Table: Sensors in the Sky
A key ingredient in President Bush's missile-defense program is a satellite system called Space-Based Infra-Red System High. Technically ambitious and overbudget, this complex network of birds is designed to watch for rocket launches and identify missiles, using the following elements:
Defense support program is the existing early-warning satellite system--which uses 30-year-old technology.
Four new geostationary earth-orbit satellites are designed to provide better warnings of launches, more data about a rocket's probable target, info about short-range missiles such as Scuds, and intelligence for spy agencies.
Satellites in highly elliptical orbits would linger longer over the polar regions, providing superior data about northern Russia and China, for example.
A constellation of low-earth-orbit satellites will be the centerpiece of a complementary program called SBIRS Low, designed to distinguish real warheads from decoys.
Signals from all the birds are sent or relayed to a consolidated ground station facility in Colorado, or relocatable terminals--essentially satellite dishes on a truck bed or in a van.