The go-ahead for launch of the U.S. Air Force’s Orbital Test Vehicle (OTV) is on hold pending the review of an “unexpected data signature” emitted during the Oct. 8 launch of Boeing’s GPS IIF-3 satellite on a Delta IV (4,2) rocket.

United Launch Alliance and Pratt & Whitney Rocketdyne are investigating the anomaly, and certification of the OTV launch will not be provided until officials understand the root cause.

The signal was emitted when operators observed reduced thrust of the Pratt & Whitney Rocketdyne RL-10B-2 upper-stage engine, according to the United Launch Alliance, which manufactures and operates the Delta IV and Atlas V boosters (Aerospace DAILY, Oct. 5).

Though OTV was set to launch on an Atlas V late this month while using the RL-10A engine on the upper stage, operators want to be sure there is no common problem that led to the low-thrust performance during last week’s launch.

Despite the reduced RL-10 performance on that flight, the third GPS IIF was sent to its “precise” orbit due to the Delta IV’s “robust system design, flight software, vehicle margins and propellant reserves,” according to ULA.