An evolving series of satellites built by the United States to detect intercontinental ballistic missiles on launch. After forty years of service, they had grown from 900 kg to 2380 kg in mass, and gone from being capable of detecting ICBM launches to detecting and tracking tactical ballistic missiles, but followed the same operating principle and layout.

The Defense Support Program (DSP) constellation consisted of four spacecraft spaced around the earth in geosynchronous orbit plus one in-orbit spare that could be repositioned as needed. These spacecraft were initially designed to provide warning-at-launch of an intercontinental ballistic missile attack by the Soviet Union. This would provide additional minutes of warning compared to early warning radars, that could only detect missiles as they came 'over the horizon' and were easily disabled in the first stage of an attack. It also eliminated the advantage of the Soviet's fractional orbital bombing system R-36-O missiles, which placed warheads in orbit, allowing them to come 'under the radar' or from approach angles not covered by the early warning radars. It also provided warning of submarine-launched missiles, which could be launched from locations with inadequate radar coverage.

Such attacks never materialized, although the DSP's may have contributed to the Soviet decision to sharply limit R-36-O deployment to token levels. However the DSP's instead provided intelligence on nearly every medium- and long-range ballistic missile launch since being put in service, including the hundreds of Scud launches during the Iran-Iraq 'War of the Cities' in 1985-1986. They proved able to detect static tests of rocket engines on the earth's surface, as well as the exhaust plumes of military aircraft in afterburner. During America's long involvement with Iraq, they provided early warning of tactical ballistic missile launches against American or Allied targets, allowing shelter to be taken and Patriot missile defenses to be readied for the incoming missiles. When Chinese ballistic missile testing surged to a rate of one per week in 2006-2007, DSP was able to keep track of the activity.

Each satellite spent a month after launch in positioning, test, and systems initialization and calibration before being handed over to the USAF operational command. DSP's were controlled by the USAF from Falcon (later Schriever) AFB near Colorado Springs until 2007, when control transitioned to the new SBIRS Control Station in Aurora, Colorado.

The spacecraft were designed for a 3-5 year operational life, but this was extended to 10 to 15 years through careful fuel, power, and infrared temperature management techniques. The result was that by 2006 as many as 10 DSP's were still functioning, allowing two or three satellites to observe a single launch. This allowed for stereo views of launches and better plume characterization. The only DSP satellite to fail in service completely was DSP-19, which had a hydrazine propellant line rupture. But his spacecraft had endured extraordinary stresses during ascent aboard a malfunctioning IUS upper stage, which left it stranded in geosynchronous transfer orbit. Even this satellite proved useful. Since it transited the van Allen radiation belts twice daily, it allowed the USAF to assess the effect of an extreme radiation environment on DSP electronics.

As of 2007 it was planned that the new SBIRS satellite constellation would take over the prime missile warning function from DSP by the end of 2012. However the DSP's would be kept in service as back-ups and gap-fillers, with the belief that DSP-22 and -23 would remain in service until 2017-2022.

DSP satellites were built in a series of models of ever-increasing sophistication, weight, and capability:

• Phase I - the original model, for ICBM detection, was equipped with a 2000 pixel array. At the time they were often referred to as IMEWS (Integrated Missile Early Warning Satellites). Designed for launch by the Titan 3C, and used the booster's maneuverable Transtage to take the satellites to geostationary orbit. Mass of these models was 900 kg. The spacecraft was zero-momentum stabilized using a reaction wheel to counter the spacecraft spin. Body mounted cells and deployable panels generated 400 W. The payload included a 3.6 m Schmidt telescope with 2000 element infrared sensor, and separate nuclear detection sensors. The 15 month design life was vastly exceeded; instead reaching 7 to 12 years. The first four satellites launched were of this model, and made up the first DSP constellation.
• Phase II - these satellites had an extended 24-month design lifetime and a mass of 1040 kg. Power was increased to 680 W. Satellites 7 through 9 were of this model, and actual lifetime was seven to nine years. This was the second DSP constellation.
• Multi-Orbit Satellite/Performance Improvement satellites had a 36-month design life, and were designed to function in either geosynchronous or Molniya orbits (the latter to give coverage of submarine-launched-ballistic missile launches from the Arctic). They also had increased hardening against attack by blinding lasers, and improved detector arrays. Satellites 10 to 13 were of this model, with a mass of 1170 kg. Actual lifetime was 11 to 18 years. There were no acknowledged launch of this satellite types in the Molniya-type orbits; perhaps such launches were made covertly and were classified as communications or ELINT satellites by external observers. The four MOS/PIM satellites made up the third DSP constellation.
• Phase II Upgrade - Satellites 5 and 6, which were Phase II reserve satellites and had not been launched, were retrofitted for a 36-month design life, and equipped with the 6,000 detector array developed for the DSP-1 block 14 satellites, which provided enhanced capabilities for raid resolution and polar/global coverage. They were flown on missions 12 and 13, total mass 1670 kg. Perhaps these were rushed into service due to delays in development of the DSP-1.
• DSP-1 - Satellites 14 to 23 were significantly enlarged for a five-year design life, and increased survivability against countermeasures. They included the 6,000 pixel array, and were built in two series - Block 14 and Block 18. They had a launch mass of 2380 kg. Cost of the final satellite was $400 million.

All DSP's were equipped with dual radiation detectors designed to detect neutrons, gamma-, and x-rays produced by nuclear explosions in the atmosphere or space. These replaced the separate Vela satellites launched in the sixties. Beginning with DSP-23, these were supplemented by a 24-kg Space Atmosphere Burst Reporting System (SABRS), which would be used on the SBIRS-GEO satellites that would replace DSP.

It had been planned in the 1980's to equip the DSP's with a laser data cross-link produced by McDonnell-Douglas. This however was cancelled after its development cost ran vastly over budget.

Design Life: 3 years (5 year goal). Typical orbit: Geosynchronous. Length: 10.00 m (32.00 ft). Maximum Diameter: 4.00 m (13.10 ft). Mass: 2,358 kg (5,198 lb). Electrical System: Solar panels, on cylinder-body and flap extensions. Electric System: 1.30 average kW. Associated Launch Vehicle: Titan 34D, Titan 3C, Shuttle, Titan 4, Titan 4B.

• 1970 November 6 - IMEWS 1 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. FAILURE: Partial Failure. Mass: 900 kg (1,980 lb). Perigee: 25,840 km (16,050 mi). Apogee: 36,128 km (22,448 mi). Inclination: 16.40 deg. Period: 1,197.90 min.

  First generation geosynchronous ballistic missile launch detection satellite; placed in incorrect subsynchronous orbit. One account claimed that it exhausted its propellant before it could be put into operation, but a 2007service history chart showed that is was considered operational for three years, well beyond its planned life.

• 1971 May 5 - IMEWS 2 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. Mass: 900 kg (1,980 lb). Perigee: 36,156 km (22,466 mi). Apogee: 36,527 km (22,696 mi). Inclination: 10.50 deg. Period: 1,464.60 min.

  First generation geosynchronous ballistic missile launch detection satellite. First completely sucessful operational satellite, remained in service for nearly 12 years. Positioned over the Indian Ocean at 75 deg E in 1979-1982. As of 1983 May 11 located at 73.28W drifting at 7.684W degrees per day.

• 1972 March 1 - IMEWS 3 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. Mass: 900 kg (1,980 lb). Perigee: 35,416 km (22,006 mi). Apogee: 35,962 km (22,345 mi). Inclination: 0.20 deg. Period: 1,429.90 min.

  First generation geosynchronous ballistic missile launch detection satellite, remained in service for over nine years. Positioned over the Pacific Ocean at 165 deg E in 1979-1980. As of 2003 Mar 5 located at 74.63E drifting at 0.712W degrees per day.

• 1973 June 12 - IMEWS 4 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. Mass: 900 kg (1,980 lb). Perigee: 35,777 km (22,230 mi). Apogee: 35,786 km (22,236 mi). Inclination: 0.30 deg. Period: 1,435.90 min.

  First generation geosynchronous ballistic missile launch detection satellite, remained in service for over seven years. Positioned in geosynchronous orbit over the Indian Ocean at 75E in 1973; over the Americas at 105 deg W in 1979-1980. As of 1983 Jan 3 located at 73.21W drifting at 1.648W degrees per day.

• 1975 December 14 - IMEWS 5 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. Mass: 1,040 kg (2,290 lb). Perigee: 35,671 km (22,164 mi). Apogee: 35,785 km (22,235 mi). Inclination: 3.00 deg. Period: 1,436.00 min.

  Second generation geosynchronous ballistic missile launch detection satellite, remained in service for over twelve years. As of 1982 Dec 16 located at 34.61E drifting at 0.823E degrees per day.

• 1976 June 26 - IMEWS 6 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. Mass: 1,040 kg (2,290 lb). Perigee: 35,620 km (22,130 mi). Apogee: 35,860 km (22,280 mi). Inclination: 0.50 deg. Period: 1,433.30 min.

  Second generation geosynchronous ballistic missile launch detection satellite, remained in service for over eight years. Positioned over the Atlantic Ocean from 1976 to 1981: at 35 deg W in 1976-1977; at 65 deg W in 1977-1979; and 35 deg W in 1979-1980; and 65 deg W in 1980-1981. Then moved over the Pacific Ocean at 125 deg W, then 140 deg W in 1981-1982; then over the Indian Ocean at 75 deg E in 1982-1984.

• 1977 February 6 - IMEWS 7 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. Mass: 1,040 kg (2,290 lb). Perigee: 35,620 km (22,130 mi). Apogee: 35,860 km (22,280 mi). Inclination: 0.50 deg. Period: 1,433.30 min.

  Second generation geosynchronous ballistic missile launch detection satellite, remained in service for nearly seven years. Positioned in geosynchronous orbit over the Pacific Ocean at 135 deg W in 1977-1979; over the Indian Ocean 70 deg E in 1979-1984.

• 1979 June 10 - IMEWS 10 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. Mass: 1,170 kg (2,570 lb). Perigee: 35,712 km (22,190 mi). Apogee: 35,854 km (22,278 mi). Inclination: 1.80 deg. Period: 1,435.90 min.

  First Multi-Orbit Satellite / Performance Improvement ballistic missile launch detection satellite, remained in service for nearly six years. Positioned in geosynchronous orbit over the Pacific Ocean at 135 deg W in 1979-1982; 85 deg W in 1982-1984; 135 deg W in 1984; 125 deg W in 1985..

• 1981 March 16 - IMEWS 11 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. Mass: 1,170 kg (2,570 lb). Perigee: 35,463 km (22,035 mi). Apogee: 35,527 km (22,075 mi). Inclination: 2.00 deg. Period: 1,421.20 min.

  Multi-Orbit Satellite / Performance Improvement ballistic missile launch detection satellite, remained in service for nearly eleven years. Positioned in geosynchronous orbit over the Pacific Ocean at 69 deg W in 1981-1982; 135 deg W in 1982-1984; 75 deg E in 1984-1985. As of 2003 Mar 6 located at 40.27E drifting at 0.598E degrees per day.

• 1982 March 6 - IMEWS 13 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 3C. Mass: 1,170 kg (2,570 lb). Perigee: 35,520 km (22,070 mi). Apogee: 35,598 km (22,119 mi). Inclination: 2.00 deg. Period: 1,424.40 min.

  Multi-Orbit Satellite / Performance Improvement ballistic missile launch detection satellite, remained in service for over sixteen years. Positioned in geosynchronous orbit over the Pacific Ocean at 68 deg W in 1982; 35 deg W in 1983-1988; 165 deg W in 1988-1989; 35 deg W in 1989-1991.

• 1984 April 14 - DSP - Launch Site: Cape Canaveral. Launch Vehicle: Titan 34D. Mass: 1,170 kg (2,570 lb). Perigee: 35,530 km (22,070 mi). Apogee: 35,530 km (22,070 mi). Inclination: 1.30 deg. Period: 1,423.00 min.

  Multi-Orbit Satellite / Performance Improvement ballistic missile launch detection satellite, remained in service for nearly eighteen years. Positioned in geosynchronous orbit at 135 deg W in 1984-1985; 65 deg E in 1985-1988; as of 31 December 1990 at 99.16 deg W drifting at 0.050 deg W per day.

• 1984 December 22 - USA 7 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 34D. Mass: 1,670 kg (3,680 lb). Perigee: 35,619 km (22,132 mi). Apogee: 35,915 km (22,316 mi). Inclination: 3.40 deg. Period: 1,445.80 min.

  Reserve Phase 2 DSP ballistic missile launch detection satellite fitted with Block 14 sensors, remained in service for nearly eighteen years. Observed Scud launches during Gulf War. Positioned in geosynchronous orbit at 155 deg W in 1985-1988; 65 deg E in 1988-1991; 145 deg E in 1991-1992; 105 deg E in 1992-1993; 5 deg E in 1993-1994.

• 1987 November 29 - USA 28 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 34D. Mass: 1,670 kg (3,680 lb). Perigee: 35,514 km (22,067 mi). Apogee: 35,558 km (22,094 mi). Inclination: 2.90 deg. Period: 1,423.30 min.

  Reserve DSP ballistic missile launch detection satellite fitted with Block 14 sensors, remained in service for only five years.. Observed Scud launches during Gulf War. Positioned in geosynchronous orbit at 35 deg W in 1988-1989; 10 deg E in 1989-1992; 35 deg W in 1992-1993; 105 deg E in 1993; 165 deg W in 1999.

• 1989 June 14 - USA 39 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 4. Mass: 2,360 kg (5,200 lb). Perigee: 35,699 km (22,182 mi). Apogee: 35,614 km (22,129 mi). Inclination: 3.10 deg. Period: 1,421.80 min.

  First DSP-1 Block 14 ballistic missile launch detection satellite; first Titan 4 launch. Positioned in geosynchronous orbit at 165 deg W in 1990-1994; 145 deg W in 1999; 166 deg W in 2000.. Still in service as of March 2007. As of 2007 Feb 5 located at 145.23W drifting at 0.014W degrees per day.

• 1990 November 13 - USA 65 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 4. Mass: 2,360 kg (5,200 lb). Perigee: 35,614 km (22,129 mi). Apogee: 35,699 km (22,182 mi). Inclination: 3.10 deg. Period: 1,421.80 min.

  DSP-1 Block 14 ballistic missile launch detection satellite. Positioned in geosynchronous orbit at 105 deg E in 1991; 70 deg E in 1991-1992; 5 deg E in 1992-1993; 35 deg W in 1993; 38 deg W in 1999-2004. Believed to have been taken out of service in 2006.

• 1991 November 24 - USA 75 - Launch Site: Cape Canaveral. Launch Vehicle: Shuttle. Mass: 2,360 kg (5,200 lb). Perigee: 35,795 km (22,241 mi). Apogee: 35,787 km (22,236 mi). Inclination: 2.50 deg. Period: 1,421.90 min.

  DSP-1 Block 14 ballistic missile launch detection satellite, deployed from shuttle STS-44 on 25 November 1991. Only DSP launched from the shuttle before the Challenger disaster moved the payload to the Titan 4. Positioned in geosynchronous orbit at 130 deg W in 1992; 70 deg E in 1992; 8 deg E in 1999; 40 deg W in 2000. Still in service as of March 2007.

• 1994 December 22 - USA 107 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 4. Mass: 2,360 kg (5,200 lb). Perigee: 35,780 km (22,230 mi). Apogee: 35,790 km (22,230 mi). Inclination: 0.00 deg. Period: 1,436.10 min.

  DSP-1 Block 14 ballistic missile launch detection satellite. Positioned in geosynchronous orbit at 103 deg E in 1999. Still in service as of March 2007.

• 1997 February 23 - USA 130 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 4B. Mass: 2,380 kg (5,240 lb). Perigee: 35,780 km (22,230 mi). Apogee: 35,790 km (22,230 mi). Inclination: 0.00 deg.

  DSP-1 Block 14 ballistic missile launch detection satellite. Positioned in geosynchronous orbit at 70 deg E in 1999. Still in service as of March 2007.

• 1999 April 9 - USA 142 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 4B. FAILURE: IUS first and second stages failed to separate. Mass: 2,380 kg (5,240 lb). Perigee: 720 km (440 mi). Apogee: 35,800 km (22,200 mi). Inclination: 28.00 deg.

  The Titan 4B placed the IUS upper stages and DSP-1 Block 14 ballistic missile launch detection satellite. payload into a 188 km x 718 km x 28.6 deg parking orbit. The first stage of the IUS burned at 18:14 GMT and put the second stage and payload into a geosynchronous transfer orbit. The IUS second stage fired at 23:34 GMT in order to place the spacecraft in geosynchronous orbit. However, at least one connector remained attached between the stages, and the second stage motor nozzle did not extend properly. When the stage fired, the vehicle tumbled wildly during the burn. Separation of the DSP was achieved. Although it could not perform its primary mission, it did provide a good test case in that the effects of radiation on its systems could be monitored as they underwent twice-daily passages of the Van Allen Radiation Belts. However after some weeks the hydrazine propellant aboard the satellite vented into space due to a broken fuel line. It was believed this had been induced by the wild ride aboard the IUS-2 stage.

• 2000 May 8 - USA 149 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 4B. Mass: 2,380 kg (5,240 lb). Perigee: 35,780 km (22,230 mi). Apogee: 35,790 km (22,230 mi). Inclination: 0.00 deg.

  DSP-1 Block 14 ballistic missile launch detection satellite. Delivered by the two-stage IUS-22 solid rocket into geostationary orbit. Fullfilled mission of DSP 19 launched in 1999 into the wrong orbit when its IUS stage failed. Still in service as of March 2007. As of 2005 Apr 2 located at 8.05E drifting at 0.166E degrees per day.

• 2001 August 6 - USA 159 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 4B. Mass: 2,380 kg (5,240 lb). Perigee: 35,780 km (22,230 mi). Apogee: 35,780 km (22,230 mi). Inclination: 2.90 deg. Period: 1,435.76 min.

  Launch postponed from February, then delayed from July 27. USA 159 was a US Air Force Defense Support Program infrared missile early warning satellite was placed by the Titan core into a 328 x 663 km x 28.7 deg parking orbit. The Boeing IUS-16 upper stage then fired its first solid motor to enter geostationary transfer orbit. The second IUS solid motor fired at around 14:00 GMT placing DSP Flight 21 in near-geosynchronous orbit. Still in service as of March 2007.

• 2004 February 14 - USA 176 - Launch Site: Cape Canaveral. Launch Vehicle: Titan 4B. Mass: 2,380 kg (5,240 lb). Perigee: 35,852 km (22,277 mi). Apogee: 36,105 km (22,434 mi). Inclination: 0.68 deg. Period: 1,445.94 min.

  DSP-1 Block 14 ballistic missile launch detection satellite. Last flight of the IUS upper stage. Launch delayed from November 4, 2003, and January 17, 2003. Planned IMEX piggyback payload cancelled. Still in service as of March 2007, expected to remain operational until 2017-2022. As of 2004 Feb 15 located at 96.66W drifting at 2.464W degrees per day.

• JPL Mission and Spacecraft Library, Jet Propulsion Laboratory, 1997. Accessed at: http://msl.jpl.nasa.gov/home.html.

• USAF Satellite Database, USAF Institute of Technology, 1995. Accessed at: ftp://archive.afit.af.mil/pub/space/.

• McDowell, Jonathan, Jonathan's Space Home Page, Harvard University, 1997-present. Jonathan McDowell's complete on-line listing of all objects orbited and over 20,000 rocket launches Accessed at: http://www.planet4589.org/jsr.html.

• Krebs, Gunter, Gunter's Space Page, University of Frankfurt, 1996. Accessed at: http://www.skyrocket.de/space.

• Vis, Bert, Spaceflight, "Shuttle Weather Watch", 1996, Volume 38, page 170. Details on USAF weather astronauts

• McDowell, Jonathan, Jonathan's Space Report (Internet Newsletter), Harvard University, Weekly, 1989 to Present. Essential internet newsletter recording worldwide weekly space events. Accessed at: http://www.planet4589.org/jsr.html.