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In response to the evolving threats, DSP has undergone five major upgrades that allowed it to provide more accurate and reliable data to the warfighter. For example, the addition of a medium wavelength infrared capability has provided enhanced missile warning mission utility. This upgrade marked the first space sensor application of mercury cadmium telluride infrared sensors, the material of choice for today's infrared sensors. All of the DSP satellites were spinning satellites with the infrared sensor at the front end of the spacecraft. The DSP satellites orbit the earth approximately 22,000 miles over the equator. The current DSP spacecraft is more survivable than its predecessors, accommodates 6,000 detectors, uses approximately 1,275 watts of power, with an on-orbit weight of approximately 5,200 pounds at the beginning of life, including fuel.

- 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 - 2007, 10 satellites launched
- First launch on 6 November 1970
- Final launch on 10 November 2007

Current as of April 2015

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Today’s DSP-I (improved) weighs 5,200 pounds vs. just 2,000 pounds for the original versions, requires 1,275 watts of power vs. 400, uses 6,000 detectors vs. 2,000, and is approximately 33 feet long and 14 feet in diameter. Recent technological improvements in sensor design include above-the-horizon capability for full hemispheric coverage and improved resolution, as well as increased on-board signal-processing capability.

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The current Satellite Early Warning System (SEWS) consists of 5 DSP satellites; 3 provide frontline operational service, with 2 available as backups should problems emerge with the primary satellites.

The program’s lifetime has seen the launch of 23 DSP satellites, and improvements to DSP via 5 upgrade sets have allowed those satellites to exceed their design lifespan.

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But soon after [DSP] entered service Aerospace Corporation scientists began detecting other heat targets, including surface to air missiles and ground explosions. The company’s scientists and engineers also began unusual infrared events. These infrared returns occurred over Soviet territory at regular intervals and traveled in relatively straight lines. They were clearly not ballistic missiles. The engineers analyzing the heat sources soon determined that they were originating at Soviet bomber bases, notably those that fielded Backfire bombers.
[...]
In spring 1983 the Air Force approved a Navy project to take advantage of the DSP capability to detect these “walking dots.” It was code-named SLOW WALKER. Starting in 1985 the Navy deployed a regular contingent to Australia to extract the data from the DSP satellite transmissions and then manually disseminate the information to the fleet. This was called the SLOW WALKER Reporting System, or SLWRS. By the late 1980s the Navy improved its SLOW WALKER capability to the point where the information was disseminated nearly instantaneously.