AS-203

AS-203 (also known as SA-203 or Apollo 3) was an uncrewed flight of the Saturn IB rocket on July 5, 1966. It carried no command and service module, as its purpose was to verify the design of the S-IVB rocket stage restart capability that would later be used in the Apollo program to boost astronauts from Earth orbit to a trajectory towards the Moon. It achieved its objectives, but the S-IVB was inadvertently destroyed after four orbits during a differential pressure test that exceeded the design limits.

==Objectives== The purpose of the AS-203 flight was to investigate the effects of weightlessness on the liquid hydrogen fuel in the S-IVB-200 second-stage tank. The lunar missions would use a modified version of the S-IVB-200, the S-IVB-500, as the third stage of the Saturn V launch vehicle. This called for the stage to fire briefly to insert the spacecraft into an Earth parking orbit, before restarting the engine for flight to the Moon. In order to design this capability, engineers needed to verify that the anti-slosh measures designed to control the hydrogen's location in the tank were adequate, and that the fuel lines and engines could be kept at the proper temperatures to allow engine restart.