GPS satellite blocks

[1] The GPS satellite constellation is now operated by the 2nd Navigation Warfare Squadron (2 NWS) of Mission Delta 31, United States Space Force.

The GPS satellites circle the Earth at an altitude of about 20,000 km (12,427 miles) and complete two full orbits every day.

[3] The Block I satellites were launched from Vandenberg Air Force Base using Atlas rockets that were converted intercontinental ballistic missiles.

[4] The Block I series consisted of the concept validation satellites and reflected various stages of system development.

Dual solar arrays supplied over 400 watts of power, charging nickel–cadmium batteries for operations in Earth's shadow.

The prime contractor was Rockwell International, which built a SVN 12 qualification vehicle after an amendment to the Block I contract.

Each spacecraft carried two rubidium and two cesium clocks, as well as nuclear detonation detection sensors, leading to a mass of 1,660 kg (3,660 lb).

[8] 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.

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.

[14] The first attempted launch of a Block IIR satellite failed on 17 January 1997 when the Delta II rocket exploded 12 seconds into flight.

[22] On 23 December 2018, the first GPS III satellite was launched aboard a SpaceX Falcon 9 Full Thrust.