The Propulsion Directorate was formed through the merger of the aerospace propulsion section at Wright Laboratory and the space propulsion section at Phillips Laboratory. Each section, both before and after the merger, has played a significant role in past and present propulsion systems. Prior to the development of Project Apollo by NASA, the Air Force worked on the development and testing of the F-1 rocket engine used to power the Saturn V rocket. The facilities for testing rockets are frequently used for testing new rocket engines including the RS-68 rocket engine developed for use on the Delta IV launch vehicle. The space propulsion area also develops technologies for use in satellites on-orbit to alter their orbits. An AFRL-developed experimental Electric Propulsion Space Experiment (ESEX) arcjet was flown on the ARGOS satellite in 1999 as part of the Air Force Space Test Program.