to absorb the SBIRS Low constellation in its very early stages of development and renamed the program the Space Tracking and Surveillance System (STSS). This transition changed the direction of the program somewhat, but the overall mission remained the same — detection and tracking of ballistic missiles through all phases of flight. References External links Space-Based Infrared System Low at Risk of Missing Initial Deployment Date, U.S. General Accounting Office, February 2001 Fact Sheets: Space Based Infrared Systems: Space Based Infrared Systems Tactical Ballistic Missile Warning, U.S. Strategic Command Reconnaissance satellites of the United States Missile defense Infrared technology Early warning systems Military space program of the United States Military satellites Equipment of the United States Space Force Early warning satellites Spacecraft launched by Atlas rockets Military equipment introduced in the 2000s