The delayed release of a request for proposals for design of the next-generation global positioning system, GPS III, is planned for late January. The US Air Force is hoping for Department of Defense approval for its GPS III acquisition strategy in December and plans to award one or two programme definition and risk reduction contracts in July.
The first launch of a GPS III satellite is now scheduled for 2012, says US Air Force GPS chief engineer Col Rick Reaser, a slip from the previously projected date of 2009. Launches of the modernised Block IIR-M and Block IIF satellites have also slipped "by a few months" because the in-orbit satellites are lasting longer than expected, he says.
Lockheed Martin IIR-M satellites will be launched between 2003 and 2006 and the Boeing-built IIFs between 2005 and 2010 to replenish and modernise the GPS constellation. The slips will delay initial operational capability for both the more-robust military M-code and additional, more accurate than current civil frequencies, Reaser says.
Boeing, Lockheed Martin and Spectrum Astro are competing for GPS III, expected to involve production of 30 satellites. In addition to new military and civil signals, GPS IIIs will have more broadcast power, to overcome jamming and interference, and will provide more accurate positioning. Civil accuracy will be 0.5m (20in) horizontally and 1m vertically, says Reaser.
Despite a GPS IIR having been damaged on the launch pad, delaying the next replenishment flight until late February, the constellation is healthy, Reaser says. There are 27 satellites operational, against a minimum requirement of 21, although several have lost redundancy in one or more systems.
Reaser dismisses concerns over the constellation's status raised by the redundancy issues and delayed replenishment. "GPS is healthy. That's why we have stretched out the launches," he says. "And we are still on track to deliver improved performance."
Source: Flight International
