The U.S. Air Force Space Command operates the Defense Support Program (DSP) satellites which are part of North America's early warning system. The DSP satellites detect missile launches, space launches and nuclear detonations. The satellites feed warning data, via communications links, to NORAD and U.S. Space Command early warning centers. These centers immediately forward data to various agencies and areas of operations around the world. DSP satellites use an infrared sensor to sense heat from missile and booster plumes against the earth's background.

The current DSP spacecraft is more survivable than its predecessors, with 6,000 detectors, generates 1.485 kW and uses 1.274 kW of power, and weighs 2386 kg (5260 lbm). The satellite, stowed, is 4.2 m (13.7 ft) in diameter and 8.5 m (28 ft) tall. Deployed it is 10 m (32.8 ft) in diameter and 6.7 m (22 ft) in height.

The satellite program has undergone five major design changes. These "blocks" of satellites are:

• Block 1: Phase I, 1970-1973, 4 satellites
• Block 2: Phase II, 1975-1977, 3 satellites
• Block 3: Multi-Orbit Satellite Performance Improvement Modification (MOS/PIM), 1979-1984, 4 satellites
• Block 4: Phase II Upgrade, 1984-1987, 2 satellites
• Block 5: DSP-1, 1989 - present

Each satellite costs approximately US$250 million

The U.S. Air Force Materiel Command's Space and Missile Systems Center at Los Angeles Air Force Base, Calif., is responsible for development and acquisition of DSP satellites. The satellite prime contractors are TRW and Aerojet. Members of the 50th Space Wing's 1st Space Operations Squadron and several 21st Space Wing units provide command and control support for the satellite.

DSP 22 is scheduled for launch on a Titan 402B, no earlier than 2003. DSP 23, the last spacecraft in the series, and is currently scheduled to fly on the second Boeing Delta 4H vehicle in late 2003. Lockheed Martin has proposed to launch the spacecraft on a commercial Atlas 5/551 vehicle if the Delta 4H is not ready in time. The U.S. Department of Defense is studying the possibility of launching the spacecraft onboard the space shuttle Columbia in case of additional delay in the availability of Evolved Expendable Launch Vehicles (EELVs), after the Lockheed Martin Titan 4B booster is no longer be available. Launching DSP 23 on a space shuttle would require the procurement of an additional Inertial Upper Stage (IUS) from Boeing, though the product line has been closed. Launching DSP 23 would require adapting an IUS stage built as a Titan 4B upper stage for its use on the space shuttle.