In late 1970, the US military launched the first of a series of satellites to detect missile attacks. Until last month, two of these satellites remained operational in geosynchronous orbit, but their long-running mission has finally come to an end.
The US Space Force recently announced the retirement of the Defense Support Program (DSP), a constellation of satellites that once served as a crucial warning system during the Cold War. The last two remaining satellites were moved to a higher orbit in September ahead of their planned system shutdown.
Looking from above
Located 22,300 miles (35,888 kilometers) above the Earth, the DSP satellites were an important part of the US missile warning system. Each satellite was equipped with infrared detectors to detect intense heat and thermal signatures of rocket plumes against the Earth’s background.
The network of classified satellites spun continuously, scanning the Earth’s surface about six times every minute. At the time, infrared observation technology was still in its infancy, and the program helped transform it into an operational line of defense.
The US military initially developed the program in response to the growing threat of Soviet nuclear ballistic missiles. After the Cold War ended, DSP satellites were used in conventional warfare, such as the detection of Iraqi Scud missile launches during Operation Desert Storm in 1990-1991.
The satellite’s infrared sensors have also been used to identify early warning signs of natural disasters such as volcanic eruptions and forest fires.
The end of DSP
The US Air Force launched a total of 23 satellites for the DSP constellation from 1971 to 2007. Each of the satellites was equipped with additional capabilities and longer operating time.
The first batch of satellites each weighed about 2,000 pounds (907 kilograms) and carried 2,000 infrared detectors, while the final satellite was much heavier at 5,250 pounds (2,381 kilograms) with 6,000 detectors. The operating life of the satellites has also increased from just one year to more than 12 years.
Over time, however, the technology behind DSP was no longer cutting edge. Instead, the military began developing new-generation infrared satellites such as the Space Based Infrared System, which began operating in 2011, and the Next-Generation Overhead Persistent Infrared satellites, which may launch next year.
“These last two satellites were the culmination of over half a century of space-based early warning,” said US Space Force Col. Brandon Davenport in a statement. “The DSP constellation provided deterrence during the Cold War and protected our deployed warfighters from the Gulf War until their retirement last month.”