ballistic Missile Defense System. It complemented the geosynchronous Defense Support Program, the Space-Based Infrared System, and other overhead non-imaging infrared (ONIR) systems and provided tracking cues to systems on the surface. The STSS program was developed in phases, the first of which was the launch of two demonstrator satellites. The demonstrators performed experiments and proved out systems and processes to establish a knowledge base for future operational designs. The demonstration satellites, built by Northrop Grumman Space Technology (spacecraft) and Raytheon Technologies (sensors) detected and tracked a two-stage Ground-Based Interceptor (GBI) during a U.S. Missile Defense Agency flight test on 6 June 2010. Congressional testimony According to Congressional testimony, military officials believed that STSS had the potential to bolster the nation's missile defense system. "Two recent flight tests demonstrated that STSS dramatically improved the precision of threat missile attacks and provided more accurate fire control