Delta 4 rocket ready for mission for U.S. military
BY JUSTIN RAY
Posted: December 1, 2009
The United Launch Alliance-built vehicle will perform a 40-minute flight to supersynchronous transfer orbit for deployment of the Air Force's third Wideband Global SATCOM communications spacecraft, known as WGS 3.
WGS satellites are giving a major upgrade to the military's main communications infrastructure, replacing the aging Defense Satellite Communications System (DSCS) spacecraft. Each WGS has 10 times the capacity of a DSCS satellite, allowing users to process and receive data quicker than ever before.
"The WGS 3 satellite has gone through a very rigorous test program to ensure that the satellite has been designed and tested and will perform as intended on-orbit," said Mark Spiwak, the WGS program director for satellite-builder Boeing.
"We are very proud to be providing this awesome capability to the warfighter in partnership with the United States Air Force and are looking forward to a great launch."
WGS 1 entered service last year to cover the vast Pacific Command that spans the U.S. western coast all the way to Southeast Asia. The WGS 2 satellite launched earlier this year was placed into operation over the Indian Ocean for use by U.S. Central Command to provide coverage for the warfighters in Afghanistan, Iraq and other parts of Southwest Asia.
The new WGS 3 satellite will be positioned above the Eastern Atlantic at an orbital slot of 12 degrees West longitude for U.S. European Command and U.S. Africa Command, plus lend additional support over the Middle East.
"WGS 3 is the next step in deploying Wideband Global SATCOM to augment and eventually replace the legacy Defense Satellite Communications System, or DSCS, which has been the Department of Defense's backbone for satellite communications over the last three decades," said Col. Bill Harding, vice commander, Military Satellite Communications Systems Wing.
"WGS 3 is slated for operations over EUCOM and AFRICOM and will provide an order of magnitude increase in military communications bandwidth for Soldiers, Sailors, Airmen and Marines."
Following this week's launch, it will be maneuvered into a circular geostationary orbit 22,300 miles above the planet where it can match the Earth's rotation and appear parked over one area of the globe. On-orbit testing is scheduled to last a few months, enabling the craft to begin full use next April.
The WGS spacecraft are constructed around Boeing's powerhouse 702-model design used by commercial satellite operators. But within the WGS craft are Ka- and X-band military communications packages to serve forces stationed around the globe.
The WGS craft offer X-band communications, like the venerable DSCS satellites, to relay data, photos and video to troops on the battlefield.
What's new on WGS is Ka-band communications. Officials describe the extra frequency as a way of serving up large amounts of information for reception by U.S. and allied forces across a wide area.
The first two WGS satellites were hauled into space aboard Atlas 5 rockets. But WGS 3 will ride atop the Delta 4, the other rocket in the Air Force's Evolved Expendable Launch Vehicle fleet.
The WGS 3 spacecraft, weighing about 6.5 tons, will need a hefty version of the Delta 4 to reach its targeted orbit. That rocket configuration is known as the Medium+ (5,4).
Not yet flown before, this version of the Delta is distinguished by a five-meter payload shroud and four solid rocket boosters. Previous Medium+ rockets have flown with the smaller four-meter nose cone and only two solid motors.
"The fact that this is the first 5,4 configuration means that there are several 'new parts' of the vehicle," the Air Force's Launch and Range Systems Wing says.
"The five-meter, 47-foot-long composite payload fairing is a first flight item, as well as the four solid rocket motor configuration, two of which are thrust vector controlled, and two are fixed nozzle. For added support, we also use the X-brace within the Common Booster Core."
The cryogenic main engine and all four solids will be ignited on the launch pad, rapidly accelerating the 217-foot-tall rocket into the nighttime sky. The strap-on motors fire for 94 seconds, then burn out and separate from the first stage about 22 nautical miles up.
The RS-68 engine continues its firing through the initial four minutes of flight by consuming liquid hydrogen and liquid oxygen. Shortly before the first stage's burn concludes, having already climbed beyond the edge of space, the nose shroud covering the satellite will be jettisoned at an altitude of 68 nautical miles.
After the first stage separates 100 nautical miles over the ocean, the upper stage's cryogenic RL10B-2 powerplant will ignite for a 16-minute firing that propels the vehicle into an elliptical parking orbit of 100 by 3,714 nautical miles and inclined 25.59 degrees to the equator.
The rocket will coast in that temporary orbit only briefly as it nears the western coast of Africa. The engine is restarted to burn for three more minutes that sends WGS 3 toward its egg-shaped transfer orbit looping from 237 nautical miles at its closest point with Earth to 36,167 nautical miles at the farthest point and inclined 24 degrees.
The payload separates from the launcher 40 minutes and 32 seconds after liftoff while soaring away from the planet over the Indian Ocean.
This launch will mark the 11th for the Delta 4 family of rockets since 2002.
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