UPDATED Oct. 12, 5:30 EDT

WASHINGTON — U.S. Air Force Gen. William Shelton, commander of Air Force Space Command, has ordered an “accident investigation board” to review an upper-stage thrust anomaly that occurred during the successful Oct. 4 launch of a GPS satellite aboard a United Launch Alliance (ULA) Delta 4 rocket, the service announced Oct. 11.

Meanwhile, ULA said Oct. 5 that the scheduled Oct. 25 launch of the Air Force’s X-37B reusable military spaceplane is on hold while ULA and upper-stage engine maker Pratt & Whitney Rocketdyne investigate the cause of the anomaly. The robotic X-37B is slated to launch atop ULA’s Atlas 5 rocket, whose RL-10 upper-stage engine is similar to the one used on the Delta 4.

Shelton’s investigation is separate from the one ULA and Pratt & Whitney Rocketdyne are conducting, Maj. Tracy Bunko, an Air Force spokeswoman, said Oct. 12.

Denver-based ULA, a Boeing-Lockheed Martin joint venture, said telemetry showed lower-than-expected performance of the Delta 4’s RL-10 upper stage during the GPS 2F launch from Cape Canaveral Air Force Station, Fla. The rocket’s guidance system and flight computers compensated for the lower thrust, delivering the Boeing-built navigation satellite to its proper orbit with the help of reserve fuel, ULA said.

ULA and the Air Force must determine the cause of the glitch before they can proceed with the launch of the X-37B on what will be that program’s third flight to date, the ULA press release said. Details of the so-called Orbital Test Vehicle-3 mission are classified.

Pratt & Whitney Rocketdyne of Canoga Park, Calif., builds different versions of the RL-10 for the Delta 4 and Atlas 5, the workhorse launch vehicles of the U.S. Department of Defense.

The results of the Air Force-ordered investigation will be presented to Shelton before being made public, the service said.