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History of GPS Technology
BrowseNumber:9836;ReleaseDate:2013-07-12 09:18:27

A GPS satellite is a satellite used by the NAVSTAR Global Positioning System (GPS).

The first satellite in the system, Navstar 1, was launched February 22, 1978. The GPS satellite constellation is operated by the 50th Space Wing of the United States Air Force.
Block I satellites

A Navstar GPS satellite undergoing pre-launch testing.
Beginning with Navstar 1 in 1978, ten "Block I" GPS satellites were successfully launched. One satellite, "Navstar 7", was lost due to an unsuccessful launch on December 18, 1981.[1] The Block I satellites were launched from Vandenberg Air Force Base using Atlas rockets that were converted intercontinental ballistic missiles.
The satellites were built by Rockwell International at the same plant in Seal Beach, CA where the S-II second stages of the Saturn V rockets had been built.[2] The final Block I launch was conducted on October 9, 1985.
The last Block I satellite was taken out of service on November 18, 1995.
Block II satellites
Initial Block II series

Artist's impression of a Navstar-2 satellite in orbit.
The first of the nine satellites in the initial Block II series was launched February 14, 1989; the last was launched October 1, 1990.[3]
The final satellite of the series to be taken out of service was decommissioned March 15, 2007.

Block IIA series
Nineteen satellites in the Block IIA series were launched, the first on November 26, 1990 and the last on November 6, 1997. As of January 17, 2009, six satellites of this series have been removed from service.
Two of the satellites in this series, numbers 35 and 36, are equipped with laser retro-reflectors,[4] allowing them to be tracked independently of their radio signals, providing unambiguous separation of clock and ephemeris errors.

Block IIR series

Artist's impression of a GPS-IIR satellite in orbit.
The Block IIR series are "replenishment" satellites developed by Lockheed Martin. Each satellite weighs 4,480 pounds (2,030 kg) at launch and 2,370 pounds (1,080 kg) once on orbit.[5] The first attempted launch of a Block IIR satellite failed on January 17, 1997 when the Delta II rocket exploded 12 seconds into flight. The first successful launch was on July 23, 1997. Twelve satellites in the series were successfully launched.
Block IIR-M series

Artist's impression of a GPS-IIRM satellite in orbit.
The Block IIR-M satellites include a new military signal and a more robust civil signal, known as L2C.[6] There are eight satellites in the Block IIR-M series, which were built by Lockheed Martin.[7] The first Block IIR-M satellite was launched on September 26, 2005. The final launch of a IIR-M was on August 17, 2009.[1]
Block IIF series
Main article: GPS Block IIF

Artist's impression of a Navstar-2F satellite in orbit.
The Block IIF series are "follow-on" satellites developed by Boeing. On September 9, 2007 Boeing announced that it had completed assembly of the first satellite in the Block IIF series.[8] Boeing is under contract to build a total of twelve Block IIF satellites. The first was launched in May 2010 on a Delta IV rocket.[9] The second satellite was launched on July 16th 2011. The spacecraft have a mass of 1,630 kilograms (3,600 lb) and a design life of 12 years.

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