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The Cape, Chapter 3, Section 4

Medium and Light Military Space Operations

NAVSTAR II Global Positioning System Missions

Following the first NAVSTAR II GPS mission on 14 February 1989, 16 highly successful NAVSTAR II missions were launched from Complex 17 between 10 June 1989 and the end of 1992. The first eight of those missions involved Model 6925 launch vehicles, and the remaining eight flights featured Model 7925s equipped with GEMs. Though all those missions were ultimately successful, countdown operations did not always lead to launches. The NAVSTAR II-2 mission lifted off Pad 17A at 2230:01Z on 10 June 1989, but only after five earlier countdowns were attempted and scrubbed in May and June 1989. The NAVSTAR II-3 mission was scheduled for launch on 11 August 1989, but it was delayed 24 hours after Pad 17A suffered a lightning strike. The NAVSTAR II-3's first launch attempt on August 12th was scrubbed due to a weather constraint violation at launch time, and a second countdown was required before the vehicle lifted off Pad 17A at 0557:59Z on 18 August 1989. The NAVSTAR II-4 mission was launched from Pad 17A on its first launch attempt at 0931:01Z on 21 October 1989, but the NAVSTAR II-5 mission was scrubbed on 10 December 1989 due to a helium problem in the vehicle's second stage. The NAVSTAR II-5 mission lifted off Pad 17A at 1810:01Z on 11 December 1989. The NAVSTAR II-6 mission lifted off Pad 17A on its first launch attempt at 2255:01Z on 24 January 1990, but the first countdown for the NAVSTAR II-7 mission was scrubbed on 21 March 1990 due to unacceptable upper level wind conditions. The mission was rescheduled, and NAVSTAR II-7 was launched successfully from Pad 17A at 0245:01Z on 26 March 1990. The NAVSTAR II-8 payload was launched after an uneventful countdown at 0539:00Z on 2 August 1990, and a Model 6925 boosted the NAVSTAR II-9 mission into orbit from Pad 17A at 2156:00Z on 1 October 1990.29

Figure 111: DELTA II Payload Encapsulation at Pad 17A
January 1989

The Model 7925 made its debut with a successful lift-off from Pad 17A at 2139:01Z on 26 November 1990. Apart from a seven-minute extension to evaluate wind data, the countdown was largely uneventful. The vehicle placed its NAVSTAR II-10 payload into the prescribed orbit. The NAVSTAR II-11 mission was scrubbed on 3 July 1991 due to the loss of a satellite communication link with the range tracking station on Ascension Island. The countdown was picked up again, and the GEM-equipped DELTA II boosted its NAVSTAR II-11 payload and the LOSAT-X payload off Pad 17A at 0232:00Z on 4 July 1991. Both payloads were released successfully. The first launch attempt for the NAVSTAR II-12 mission was aborted at 2322:00Z on 18 February 1992 due to heavy cloud cover, and the second countdown was scrubbed at 2310:00Z on February 19th for weather problems. The third and final attempt for that mission was overshadowed by bad weather and punctuated with a brief computer synchronization problem, but the final countdown on February 23rd was otherwise uneventful. The weather improved, and the DELTA II lifted off Pad 17B successfully at 2229:00Z on 23 February 1992.30

Figure 112: DELTA II Model 7925 launch
26 November 1990

The next NAVSTAR II mission also required three separate countdowns before its DELTA II Model 7925 vehicle lifted off Pad 17B on 10 April 1992. The NAVSTAR II-14 mission was launched from Pad 17B on the first launch attempt at 0920:01Z on 7 July 1992. Similarly, the NAVSTAR II-15 mission was launched from Pad 17A on its first launch attempt at 0857:00Z on 9 September 1992. The NAVSTAR II-16 countdown on November 7th was scrubbed at 0105Z due to a vehicle misfire, and the mission's next countdown on November 20th was scrubbed at 0005Z due to weather constraints. In contrast to the first two attempts, the countdown for the NAVSTAR II-16 launch on November 22nd went smoothly. There were no unscheduled holds, and the vehicle lifted off without incident at 2354:00Z on 22 November 1992. The final NAVSTAR II mission of 1992 was scrubbed on December 16th due to a vehicle anomaly which occurred during the final liquid oxygen filling procedure. The second countdown on December 18th was successful, and the DELTA II lifted the NAVSTAR II-17 payload off Pad 17B at 2216:00Z on that date. The flight was the seventeenth in a unbroken series of successful missions for the NAVSTAR II GPS program.31

The DELTA II/NAVSTAR II launch program was one the Air Force's greatest success stories at the Cape, and it is only fitting that we should note the impact of those launches on the NAVSTAR GPS constellation in the late 1980s and early 1990s. Of the ten Block I NAVSTAR spacecraft orbited before November 1985, seven were still in operation when the first NAVSTAR II mission was launched in February 1989. In 1988, the Air Force and the Joint Requirements Oversight Committee of the Joint Chiefs of Staff supported a return to the original plan of a 24-satellite GPS constellation. On 27 February 1989, the Air Force directed Air Force Systems Command to establish and maintain a GPS constellation of 21 primary satellites, plus active orbiting spares (i.e., a 24-satellite constellation). The last two NAVSTAR II satellites were removed from the Space Shuttle's payload manifest in the spring of 1989, so the entire weight of the expanded constellation fell on the shoulders of the DELTA II launch program.32

The GPS Program Office hoped to have five NAVSTAR II satellites in orbit by the end of September 1989, but only three of those spacecraft had been launched by that time. Since twelve Block II satellites would be needed to give the GPS constellation its first worldwide two-dimensional navigation capability, planners estimated that capability could not be achieved before the spring of 1991. In point of fact, six more NAVSTAR II satellites were launched over the next year, and Iraq's invasion of Kuwait in August 1990 provided additional incentive for McDonnell Douglas and the Air Force to rise to the challenge. NAVSTAR II-9 (the last of the six NAVSTARs mentioned) lifted off on 1 October 1990, and it was placed in orbit over the Middle East. The satellite's on-orbit testing program was completed in record time, and NAVSTAR II-9 was turned over to Air Force Space Command on 24 October 1990. NAVSTAR II-10 was launched successfully on 26 November 1990. With II-10 in operation, the GPS network provided two-dimensional coordinates with an average accuracy of 4.5 meters during DESERT STORM. The NAVSTAR system's three-dimensional accuracy averaged 8.3 meters during the war. The GPS Program Office hoped to launch five Block IIA NAVSTAR spacecraft by October 1991, but component problems associated with the new design caused lengthy delays. Only two Block IIA missions were launched by October 1991, but five more Block IIA launches were completed by the end of 1992. The constellation was well on its way to full operational status by the beginning of 1993.33

The Cape: Miltary Space Operations 1971-1992
by Mark C. Cleary, Chief Historian
45 Space Wing Office of History
1201 Minuteman Ave, Patrick AFB, FL 32925

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