Graham Warwick/WASHINGTON DC
Anew US Air Force acquisition strategy for global positioning system (GPS) navigation satellites will accelerate the deployment of improved anti-jamming for military use and increased integrity for civil use.
As a result, the USAF will cut back Boeing's contract to produce GPSIIF follow-on satellites and instead launch a competition to develop and build enhanced "Block III" spacecraft.
The acquisition revamp is a result of the unexpected longevity of current Boeing-built GPS II/IIA spacecraft, which has pushed back the opportunity to field sought-after improvements in the system's military and civil capability.
So far, two of 20 Lockheed Martin-built IIR replenishment satellites have been orbited. The first IIF launch has been pushed back to 2005. The USAF had 33 IIFs on order and option for delivery by 2012, but may cut this to 12.
Under the new strategy, up to 12 of the 18 IIRs remaining to be launched will be retrofitted with a second civil frequency (L2) and a new, more secure military code (M-code). The six IIFs on order, which already have the L2 signal, will be modified with a third civil signal (L5) and M-code.
The USAF expects to buy six more modified IIFs before switching procurement to the still-undefined GPSIII. Boeing's director of navigation satellite systems, Steve O'Neill, says the exact number of IIFs bought will depend on the life of the current II/IIA/IIRs.
O'Neill expects the USAF to launch three modified IIFs a year from 2005-8 and begin fielding the new GPS IIIs in 2009. The USAF says it does not have an approved schedule, but expects "competitive work will begin this year".
The USAF originally planned to begin GPS modernisation with the seventh IIF, in 2007. This was to have been the first "IIF Heavy", providing increased signal power - to overcome jamming - by using steerable spot beams.
"As satellite lifetimes increased-it became more important to field some of the new signals rather than just the high power," the USAF says. At the same time, the Kosovo conflict indicated "more intrinsic improvements to GPS were necessary", it says.
Source: Flight International
