NamesNavstar 2A-18
Mission typeNavigation
OperatorU.S. Air Force
COSPAR ID1996-056A [1]
SATCAT no.24320
Mission duration7.5 years (planned)
14.75 years (achieved)
Spacecraft properties
SpacecraftGPS IIA
Spacecraft typeGPS Block IIA[2]
ManufacturerRockwell International
Launch mass840 kg (1,850 lb)
Dimensions5.3 m (17 ft) of long
Power710 watts
Start of mission
Launch date12 September 1996,
08:49:00 UTC
RocketDelta II 7925-9.5
(Delta D238)
Launch siteCape Canaveral, LC-17A
ContractorMcDonnell Douglas
Entered service17 October 1996
End of mission
DisposalGraveyard orbit
Deactivated20 July 2011
Orbital parameters
Reference systemGeocentric orbit[3]
RegimeMedium Earth orbit
SlotB2 (slot 2 plane B)
Perigee altitude20,058 km (12,463 mi)
Apogee altitude20,305 km (12,617 mi)
Period717.94 minutes
← USA-126 (GPS IIA-17)

USA-128, also known as GPS IIA-18, GPS II-27 and GPS SVN-30, is an American navigation satellite which forms part of the Global Positioning System. It was the eighteenth of nineteen Block IIA GPS satellites to be launched.


Global Positioning System (GPS) was developed by the U.S. Department of Defense to provide all-weather round-the-clock navigation capabilities for military ground, sea, and air forces. Since its implementation, GPS has also become an integral asset in numerous civilian applications and industries around the globe, including recreational used (e.g., boating, aircraft, hiking), corporate vehicle fleet tracking, and surveying. GPS employs 24 spacecraft in 20,200 km circular orbits inclined at 55.0°. These vehicles are placed in 6 orbit planes with four operational satellites in each plane.[1]

GPS Block 2 was the operational system, following the demonstration system composed of Block 1 (Navstar 1 - 11) spacecraft. These spacecraft were 3-axis stabilized, nadir pointing using reaction wheels. Dual solar arrays supplied 710 watts of power. They used S-band (SGLS) communications for control and telemetry and Ultra high frequency (UHF) cross-link between spacecraft. The payload consisted of two L-band navigation signals at 1575.42 MHz (L1) and 1227.60 MHz (L2). Each spacecraft carried 2 rubidium and 2 Cesium clocks and nuclear detonation detection sensors. Built by Rockwell Space Systems for the U.S. Air force, the spacecraft measured 5.3 m across with solar panels deployed and had a design life of 7.5 years.[1]


USA-128 was launched at 08:49:00 UTC on 12 September 1996, atop a Delta II launch vehicle, flight number D238, flying in the 7925-9.5 configuration.[4] The launch took place from Launch Complex 17A (LC-17A) at the Cape Canaveral Air Force Station (CCAFS),[5] and placed USA-128 into a transfer orbit. The satellite raised itself into medium Earth orbit using a Star-37XFP apogee motor.[2]


On 17 October 1996, USA-128 was in an orbit with a perigee of 20,058 km (12,463 mi), an apogee of 20,305 km (12,617 mi), a period of 717.94 minutes, and 54.7° of inclination to the equator.[3] It broadcasts the PRN 30 signal, and operates in slot 2 of plane B of the GPS constellation.[6] The satellite has a mass of 840 kg (1,850 lb). It had a design life of 7.5 years,[2] and was decommissioned on 20 July 2011.[7]


  1. ^ a b c "Display: Navstar 2A-18 1996-056A". NASA. 14 May 2020. Retrieved 21 December 2020. Public Domain This article incorporates text from this source, which is in the public domain.
  2. ^ a b c Krebs, Gunter. "GPS-2A (Navstar-2A)". Gunter's Space Page. Retrieved 10 July 2012.
  3. ^ a b McDowell, Jonathan. "Satellite Catalog". Jonathan's Space Report. Retrieved 11 July 2012.
  4. ^ McDowell, Jonathan. "Launch Log". Jonathan's Space Report. Retrieved 11 July 2012.
  5. ^ McDowell, Jonathan. "Launch List". Launch Vehicle Database. Jonathan's Space Report. Retrieved 11 July 2012.
  6. ^ Wade, Mark. "Navstar". Encyclopedia Astronautica. Archived from the original on 11 November 2002. Retrieved 10 July 2012.
  7. ^ "NANU 2011-048". Celestrak. Retrieved 5 September 2012.