CAPE CANAVERAL, Florida, Oct 11 (Reuters) - The U.S. Air Force on Thursday launched an investigation into a glitch with the flight of an unmanned Delta 4 rocket that carried a GPS navigational satellite into orbit last week.
The Global Positioning System 2F spacecraft reached its intended orbit despite a problem with the rocket's upper-stage engine, which is built by Pratt & Whitney Rocketdyne, a unit of United Technologies Corp that is being sold to GenCorp .
Future flights of the Delta 4 rocket are on hold, pending results of the investigation, the Air Force said. The Delta 4 rocket is built by United Launch Alliance, a joint venture of Boeing Co and Lockheed Martin Corp.
General William Shelton, who heads Air Force Space Command, said the Air Force planned a rigorous investigation to determine the root cause of the anomaly with the upper-stage engine.
The Delta 4's second-stage RL10 engine unexpectedly reduced its thrust during the Oct. 4 launch, United Launch Alliance reported after the liftoff from Cape Canaveral Air Force Station in Florida.
"The onboard inertial guidance and flight control systems compensated for the lower thrust conditions and the Delta second stage delivered the satellite to the proper orbit," ULA said in a statement.
ULA and Pratt & Whitney Rocketdyne are also investigating the incident.
The probe could also affect launches involving ULA's Atlas 5 rockets, which use a similar RL10 second-stage engine. An Atlas 5 is scheduled to launch around Oct. 25 with the military's X-37B spacecraft, a robotic miniature space shuttle that has made two prior flights.