USAF foot-dragging delays higher-precision GPS network

Aviation International News » October 2002
May 7, 2008, 5:02 AM

Navstar, the official U.S. Air Force program moniker for the constellation of satellites most of us refer to simply as GPS, has undergone a multitude of technical changes and upgrades in the nearly 30 years since a group of military and civil engineers first sat down in the Pentagon to talk about the far-reaching precision navigation concept. Now, in the wake of numerous schedule slippages and a budget crunch related to more pressing security needs, the USAF has delayed by at least six months green lighting the next major series of improvements to GPS designed to boost satellite signals, make them harder to jam and provide new-generation GPS service to civil and military users for the next 30 years.

Sometime early next year it is anticipated that the USAF will release a request for proposals for the GPS III program, after an original schedule that called for submittal of the RFP in August. This follows several program slippages and comes on the heels of the recent completion of a study by Boeing, Lockheed Martin and Spectrum Astro to pin down the new architecture for the future GPS network.

Defense Department officials at this point are unsure how the latest six-month delay to the original program schedule will affect the actual planned launch date for the first GPS III satellites, now scheduled for initial launch in 2010 or 2011. Last month the Air Force was on the verge of submitting its revised timeline to the Pentagon.

USAF officials now face a conundrum. Not only are the current, earlier-generation GPS satellites lasting much longer in orbit than originally expected, but the Air Force is also experiencing a budget shortfall due to other space programs having higher national security priorities. Added to this, the USAF recently learned that the not-yet-built GPS III satellites could cost as much as three times the current units. The net result, according to Washington insiders, is that the first GPS III launch could slip to 2015 or later, and it might now be as long as 2025 before the completely new constellation is in place.

For the time being, the USAF is content to celebrate the five-year anniversary of the current GPS Block IIR program, the first successful launch for which came on July 23, 1997, a date that heralded a new era in GPS operational performance, specifically better navigational accuracy.

The USAF plans to launch 14 new GPS IIR satellites over the next four years, and then gear up for the first research-and-development satellites for GPS III.
Meanwhile, Boeing and Lockheed Martin continue to perform engineering upgrades to GPS IIR-M and IIF satellites, which will feature higher-power signals, making them more difficult to jam. The first of these satellites, considered a stopgap measure until GPS III emerges, are scheduled for launch late next year.

Boeing Space and Communications earlier this year received approval from the USAF to move forward with space vehicle production for the GPS IIF modernization program. GPS IIF is the next step in enhancing the satellite constellation’s capabilities to support the national infrastructure for homeland security and national defense, and at the same time will improve system capabilities for all GPS users, said Mike Rizzo, director of navigation systems for Boeing Space and Communications in Seal Beach, Calif.

The added capabilities include a new signal for civilian users and secure operational M-codes for the military. The new civilian signal, designed to operate in the protected aeronautical radio navigation system frequency band, will provide redundant “safety-of-life services” for civil aviation users and increased accuracy for a host of other users worldwide. In addition, Boeing said GPS IIF satellites themselves are compatible with the Air Force’s evolved expendable launch vehicle (EELV) and will provide 20 percent more in-orbit life than previous GPS satellites.

“Designed for flexibility and growth, the GPS IIF system architecture can affordably accommodate hardware and software changes through incremental technology upgrades to improve efficiency and introduce new military capabilities, including anti-jam, greater accuracy, better availability and higher integrity,” said Rizzo. “This approach to the GPS IIF program will, in turn, reduce the technical risks inherent in developing GPS III.”

In the aftermath of September 11, the threat of deliberate GPS signal interference continues to concern government officials. A study of GPS vulnerability, prepared by the DOT’s Volpe Technical Center in Cambridge, Mass., examined the full range of GPS vulnerabilities, from natural disturbances to intentional signal disruptions, all of which could potentially cause temporary or longer-term loss of signals.

The report stated that the most critical GPS deficiencies were its extremely low-powered signals and its single civil frequency. These deficiencies, it said, would be corrected in GPS III, which will transmit at much higher power (100 times that of current-generation satellites) over two dedicated civil frequencies, thereby virtually eliminating natural interference while at the same time thwarting inexpensive, pocket-sized GPS signal jammers.

However, the report noted that GPS III is not expected to become fully operational until between 2012 and 2015. Until then, GPS remains “extremely vulnerable” to interference, the report stated. The Volpe Center therefore recommended a comprehensive analysis of GPS backup navigation and precision-timing options, including VOR/DME, ILS, loran-C, inertial navigation systems and improved operating procedures, which could be used in conjunction with LAAS to ensure the veracity of GPS signals.

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