Air Force receives last GPS IIR satellite

  • Published
  • By Staff Sgt. Don Branum
  • 50th Space Wing Public Affairs
SCHRIEVER AIR FORCE BASE, Colo. (AFPN) --  The Air Force received the last in a series of GPS IIR(M) satellites from Lockheed Martin during an recent fly-out ceremony at the Lockheed Martin facility in Valley Forge, Penn.

"The IIR satellites have been great," said Lt. Col. Doug Schiess, operations officer for the 2nd Space Operations Squadron.  He represented the 50th Space Wing at the ceremony.  "One of the things they've done for us is allowed us to reduce our operations tempo. We used to have to do two supports per day on all GPS satellites, but the IIRs have allowed us to go down to one support per day."

The IIR satellites require less support because they have improved autonomous capabilities. The primary autonomous capability is a IIR redundancy management function, which tracks and manages the satellite's subsystems. Internal tests are run regularly and components can be autonomously swapped if a failure is detected.

The IIR series of satellites also has been more robust. After nearly 11 years since the first IIR satellite was launched, all the IIR satellites remain operational and are still on their primary clocks.

"We have multiple clocks for redundancy on each satellite," Colonel Schiess said. "Our older IIA satellites are on their second or third clocks, but we haven't had to change a clock yet for the IIR satellites." 

This robustness makes the satellites more likely to live beyond their projected design lifetimes, which means more utility for taxpayers' dollars.

When GPS IIR(M)-20 launches this summer, it will be the 19th IIR satellite in orbit. Of those 19 satellites, seven are the newer IIR(M) models, which provide an additional signal called L2C for civilian use and additional military code, or M-code, signals.

"The M-code is a modification that the Air Force asked Lockheed Martin to do after they had the GPS IIR contract," Colonel Schiess said. "The M-code provides anti-jam capability, and as we saw we were going into a jamming environment, we knew we'd need the capability sooner than it would have been available on the GPS IIF satellites." 

Lockheed-Martin specialists, at the request of Air Force officials, pulled some of the satellites that were ready for launch out of storage to add the M-code, flex power and L2C capability.

GPS IIR(M)-20 also will transmit on a frequency called L5, which is primarily designed for aviation safety-of-life applications.

"Lockheed-Martin modified this satellite (per the Air Force's request) to transmit on the L5 frequency so we can demonstrate to the International Telecommunication Union (the United Nations body that governs use of satellite communication frequencies) that we're using the frequency," Colonel Schiess said. "We had to start using the frequency or we'd lose the ability to say it's ours." 

The L5 payload aboard the IIR satellite will provide a demonstration signal that secures exclusive protection of the L5 signal spectrum for U.S. use.

GPS IIR(M)-20 is the last IIR(M) satellite the Air Force received due to the L-5 modification, but it will not be the last IIR(M) satellite to launch. GPS IIR(M)-20 is scheduled to launch from Cape Canaveral Air Force Station June 30. The last IIR(M) satellite to launch, GPS IIR(M)-21, is scheduled for liftoff Sept. 11.

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