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Archive for August, 2009

20-Aug-09 | Delta flight 343 – NAVSTAR IIR-21 (M8)

On Monday, 17 August 2009, the last U.S. Air Force Delta II was launched from Cape Canaveral Air Force Station, placing a GPS satellite successfully into its transfer orbit.

As has become almost casually expected for a launch system that has now completed its 89th consecutive success, the terminal countdown for this flight encountered no major issues, and as dawn broke over the Florida coast, weather concerns—cumulus clouds and a chance of rain—dissipated. Liftoff occurred at the opening of the four-minute launch window, at an official range time of 06:35:00.231 EDT, with release into a nominal transfer orbit happening a little more than 68 minutes later.

NAVSTAR IIR-21 is the last of eight “modernized” replenishment spacecraft to join the GPS constellation. It will replace NAVSTAR IIA-26, an aging but still active bird that has lasted nearly twice as long as its seven-year design life since its launch in July 1996 aboard Delta 237.

Despite the success, this was a deeply melancholy event for all concerned, for this was the last time the Air Force would launch a vehicle that owed its very existence to that service. The Delta II rocket was developed by McDonnell-Douglas in response to an Air Force request for proposals following the loss of Space Shuttle Challenger in 1986, as a means to clear the resulting backlog in the launch manifest. The choice of Delta II reawakened a production line which had already been shut down, and resulted in a launch vehicle that has tallied one of the greatest records of reliability in the Space Age: over 99% in 144 launches. To date, all operational GPS satellites have been lofted on Delta II rockets: 49 in all, with only one of those failing to orbit.

Now, this chapter of spaceflight history has closed. The increased size and capability of future GPS satellites mean that they have outgrown the payload capacity of Delta II, and the Department of Defense will move to its two EELV options (Delta IV and Atlas V) for GPS as well as other missions. The launch also marked the final scheduled use of SLC-17A, one of two launch pads built at Canaveral in 1956 for the Thor ballistic missile program—a missile that formed the first stage of the original Delta model.

The military’s move away from Delta II, combined with budget concerns at NASA that prevent it from putting up enough missions to maintain the system singlehandedly, have resulted in the shutdown of the launch vehicle’s production line. A total of seven flights remain on the Delta II manifest—five from the west coast launch site at Vandenberg Air Force Base, and two from Canaveral’s SLC-17B. Another five vehicles have been built by Boeing and are in storage awaiting sale. After that, barring a major sea change in the industry, the Delta era—presently more than 49 years in the making—will come to an end.



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