(AP) -- A government report raising questions about the future reliability of the Global Positioning System satellite network is "overly pessimistic," Air Force commanders said Friday.
A report from the Government Accountability Office, the investigative arm of Congress, said the latest GPS satellite was launched almost 3 1/2 years behind schedule, and further delays could leave the system with fewer than the 24 orbiting satellites it needs as older models wear out and quit working.
Col. David Buckman of the Air Force Space Command at Peterson Air Force Base, Colo., said the report's facts were correct, but "we think it draws overly pessimistic conclusions based on those facts."
Buckman said satellites currently in the design or construction phase are on schedule and the Air Force has 31 healthy, operational satellites in orbit.
Even if the count did drop below 24 - which Buckman said was unlikely - most users, including some military applications, wouldn't be affected, he said.
GPS has become nearly indispensable, with untold numbers of receivers in everything from cars and cell phones to military weapons. The receivers can determine their position, their path and the time of day using signals from the satellites, which are launched and operated by the Air Force.
Col. Bernard Gruber, commander of the GPS Wing at Los Angeles Air Force Base, Calif., estimated that there are 750 million GPS users worldwide.
A May 2009 GAO report cast doubt on whether the Air Force could acquire new satellites in time to prevent an interruption in service as older satellites die.
A follow-up report released Sept. 15 credited the Air Force with making improvements but warned that a delay in launching one of the next-generation satellites could still drop the number of operational orbiting satellites to less than 24.
In a conference call with reporters Friday, Buckman and Gruber acknowledged that the Air Force has no spare satellites ready to launch if an orbiting satellite fails, but they pointed to the fact that the system already has more than it needs in orbit.
"We'd like to have more in the barn, (but) we have very robust constellation on orbit right now that's well above the minimum number that were required to have on orbit," Buckman said.
"I think GPS is extremely strong today," he said.
Explore further: GPS satellites not 'falling out of the sky': Air Force