The Precision Tracking Space System (PTSS), currently being designed by the Missile Defense Agency (MDA), is intended to be a constellation of low-Earth-orbit satellites that track enemy ballistic missiles and distinguish enemy warheads from decoys (a process known as discrimination). The newest in a set of evolving concepts for missile defense that relies on satellite-based infrared tracking, the program supersedes the Space Tracking and Surveillance System (STSS) program. The design of PTSS will draw on knowledge gained from two STSS demonstration satellites, which were launched in September 2009 and are gathering data that will be used to assess the performance of onboard sensors. Existing plans call for one or more PTSS prototypes to be fielded initially, followed shortly by an operational constellation of 6 to 12 satellites.
This option would terminate the PTSS program. To estimate the savings from ending the program, the Congressional Budget Office assumed that the operational constellation would consist of 9 satellites, with the first to be launched in about 2019. Estimated savings would be about $1 billion over the next five years and about $7.5 billion over a decade. The 10-year savings would be realized by not starting research and development for the new satellites (about $2.5 billion) and by not buying, launching, and operating them (almost $5 billion). CBO's estimates do not include any savings that might arise from not building and launching replacement satellites after the initial constellation reached the end of its design life. (Construction of replacement satellites would begin within the next decade if the design life of the PTSS satellite was less than seven years.)
An argument in favor of this option is that the feasibility of operating infrared sensors in space for the purposes of discrimination has not yet been established. Another argument is that the constellation might not provide enough added value to justify the cost because programs that MDA and the Air Force plan to operate simultaneously with the PTSS also would provide some ability to track and discriminate enemy warheads. MDA has recently developed and fielded deployable surface-based radars for missile defense, including the Sea-Based X-Band (SBX) and the AN/TPY-2 radar systems, and has upgraded several early-warning radars to enhance the nation's ability to track ballistic missiles. MDA's plans to deploy surface-based radar close to Iran and North Korea will provide tracking and discrimination information much earlier in the flight of ballistic missiles from those countries than have previous approaches. MDA has also begun research into using infrared sensors onboard unmanned aerial vehicles to track ballistic missiles. In addition, the Air Force is improving its missile-warning capability with the Space-Based Infrared System (SBIRS)High constellation--satellites in highly elliptical orbits are currently in operation, and the first launch of a SBIRS-High GEO (geosynchronous) satellite is planned for 2011. The sensors on those satellites will also be able to track ballistic missiles early in their flight.
An argument against this option is that the data being gathered from the STSS demonstration satellites might show that space-based infrared sensors would be effective and valuable for tracking and discriminating warheads launched on enemy ballistic missiles. Reliance on a combination of ground-based radars and airborne infrared systems would probably not match the broad geographic coverage offered by a full constellation of PTSS satellites and thus would reduce the nation's ability to track ballistic missiles through all phases of flight for some missile trajectories. The PTSS may also have greater capability to track missile salvos--multiple missiles launched nearly simultaneously--than those other systems.