The U.S. Air Force and Boeing are testing a fix to correct an electrical problem on the first GPS Block IIF satellite that was launched May 27, 2010, and is now in orbit.

The satellite’s “M” code signal, optimized to reduce jamming for military operations, has been shut off until there is verification that the problem has been solved.

The glitch was discovered during testing of another GPS IIF satellite on the ground, according to program sources.

Air Force Space Command, which oversees GPS operations, declined to discuss the issue. However, the government released a notice to GPS users April 6 acknowledging that “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 vehicle will continue to operate within operational specifications and provide the operational signals at current accuracy and power levels to users,” the notice said.

Declining to comment on the electrical problem, Boeing spokeswoman Angie Yoshimura says, “Boeing IIF spacecraft continue to meet all performance specifications and perform as designed. . . . As we continue to produce the GPS IIF satellites, ongoing analysis and tests are conducted. This is a normal and expected activity for any satellite constellation in production.”

The electrical issue is not the first problem for the GPS IIF since it reached orbit. Air Force Lt. Gen. (ret.) Tom Sheridan, who recently retired as program executive officer for the service’s space programs, last year slipped launch of the second GPS IIF pending a fix to the cross-links for the nuclear-detection payload. This system warns of a nuclear blast, and the cross-links were experiencing degradation. The second satellite is scheduled to launch July 14 with a software fix for the cross-link problem.

Last summer, Air Force officials acknowledged that navigation and timing signals from the IIF were operating within specifications, though German aeronautics and space center officials detected residual errors when combining three main signals—L1, L2 and L5—from the satellite.

Meanwhile, Boeing is offering to continue GPS IIF production beyond the 12 on order for the Air Force, despite a decision by the service to move on to the Lockheed Martin GPS IIIA program. Roger Krone, president of Boeing Network and Space Systems, says the company is willing to maintain the existing prices for further sales of GPS IIF satellites to the Air Force. The program suffered problems during development, costing Boeing.

Pricing for the first nine satellites was fixed about 10 years ago. Air Force officials say the average contracted price of a GPS IIF is $121 million, although the first satellites cost more than $300 million to build.

To save time and money, Boeing has established a pulse production line for the GPS IIF in El Segundo, Calif. It draws upon the company’s experience building large numbers of commercial and military aircraft.