On July 5, 1966, the first Apollo orbital mission, AS-203 was launched from NASA’s Kennedy Space Center, Florida. It was an uncrewed flight of the vehicle’s second stage, the S-IVB stage (it was the 3rd stage of Saturn V, which carried humans to the Moon), to test it under orbital conditions and to obtain flight information on venting and chill-down systems, fluid dynamics, and heat transfer of propellant tanks, attitude and thermal control system, launch vehicle guidance, and checkout in orbit.

During the fourth orbit, internal pressures built up in the S-IVB stage while a pressure differential test was being performed. The pressures built up well in excess of design values and the stage fragmented. Despite that, all mission objectives were achieved.

Today’s (July 5) story of what happened this day in Science, Technology, Astronomy, and Space Exploration history.

AS-203, the first Apollo orbital mission

The Apollo AS-203 mission was an uncrewed test of the vehicle’s second stage, the S-IVB stage, and the instrument unit of the Saturn V to obtain flight information under orbital conditions. The configuration of the Saturn IB was designed to match the Saturn V as closely as possible. NASA’s Marshall Space Flight Center designed, developed, and managed the production of the Saturn I and the mighty Saturn V rocket that took astronauts to the moon.

After the launch, the S-IVB and Instrument Unit (IU) were inserted into a 100-nautical-mile (190 kilometers or 120 miles) circular orbit with a period of 88.21 minutes and an inclination of 31.94 degrees around Earth.

The S-IVB engine burned once in the Earth’s atmosphere, just over two minutes, and then was shut down. The engine’s capability to restart after the coast was demonstrated. Flight information was obtained on venting and chill down systems, attitude and guidance control, thermal control, and performance of the propellant tanks.

Two cameras were mounted to take photos to record the behavior of the liquid hydrogen fuel in the tanks They also photographed the stage separation.

After completing the filming, the camera pods ejected from the stage and parachuted into the Atlantic Ocean. Recovery forces retrieved only one of the pods from the ocean but the film provided dramatic footage of the ignition of the second stage engine.

AS-203 launch
On July 5, 1966, the AS-203 rocket launched from NASA’s Kennedy Space Center. It was the first Apollo orbital mission. Photo: NASA

During the first two orbits around Earth, the S-IVB design test objectives were carried out and the hydrogen was found to behave mostly as predicted, with sufficient control over its location and engine temperatures required for restart.

The next two orbits were used for extra experiments to obtain information for use in future cryogenic stage designs. These included

  • a free-coast experiment to observe and control the negative acceleration of the fuel caused by the small amount of aerodynamic drag on the vehicle
  • a rapid fuel tank depressurization test
  • and a closed fuel tank pressurization test.

The closed fuel tank experiment involved pressurizing the hydrogen tank by closing its vents while depressurizing the oxygen tank by allowing it to continue venting. It was expected that the pressure difference between the two tanks (measured as high as 39.4 pounds per square inch (272 kPa) would collapse the common bulkhead separating them, as happened in a ground test.

The rupture must have occurred during the two-minute loss of signal between the Manned Spacecraft Center and the Trinidad tracking station. The Trinidad radar image indicated the vehicle was in multiple pieces, and telemetry was never re-acquired. NASA concluded that a spark or impact must have ignited the propellants, causing an explosion.

Despite the destruction of the stage, the mission was classified as a success, having achieved all of its primary objectives and validating the design concept of the restartable S-IVB-500 version.

The tests gave managers confidence that the engine would perform as expected during the first flight of the Saturn V rocket, flown as Apollo 4 in 1967. In September 1966, the Douglas Aircraft Company, which built the S-IVB, declared that the design was ready for use on the Saturn V rocket to send humans to the Moon.

July 5 in Science, Technology, Astronomy, and Space Exploration history


M. Özgür Nevres

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