Operators of the Global Positioning System have brought a decommissioned satellite back to life to replace an ailing craft in the precision navigation network, the Air Force said.

An artist's concept of GPS 2A satellite. Credit: Air Force/Boeing

The GPS 2A-22 spacecraft had been removed from active duty two years ago to accommodate the deployment of a fresh bird into the constellation. Now, the Boeing-built satellite is back in action to transmit the timing and location signals to users around the world.

Launched in August 1993 atop a Delta 2 rocket from Cape Canaveral, the satellite has long surpassed its 7-year design life. But with some use still left to give, the 2nd Space Operations Squadron at Schreiver Air Force Base in Colorado have taken the rare step of reactivating it.

"My hat goes off to our operators, analysts, and contractor support personnel -- their superior care and feeding of our constellation is the reason (2A-22) is still viable for operations 18 years after launch," said Lt. Col. Dean Holthaus, 2 SOPS director of operations.

Officials said this was only the second time in GPS history that a decommissioned satellite has returned to active status.

The decision to call up the replacement came after controllers determined that the GPS 2A-27 satellite, launched in September 1996, needed to be replaced.

"The vehicle we're replacing has a clock that's malfunctioning," said Capt Frankie Reddick, 2 SOPS assistant director of operations. "When its clock started to show signs of going out, our engineers knew we needed to do something because it wasn't suitable for our global users."

GPS satellites fly about 11,000 nautical miles above the planet and emit continuous navigation signals that allow users to find their precise position in latitude, longitude and altitude and determine time.

The constellation is comprised of six orbital planes with multiple satellites flying in each. The swap of GPS 2A-27 in favor of GPS 2A-22 occurred in Plane B.

While moving GPS 2A-22 from its decommissioned location, the navigation performance was tested. The satellite was declared usable for global users on Tuesday evening.

"We keep on-orbit spares for exactly this purpose," said Lt. Col. Jennifer Grant, 2 SOPS commander. "The robustness of our current constellation and the recent completion of the Expandable 24 architecture provide us with the flexibility to perform replacements like this with minimal impact to global users. Expandable 24 increases global GPS coverage by optimizing the location of GPS satellites in space."