GPS IIA in assembly - Credit: Hughes. 34,327 bytes. 310 x 400 pixels.

GPS Block 2 is the Operational system, following the Demonstration system comprised of Block 1 spacecraft. The Block 2A are "Advanced" versions of this spacecraft. The complete constellation has 24 spacecraft in 6 high-altitude orbit planes. Spacecraft: 3-Axis stabilised, nadir pointing using reaction wheels. Dual solar arrays supply 710 watts (EOL). S-Band (SGLS) communications for control and telemetry. UHF cross-link between spacecraft. Hydrazine propulsion system. Payload: Two L-Band navigation signals at 1575.42 MHz (L1) and 1227.60 MHz (L2). Each spacecraft carries 2 rubidium and 2 caesium clocks. Also carry nuclear detonation detection sensors.
Financial/Operational:
Launches scheduled for Proton, Atlas, and Delta. Satellite costs: Block I $ 20 million each, Block II $ 50 million, Block IIA $ 40 million.

Design Life: 7.5 years. Total Mass: 1,665 kg.

Second generation Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spent boosters, spent maneuvering stages, shrouds and other non-functional objects (US Cat D).

Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).

Global Positioning System. Spent boosters, spent maneuvering stages, shrouds and other non-functional objects (US Cat D).

Global Positioning System. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).

Global Positioning System. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).

Global Positioning System. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).

Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).

Global Positioning System. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).

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GPS Block 2R Credit: USAF. 11,556 bytes. 270 x 211 pixels.

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Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning SYstem. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Global Positioning System. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

Final element of initial GPS constellation. Spacecraft engaged in practical applications and uses of space technology such as weather or communication (US Cat C).

MEO.

Third GPS Block 2R satellite. SVN 46 replaced SVN 50 which had been damaged by rain on Pad 17 earlier while being prepared for launch earlier in the year.

Navstar Block IIR GPS navigation satellite, GPS IIR-4 or SVN 51. Placed into an elliptical transfer orbit. The satellite's Thiokol Star 37 apogee motor was used to circularise the orbit at 20,000 km.

• 4 - McDowell, Jonathan, Jonathan's Space Report (Internet Newsletter), Harvard University, Weekly, 1989 to Present. HTML when accessed: ftp://sao-ftp.harvard.edu/pub/jcm/space/news
• 6 - JPL Mission and Spacecraft Library, Jet Propulsion Laboratory, 1997. HTML when accessed: http://msl.jpl.nasa.gov/home.html