WASHINGTON — As the U.S. Air Force prepares to launch the second GPS 2F spacecraft July 14, it continues to experiment with different modes of operation for a more robust navigation signal that is expected to be available to military users starting in 2016, a service official said July 5.
Launch of the second GPS 2F craft comes some 14 months after the first satellite in the series was carried to orbit. The current constellation of 31 active GPS satellites, which includes older GPS 2 and GPS 2R craft, is as healthy as it has ever been, government and industry officials said during a media briefing.
GPS 2F prime contractor Boeing Space and Intelligence Systems of Seal Beach, Calif., is under contract to deliver a dozen satellites, which will produce more precise position, navigation and timing signals than any previous-generation GPS craft. The satellites feature a third civilian signal known as L5 that will be used for civil and commercial aviation and search-and-rescue operations, and the military M-code signal that is expected to be more resistant to jamming attempts.
The first GPS 2F satellite, launched in May 2010, initially was broadcasting the experimental M-code signal, but the Air Force has since turned it off while engineers seek to understand the best way to operate the signal, said Col. Christopher Warack, space systems program manager at the Air Force Space and Missile Systems Center.
“What we saw with the 2F fleet was a question on the amount of margin in the power level of that signal, and we want to work at that and make sure that we’re keeping the satellite healthy,” Warack said. “There’s actually no question of whether the satellite can meet its requirements. We’re just trying to be careful and operate the satellites in the best way possible to keep them safe and … provide all the services to the users that they need.”
While GPS 2F-2 will be the 10th satellite on orbit capable of broadcasting the M-code — eight GPS 2RM satellites can also broadcast the M-code — that particular signal will not be available for operational use until 2016. GPS receivers that can acquire and utilize the M-code signal are still in the development phase, and the current GPS ground control system is not equipped for the signal, Warack said.
The next-generation GPS OCX ground system is now being developed by Raytheon Intelligence and Information Systems of Garland, Texas, and its second increment, planned for deployment in 2016, will support M-code, he said. The M-code signal also cannot be fully operational until it can be broadcast from 18 satellites on orbit.
The GPS 2F satellites are the first U.S. navigation craft to be launched on the military’s workhorse rockets, the Atlas 5 and Delta 4. GPS 2F-2 is encapsulated atop a Delta 4 rocket at Cape Canaveral Air Force Station, Fla. The rocket, built by United Launch Alliance of Denver, is powered by an RS-68 liquid-fueled engine built by Pratt & Whitney Rocketdyne of Canoga Park, Calif., and features a four-meter fairing and two strap-on solid-rocket motors built by Alliant TechSystems of Minneapolis.
After the rocket’s main booster core is jettisoned, the RL-10B2 upper-stage engine will perform a series of three burns to place the satellite into a circular orbit 17,600 kilometers above Earth, said Jim Sponnick, United Launch Alliance’s vice president of mission operations.
The Air Force will launch the remaining GPS 2F satellites on an as-needed basis, Warack said. The third craft is manifested for September 2012, but launch dates for the remaining nine have not yet been decided, he said.
Lockheed Martin Space Systems of Denver is developing the next-generation GPS 3 satellites, the first of which is planned to be ready for launch in 2014. As the Air Force stretches out the launch schedule for the remaining GPS 2F craft, it appears likely that launch of the GPS 3 satellites will also be pushed to the right, a government source said. The Air Force in its 2012 budget request disclosed plans to slow the production rate for GPS 3 satellites from three to two per year.
