has developed “optimized transmitter settings” for the GPS IIF spacecraft to support reactivation of the M-code (or military-specific signal), according to an industry official.
The U.S. Air Force switched off the M-code on the first GPS IIF spacecraft, which was launched May 27, 2010, owing to discoveries related to signal strength during factory testing (Aerospace DAILY, June 21).
When the first IIF “entered operational service, the Air Force configured the vehicle with all signals, operating at power levels far exceeding specification and with the M-code enabled to support developmental testing of this non-operational code,” according to an industry official. “While the L1 transmitter continues to perform well, without failure, on all IIF satellites in production and on-orbit, the ongoing factory testing has indicated that operation of the transmitter at power levels that are lower, but still in excess of specification, may provide the optimum utilization of the IIF satellite’s capability over its mission life.”
This official refutes the notion that this is an electrical problem on the satellites and says the spacecraft in orbit is “meeting all operational requirements, with the best atomic clock performance ever seen on-orbit.” The official declined to be identified, as the Air Force has yet to comment on the issue.
The government released a notice to GPS users April 6 acknowledging “the government is accomplishing testing that requires the non-operational M-code signal on SVN 62 (PRN 25) [which is the first IIF] be turned off for an indeterminate period.”
The Air Force turned off the M-code in part “because there is not current user requirement for the M-code military signal,” the industry official says. “This signal was turned off in April 2011 so that the total power level of the L1 transmitter would be reduced.”
Operational signals on the GPS IIF in orbit “continue to operate at the same power levels, and all the satellite operations are nominal and in full support of the mission with no impact to operational users,” the industry official adds. The Air Force has not said when it will switch the M-code back on for the first IIF satellite.
Boeing spokeswoman Diana Ball says the company received a rating of “excellent” in the last award fee notification for GPS IIF performance. The second GPS IIF satellite is at Cape Canaveral being prepared for a July 14 launch.