Defense Support Program
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The U.S. Air Force Space Command-operated Defense Support Program (DSP) satellites form the principle component of the United States Satellite Early Warning System (SEWS). In their 22,300 mile geosynchronous orbits, they use infrared imaging sensors to detect intense sources of heat caused by missile or spacecraft launch booster plumes and nuclear explosions. They are occasionally also known as Integrated Missile Early Warning System (IMEWS) satellites.
The satellites are equipped with television cameras and infrared sensors operating through a wide-angle Schmidt telescope which is offset from the main axis of the telescope by 7.5°. The satellite spins at 6 rpm, so the sensors scan a larger circle than their field of view. Over several scans a stationary heat source such as a forest fire or volcanic eruption may be discriminated from a rapidly moving one.
Typically, DSP satellites are launched on a Titan IV booster and inertial upper stage combination. However, one DSP satellite was launched using the space shuttle on mission STS-44 (Nov. 24, 1991). SEWS operates a constellation of five DSP satellites, three operational and two as standbys should one of the operational satellites fail. The standby satellites are normally the least recently launched.
The 21st Space Wing, with headquarters at Peterson Air Force Base, Colo., has units that operate DSP satellites and report warning information, via communications links, to the North American Aerospace Defense Command and U.S. Space Command early warning centers within Cheyenne Mountain, located near Colorado Springs, Colo. These centers immediately forward data to various agencies and areas of operations around the world. Air Force Materiel Command's SBIRS Program office at the Space and Missile Systems Center, Los Angeles AFB, Calif., is responsible for development and acquisition of the satellites.
History
The Defense Support Program replaced the 1960s space-based infrared Missile Defense Alarm System (MiDAS). The first successful launch of MiDAS was May 24, 1960 and there were twelve launches before the DSP program replaced it in 1966.
The first launch of a DSP satellite was on 6 November 1970, since when it has become the mainstay of the United States ballistic missile early warning system. For the last 30-odd years hey have provided an uninterrupted space-based early warning capability. The original DSP satellite weighed 2,000 pounds and had 400 watts of power, 2,000 detectors and a design life of 1.25 years. Throughout the life of the program, the satellite design has undergone numerous improvements to enhance reliability and capability. The weight grew to 5,250 pounds, the power to 1,275 watts, the number of detectors increased three-fold to 6,000 and the design life has been increased to a goal of five years.
The numerous improvement projects have enabled DSP to provide accurate, reliable data in the face of evolving missile threats. On-station sensor reliability has provided uninterrupted service well past their design lifetime. Recent technological improvements in sensor design include above-the-horizon capability for full hemispheric coverage and improved resolution. Increased on-board signal-processing capability improves clutter rejection. Enhanced reliability and survivability improvements were also incorporated.
The 23rd, and last DSP satellite is scheduled to be launched in March 2005, after which SEWS will be replaced by the Space-Based Infrared System (SBIRS). The project was originally to have had a life of 25 satellites, but the last two have been cancelled, mainly due to the reliability of their predecessors. Only one satellite, IMEWS-19, failed to achieve the correct orbit.
There were five major improvement programs prior to the current block:
- 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-I (DSP-Improved), 1989
The satellites' effectiveness was demonstrated during Desert Storm, when DSP detected the launch of Iraqi Scud missiles and provided warning to civilian populations and coalition forces in Israel and Saudi Arabia.
However it also provided the impetus for the development of a new ground processing system. This was introduced in 1995 and called the Attack and Launch Early Reporting to Theater (ALERT). It allowed the quicker reporting of missile launches detected by the DSP satellites, making them more useful in warning of short range ballistic missile launches. By correlating data from all DSP satellites simultaneously it also allows more accurate determination of the trajectory of the quicker-burning short range missiles as an aid to their interception.
More recently, there has been some effort put into using DSPs' infrared sensors as part of an early warning system for natural disasters like volcanic eruptions and forest fires.
General characteristics
- Primary mission: Strategic and tactical missile launch detection
- Contractor team: Northrop Grumman, formerly TRW and Aerojet Electronics Systems
- Weight: 5,250 lb (2,386 kg)
- Orbit altitude: 22,000 miles (35,888 km)
- Power plant: Solar arrays generate 1,485 watts
- Height: 32.8 ft (10 m) on orbit; 28 ft (8.5 m) at launch
- Diameter: 22 ft (6.7 m) on orbit; 13.7 ft (4.2 m) at launch
- Date first deployed: 1970
- Latest Satellite Block: Sats 18-23
- Unit Cost: $400 million
Source:
Some of the information in this article is taken from the Fact Sheet published by Air Force Space Command, Public Affairs Office; 150 Vandenburg St., Suite 1105; Peterson AFB, CO, April 2004