AS-203: Difference between revisions

{{Infobox Space missionspaceflight

|apogee COSPAR_ID = {{convert|100|nmi|km}}1966-059A

|orbits mission_duration = 4~6 hours

|period orbits_completed = 88.5 min 4

'''AS-203''' (oralso known as '''SA-203''' or ‘’’Apollo 3’’’) was an unmanneduncrewed flight of the [[Saturn IB]] rocket on July 5, 1966. It carried no [[Apollocommand Command/Serviceand Moduleservice module]] spacecraft, 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.

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 put the spacecraft into a parking Earth 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.<ref name=NASAreport>{{Citation

| url = httphttps://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680012073_1968012073.pdf

In order to keep residual propellants in the tanks on orbit, there would be no [[Apollocommand Command/Serviceand service Modulemodule]] payload as there was on [[AS-201]] and [[AS-202]]. This was replaced by an aerodynamic [[nose cone]]. Also, the full load of [[liquid oxygen]] [[oxidizer]] was shorted slightly so that the amount of hydrogen remaining would approximate that of the Saturn V parking orbit.<ref name=NASAreport/> The tank was equipped with 88 sensors and two TV cameras to record the fuel's behavior.

This was also the first flight of a new type of Instrument Unit that controlled the Saturn rockets during launch, and also the first launch of a Saturn IB from [[Cape Canaveral Air Force Station Space Launch Complex 37|Pad 37B]].

In the spring of 1966, the decision was made to launch AS-203 before [[AS-202]], as the CSM that was to be flown on AS-202 was delayed. The S-IVB stage arrived at [[Cape Canaveral Air Force Station|Cape CanaveralKennedy]] on 6 April 1966; the S-IB first stage arrived six days later, and the Instrument Unit came two days after that.

On April 19, technicians began to erect the booster at Pad 37B. Once again, the testing regimeregimen ran into problems that had plagued AS-201, including cracked solder joints in the printed-circuit boards, requiring over 8,000{{clarify|reason=Probably not 8000 circuit boards, maybe 8000 solder joints? If so, then "replaced" isn't the correct word. "Reworked"?|date=May 2024}} to be replaced.

The rocket launched on the first attempt on July 5. The [[S-IVB]] and [[Saturn V instrument unit|Instrument Unit]] (IU) were inserted into a {{convert|100|nmi|km mi|adj=on}} circular orbit.

The S-IVB design test objectives were carried out on the first two orbits, and the hydrogen was found to behave mostly as predicted, with sufficient control over its location and of engine temperatures required for restart. The next two orbits were used for extra experiments to obtain information offor 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 {{convert|39.4|psi|kPa}}) would collapse the common bulkhead separating them, as confirmedhappened in a ground test. The rupture must have occurred during the two-minute loss of signal between the [[Lyndon B. Johnson Space Center|Manned Spacecraft Center]] and the [[Trinidad]] [[Missile Test Project#Tracking Stationsstations|tracking station]],. whereThe Trinidad radar acquiredimage indicated the vehicle was in multiple pieces, indicatingand antelemetry explosionwas hadnever occurredre-acquired. It isNASA believedconcluded 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 dashS-IVB-500 version. In September [[Douglas Aircraft Company]], whowhich built the S-IVB, declared that the stagedesign was operational and couldready befor useduse on the Saturn V to send men to the Moon.

[[deCategory:AS-203Saturn IB]]