GPS 2F-7 Launch Caps Air Force Use of C-band Tracking Radar

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WASHINGTON — The successful launch Aug. 1 of the U.S. Air Force’s seventh GPS 2F navigation satellite from Cape Canaveral Air Force Station, Florida, marked the final time the service is expected to rely on C-band radars to track rockets immediately following liftoff.

Future Air Force launches, both from the Cape and from Vandenberg Air Force Base in California, will rely on GPS signals for post-liftoff tracking, service officials said. The Air Force and its primary launch services provider, United Launch Alliance of Denver, have been working for years on the capability, which features rocket-mounted GPS receivers that transmit position-location data to controllers on the ground.

“It’s something that’s been a long time coming,” Walt Lauderdale, GPS 2F-7 mission director, said during a July 25 conference call with reporters. The new technique has been tested and proven at both at Cape Canaveral and Vandenberg over the last few years, he said.

C-band radars have been tracking U.S. rocket flights since the dawn of the Space Age. But their accuracy can be thrown off by changes in a rocket’s flight angle, and they also are expensive to maintain, Air Force officials have said.

In addition, there have been reliability issues, a recent example being an electrical short that crippled a radar at Cape Canaveral in March, delaying the launch of a classified satellite for the U.S. National Reconnaissance Office. The delay trickled down to other launches, postponing a Space Exploration Technologies Corp. cargo resupply mission to the international space station.

The first launch relying exclusively on GPS metric tracking will be that of DigitalGlobe’s WorldView-3 imaging satellite, now slated to take place Aug. 13 from Vandenberg aboard a ULA-built Atlas 5 rocket provided by Lockheed Martin Commercial Launch Services. The launch will be a rare commercial mission for the Atlas 5, which is used primarily for U.S. government satellites.

The GPS 2F-7 satellite also was launched by an Atlas 5, which is powered by Russian-built RD-180 main engine whose future has come into question amid a downturn in U.S. Russian relations. There are now 14 RD-180s left in the United States, although ULA said it expects to take delivery of additional engines in August.

The launch was ULA’s second successful mission in four days, a record turnaround time for the company. The previous mission, aboard a Delta 4 rocket, placed three space surveillance satellites into orbit.

The GPS 2F satellites, built by Boeing Space and Intelligence Systems of El Segundo, California, provide better accuracy and resistance to jamming than the previous-generation GPS satellites, most of which are still in operation. The launch helps bolster a GPS fleet whose satellites are beginning to show their age, Air Force officials say.

The new satellite will be one of 31 active satellites in the constellation. Once GPS 2F-7 checks out on orbit, the Air Force plans to move one of its older GPS 2A satellites into a reserve mode, said Col. Bill Cooley, head of the GPS directorate at Air Force Space and Missile Systems Center in Los Angeles.

The GPS 2A satellites had a life expectancy of 7.5 years. The satellite to be placed in reserve mode is 22 years old, Cooley said.

Cooley described the launch as part of “the most aggressive launch campaign schedule” for the GPS program since 1993.

“Our robust launch tempo requires vigilance and attention to detail, and mission success is our top priority,” Craig Cooning, president of Boeing Network & Space Systems, said in an Aug. 2 press release. “We continue to partner with the Air Force and ULA to effectively execute the launch schedule.”

The Air Force has taken a series of steps in recent years to extend the life of the on-orbit GPS satellites, including changing the way it charges the batteries on some satellites.

The Air Force expects to launch one more GPS 2F satellite in October, three in 2015 and the last in 2016. The next-generation GPS 3 satellites are slated to start launching in 2016.