Delta rocket launch to fill vacant hole in GPS network
BY JUSTIN RAY
Posted: April 19, 2000
A Boeing Delta 2 rocket is slated for liftoff at 11:05 p.m. EDT (0305 GMT Saturday) from pad 17A at Cape Canaveral Air Force Station in Florida. A 30-minute launch window will extend to 11:35 p.m. EDT.
Follow the countdown and launch in our Mission Status Center.
Air Force officials quickly changed the seemingly routine launch of another NAVSTAR GPS satellite into a full-fledged replacement mission after the GPS 2-1 craft reached the end of its life on March 26. It was decommissioned on April 14, well exceeding its seven-year design life.
The veteran satellite served as the cornerstone of the Air Force's highly successful GPS constellation of 24 spacecraft that circle 10,900 miles above Earth, providing precision location, speed and timing information to guide U.S. military troops, aircraft, submarines, ships, weapons and civilians around the world.
Lofted on February 14, 1989, GPS 2-1 was built by Rockwell International. Since then, two advanced generations of GPS satellites have been developed and flown. Known as Blocks 2A and 2R, these satellite models have allowed the military to enhance the capabilities of GPS.
Sitting atop the $50 million Delta 2 for this week's launch is the fourth GPS Block 2R satellite manufactured by Lockheed Martin Space Systems, valued at $42 million. Block 2R craft, the latest generation, were built with improvements over early satellites including the ability to operate longer when out of contact with ground controllers, better accuracy by communicating with other GPS satellites, larger fuel supplies and additional radiation protection.
Officials were originally aiming the new satellite for another part of the GPS constellation. But when the GPS 2-1 spacecraft showed signs it was about to stop working, the launch was replanned.
For those of you keeping score, GPS 2-1 is officially known in Air Force jargon as Space Vehicle No. 14 and the new GPS 2R-4 is SV No. 51.
The loss of one satellite, however, has not threatened the GPS network, said Capt. Gerald Anderson, chief of launch operations for the Air Force's GPS program.
"Right now the constellation is healthy," he said in an interview this week.
Friday's launch will insert the GPS 2R-4 satellite into the so-called E1 slot of the constellation, previously occupied by GPS 2-1.
"This launch will directly replace a satellite that has reached the end of its life," Anderson said.
After the new satellite arrives in space, it will be maneuvered into the GPS network and tested. The Air Force expects the craft to enter service on May 15, said Maj. David Keller, chief of aquisition operations for the GPS Joint Program Office.
Users of GPS rely on handheld receivers that pick up signals from four satellites passing overhead at any given time. The receiver measures the time delay for the signal to reach itself from the satellite, which ultimately shows the distance to the orbiting satellite.
Military users can then determine their exact location to within feet, speed within a fraction of a mile per hour and time to within a millionth of a second whether it be on the ground, in the air or at sea. GPS was used extensively in the featureless desert battlefield of the Gulf War.
Civilian receivers have less accuracy but are popular nonetheless for a wide-range of users like hikers, boaters, pilots and mapmakers.
Preparations on track for liftoff
The satellite was transported to the launch pad last week and the protective nose cone of the rocket was installed over the weekend.
Like the previous 31 GPS launches, Boeing will use its three-stage Delta 2 rocket featuring nine strap-on solid rocket motors and a 9.5-foot diameter payload fairing.
The early weather forecast is calling for favorable conditions Friday evening with an 80 percent chance of acceptable conditions. The main threat will come in the form of thunderstorm anvil clouds that might develop near a weather front expected to approach the Cape late Friday.
At liftoff time, Air Force Launch Weather Officer Joel Tumbiolo predicts a few clouds at 3,000 feet and scattered clouds at 25,000 feet, visibility of 10 miles or better, west-southwesterly winds 12 gusting to 20 knots, a temperature of 74 to 76 degrees F and relative humidity of 50 percent.
If the launch is delayed until Saturday night for some reason, there is a 90 percent chance of acceptable conditions with the only concern being gusty ground winds.
This will be Boeing's third Delta 2 rocket launch of 2000 and the second to occur from the Cape.
Animation depicts a GPS satellite and the Global Positioning System orbital constellation.
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Flight Data File
Vehicle: Delta 2 (7925)
Payload: GPS 2R-4
Launch date: April 22, 2000
Launch window: 0305-0335 GMT (11:05-11:35 p.m. EDT on 21st)
Launch site: SLC-17A, Cape Canaveral, Fla.
Launch timeline - Chart with times and descriptions of events to occur during the launch.
Orbit trace - A map shows the launch track for the mission.
Delta 2 rocket - Overview of the Delta 2 7925-model rocket used to launch GPS satellites.
Global Positioning System - Description of the U.S. Air Force's space-based navigation network.
GPS constellation - Chart shows the current status of the orbiting GPS satellite fleet.
Explore the Net
Delta 2 - Official Web site of Boeing's Delta 2 expendable launch vehicle program.
GPS - Global Positioning System Joint Program Office at U.S. Air Force.
LMMS - Lockheed Martin Missiles & Space built GPS 2R-4.
1st Space Launch Squadron - Oversees Delta rocket launches and facilities at Cape Canaveral Air Force Station in Florida.
History of Delta - A private Web site devoted to past Delta launches with valuable facts and figures.
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