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Navstar 7

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Navstar 7
NamesGPS I-7
GPS SVN-7
Mission typeNavigation
Technology
OperatorU.S. Air Force
Mission duration5 years (planned)
Launch failure
Spacecraft properties
SpacecraftNavstar
Spacecraft typeGPS Block I
ManufacturerRockwell Space Systems[1]
Launch mass758 kg (1,671 lb)[1]
Dimensions5.3 meters of long
Power400 watts
Start of mission
Launch date19 December 1981, 01:10:00UTC
RocketAtlas E/ SGS-1
(Atlas-76E)[2]
Launch siteVandenberg,SLC-3E
ContractorConvair
General Dynamics
Entered serviceLaunch failure
Orbital parameters
Reference systemGeocentric orbit(planned)
RegimeMedium Earth orbit
(Semi-synchronous)
Altitude20,200 km
Inclination63.0°
Period720 minutes
OPS 5118(Navstar 6)
OPS 9794(Navstar 8) →

Navstar 7,also known asGPS I-7andGPS SVN-7,was an Americannavigation satellitewhich was lost in a launch failure in 1981. It was intended to be used in theGlobal Positioning Systemdevelopment program. It was the seventh of elevenBlock IGPS satellites to be launched, and the only one to fail to achieve orbit.[1]

Background

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Global Positioning System (GPS) was developed by theU.S. Department of Defenseto 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°. These vehicles are placed in 6 orbit planes with four operational satellites in each plane.[3]

Spacecraft

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The first eleven spacecraft (GPS Block 1) were used to demonstrate the feasibility of the GPS system. They were 3-axis stabilized, nadir pointing usingreaction wheels.Dual solar arrays supplied over 400 watts. They hadS-bandcommunications for control andtelemetryandUltra high frequency(UHF) cross-link between spacecraft. They were manufactured byRockwell Space Systems,were 5.3 meters across withsolar panelsdeployed, and had a design life expectancy of 5 years. Unlike the later operational satellites, GPS Block 1 spacecraft were inclined at 63°.[3]

Launch

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Navstar 7 was launched at 01:10 UTC on 19 December 1981, atop anAtlas Elaunch vehiclewith an SGS-1upper stage.The Atlas used had the serial number 76E, and was originally built as an Atlas E.[2]The launch took place fromSpace Launch Complex 3EatVandenberg Air Force Base.[4]

During preparations for launch, a seal on the number B2 engine of theMA-3booster section of the Atlas was replaced. Sealant from this seeped into three coolant holes, plugging them. Four seconds after liftoff, the engine overheated and burned through its gas generator, severing an oxidiser line. Within seven and a half seconds of launch, the engine lost thrust, causing the rocket to pitch out of control.[5]It was destroyed byrange safety officer,[6]with debris landing within 150 m (490 ft) of the launch pad, less than twenty seconds after liftoff.[5]

Mission

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If the launch had been successful, it would have placed Navstar 7 into a transfer orbit, from which the satellite would have raised itself intomedium Earth orbitby means of aStar-27apogee motor.[1]The spacecraft had a design life of 5 years and a mass of 758 kg (1,671 lb).[1]

References

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  1. ^abcdeKrebs, Gunter."GPS (Navstar)".Gunter's Space Page.Retrieved12 July2012.
  2. ^abMcDowell, Jonathan."Launch Log".Jonathan's Space Report.Retrieved12 July2012.
  3. ^ab"Display: Navstar 6 1980-032A".NASA. 14 May 2020.Retrieved21 November2020.Public DomainThis article incorporates text from this source, which is in thepublic domain.
  4. ^McDowell, Jonathan."Launch List".Launch Vehicle Database.Jonathan's Space Report. Archived fromthe originalon 15 August 2020.Retrieved12 July2012.
  5. ^abEleazer, Wayne (31 January 2011)."Launch failures: the" Oops! "factor".The Space Review.Retrieved12 July2012.
  6. ^"Booster Destroyed on Liftoff".The Press-Courier.Vol. 45, no. 159. Oxnard, California. 19 December 1981. p. 3.