While the GPS IIIF-3 satellite was launched successfully on 4 October, later analysis showed that the upper stage engine had a reduced thrust level on the RL10 engine. The onboard flight control systems compensated for the lower thrust levels allowing the satellite to achieve the correct orbit. An investigation into the anomaly has found that the fuel leak was within the RL10 thrust chamber. The leak apparently began during the first engine start sequence of the launch.
Future launches using RL10 engines on their upper stages including the Atlas V501 launch of the X-37B/OTV 1 (FLIGHT 2) mini-space plane for the US Air Force are having special boroscope inspections of engine compartments.
