WASHINGTON — The launch of a U.S. Air Force X-37B reusable spaceplane has been delayed until Nov. 13 due to an ongoing Delta 4 Anomaly”>investigation into a glitch that occurred during an earlier launch on a different rocket, United Launch Alliance (ULA) said in an Oct. 19 press release.

The launch of the robotic X-37B was scheduled for Oct. 25 atop ULA’s Atlas 5 rocket but was postponed as ULA and the Air Force continued to review an upper-stage thrust anomaly that took place during the successful Oct. 4 launch of the GPS 2F-3 satellite aboard a ULA Delta 4 rocket, according to the press release. Denver-based ULA is a Boeing-Lockheed Martin joint venture.

The Atlas 5 and Delta 4 rockets use different variants of the RL-10 upper stage built by Pratt & Whitney Rocketdyne of Canoga Park, Calif. The Air Force has created an “accident investigation board” to review what happened, while ULA and Pratt & Whitney Rocketdyne are conducting their own investigation.

Telemetry showed lower-than-expected performance of the Delta 4’s RL-10 upper-stage engine during the launch of the GPS 2F-3 satellite from Cape Canaveral Air Force Station in Florida. 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.

The X-37B mission is called Orbital Test Vehicle-3 because it is the program’s third spaceflight. The details of the mission are classified.