Buckman's Twitter comments came in response to GAO testimony May 9 before a subcommittee of the U.S. House Committee on Oversight and Government Reform, which questioned GPS's future performance.

"It is uncertain whether the Air Force will be able to acquire new satellites in time to maintain current ," Christina Chaplain, director of GAO acquisition, said in her testimony.

In another tweet, Buckman admitted there have been space command problems in upgrading GPS, including a satellite launched in March that is still not fully deployed above Earth. The satellite, SVN-49, has been sending "unusual performance data," Buckman said, but the command is troubleshooting it and "making good progress." Buckman and officials at the space command could not be reached for further details.

However, (Global Navigation Satellite System) Web site in early May said the SVN-49's problems could prevent it from being declared healthy for months, if ever.

Buckman also said two satellite programs are underway to update the fleet of GPS satellites. "Agree w/GAO there's a potential risk, but GPS isn't falling out of the sky - we have plans to mitigate risk and prevent a gap in coverage," he added.