AS-203 was an unmanned flight of the Saturn IB rocket on July 5, 1966, also the first launch of a Saturn IB from Pad 37B. 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 successfully achieved its objectives, but the stage was inadvertently destroyed after four orbits.
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| NASA cachet for Saturn IB AS-203 with KSC machine and hand cancel, July 5, 1966. |
The flight also investigated 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 put the spacecraft into a parking Earth orbit, before restarting the engine for flight to the Moon.
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| "Kennedy Space Center, Fla. - The Saturn booster A/S 203 is erected on Complex 37 at Cape Kennedy. The booster will undergo extensive checkouts before being launched in the third quater of this year. This will be the first flight from Complex 37 since its modification to launch the Saturn 1B vehicle. NASA Photo. April 18, 1966." |
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| Saturn IB AS-203 Spacecraft Swanson cachet cover with Cape Canaveral postmark July 5, 1966. |
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| AS-203 and AS-202 dual Cape Canaveral dual postmarks Velvatone cover. |
