GPS satellite blocks

Rockwell International was awarded a contract in 1974 to build the first eight Block I satellites. In 1978, the contract was extended to build an additional three Block I satellites. 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 18 December 1981. 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, California where the S-II second stages of the Saturn V rockets were built. The Block I series consisted of the concept validation satellites and reflected various stages of system development. Lessons learned from the 10 satellites in the series were incorporated into the fully operational Block II series. Dual solar arrays supplied over 400 watts of power, charging nickel–cadmium batteries for operations in Earth's shadow. S-band communications were used for control and telemetry, while an UHF channel provided cross-links between spacecraft. A hydrazine propulsion system was used for orbital correction. The payload included two L-band navigation signals at 1575.42 MHz (L1) and 1227.60 MHz (L2). The final Block I launch was conducted on 9 October 1985, but the last Block I satellite was not taken out of service until 18 November 1995, well past its 5-year design life. == Block II satellites ==

The Block II satellites were the first full scale operational GPS satellites, designed to provide 14 days of operation without any contact from the control segment. The prime contractor was Rockwell International, which built a SVN 12 qualification vehicle after an amendment to the Block I contract. In 1983, the company was awarded an additional contract to build 28 Block II/IIA satellites. Block II spacecraft were three-axis stabilized, with ground pointing using reaction wheels. Two solar arrays supplied 710 watts of power, while S-band communications were used for control and telemetry. A UHF channel was used for cross-links between spacecraft. A hydrazine propulsion system was used for orbital correction. The payload included two L-band GPS signals at 1575.42 MHz (L1) and 1227.60 MHz (L2). Each spacecraft carried two rubidium and two cesium clocks, as well as nuclear detonation detection sensors, leading to a mass of . The first of the nine satellites in the initial Block II series was launched on 14 February 1989; the last was launched on 1 October 1990. The final satellite of the series to be taken out of service was decommissioned on 15 March 2007, well past its 7.5 year design life. Block IIA series The Block IIA satellites were slightly improved versions of the Block II series, designed to provide 180 days of operation without contact from the control segment. However, the mass increased to , with no increase to the 7.5 year design life. Nineteen satellites in the Block IIA series were launched, the first on 26 November 1990 and the last on 6 November 1997. Two of the satellites in this series, numbers 35 and 36, were equipped with laser retro-reflectors, allowing them to be tracked independently of their radio signals, providing unambiguous separation of clock and ephemeris errors. SVN-34, the last Block IIA satellite, broadcast on the PRN 18 signal. It was removed from service on 9 October 2019 but kept as an on-orbit spare until April 2020. Block IIR series The Block IIR series are "replenishment" (replacement) satellites developed by Lockheed Martin. Each satellite weighs at launch and once on orbit. There are eight satellites in the Block IIR-M series, which were built by Lockheed Martin. The first Block IIR-M satellite was launched on 26 September 2005. The final launch of a IIR-M was on 17 August 2009. They also had the same 7.5 year design life as their predecessors. Block IIF series The Block IIF series are "follow-on" satellites developed by Boeing and first designed with the operational L5 signal in mind. The satellite has a mass of and an increased design life of 12 years. The first Block IIF space vehicle was launched in May 2010 on a Delta IV rocket. The twelfth and final IIF launch was on 5 February 2016. == Block III satellites ==

Block III series GPS Block III is the first series of third-generation GPS satellites, incorporating new signals (such as L1C) and broadcasting at higher power levels. Their improved 15 year design life is 3x that of the first series. On 23 December 2018, the first GPS III satellite was launched aboard a SpaceX Falcon 9 Full Thrust. The last GPS III satellite is SV10, launched in April 2026. Block IIIF series The Block IIIF series is the second set of GPS Block III satellites, which will consist of up to 22 space vehicles. Block IIIF launches are expected to begin no earlier than 2027 and continue through 2037. File:GPS-IIR.jpg|Artist's impression of a GPS-IIR satellite in orbit File:GPS-IIRM.jpg|Artist's impression of a GPS-IIRM satellite in orbit File:Navstar-2F.jpg|Artist's impression of a Navstar-2F satellite in orbit File:GPS Block IIIA.jpg|Artist's impression of a GPS Block III satellite in orbit == See also ==