GPS Block II
In the aftermath of the Challenger accident, the Air Force decided to remove the
Navstars from the Shuttle manifest, and to launch them on an improved version
of the proven Delta launch vehicle, known as the Delta II. A total of 20 of these
rockets were ordered. Block II SVs were built by Rockwell International.
Significant Block II SV enhancements to the
signal-in-space (SIS) interface were:
- Radiation hardened electronics to prevent random
memory upset events to improve SIS reliability
and survivability.
- Capacity to store 180 days worth of 50 Hz
navigation message data, compared to only 3.5
days worth of storage in the Block I SVs, to
guarantee SIS availability.
- Full selective availability (SA) and anti-spoof
(A-S) capabilities to provide for SIS security.
- Automatic detection of certain error conditions
and switching to non-standard PRN Code
transmission or default navigation message data
(alternating ones and zeros) to protect users
from tracking a faulty SV and maximize SIS
integrity.
With the launch of five new Navstar satellites in 1989, the
Air Force began to implement the full complement of 21 active and 3 spare
satellites will be required for the system can provide nearly continuous global
coverage.(1) The first of 28 Block II SVs, SV PRN number 14, was launched on 14 February 1989 from Cape Canaveral AFS, FL using a Delta II MLV and was set "healthy" in its broadcast 50 Hz navigation message for global use on 15 April 1989. Although the first two satellites launched had been nicknamed Elvis
(Presley) and Janis (Joplin), this practice ceased with the third and subsequent
launches.(2) Rockwell International was also the prime contractor for Block IIA.
The design life of the operational satellites is seven and one-half years.(3)
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Navstar GPS Specifications
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Weight:
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1,860 pounds (in orbit)
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Orbit altitude:
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10,900 miles
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Power plant:
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Solar panels generating 700 watts
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Dimension:
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5 feet wide, 17.5 feet long (length includes wingspan)
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Primary contractor:
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Rockwell International - Block I, IIA
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References
1. Kolcum, Edward, "First USAF/McDonnell Douglas Delta 2 Launch Begins New Military
Space Era," Aviation Week & Space Technology, 20 February 1989, page 18-19.
2. "News and Comment," Air Force Magazine, October 1989, page 29.
3. Maj Michael J. Muolo, Maj Richard A. Hand, Maj Bonnie Houchen and Maj Lou Larson,
Space Handbook A War Fighter's Guide to Space -- Volume One, AU-18, Air University Air
Command and Staff College, (Air University Press, Maxwell Air Force Base, Alabama,
December 1993).
http://www.fas.org/spp/military/program/nav/gps_2.htm
Implemented by Charles P. Vick, Sara D. Berman, and
Christina Lindborg, 1997 Scoville Fellow
Maintained by Robert Sherman
Originally created by John Pike
Updated Sunday, April 13, 1997