AS-203 (or SA-203) was an uncrewed flight of the

Saturn IB The Saturn IB (also known as the uprated Saturn I) was an American launch vehicle commissioned by the National Aeronautics and Space Administration (NASA) for the Apollo program. It uprated the Saturn I by replacing the S-IV second stage (, 43 ...

rocket on July 5, 1966. It carried no

command and service module The Apollo command and service module (CSM) was one of two principal components of the United States Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functioned as a mother sh ...

, as its purpose was to verify the design of the

S-IVB The S-IVB (pronounced "S-four-B") was the third stage on the Saturn V and second stage on the Saturn IB launch vehicles. Built by the Douglas Aircraft Company, it had one J-2 rocket engine. For lunar missions it was fired twice: first for Earth ...

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 stage was inadvertently destroyed after four orbits.

Objectives

The purpose of the AS-203 flight was to investigate the effects of weightlessness on the

liquid hydrogen Liquid hydrogen (LH2 or LH2) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully l ...

fuel in the

-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 Saturn V is a retired American super heavy-lift launch vehicle developed by NASA under the Apollo program for human exploration of the Moon. The rocket was human-rated, with multistage rocket, three stages, and powered with liquid-propellant r ...

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. In order to keep residual propellants in the tanks on orbit, there would be no

payload as there was on

AS-201 AS-201 (or SA-201), flown February 26, 1966, was the first uncrewed test flight of an entire production Block I Apollo command and service module and the Saturn IB launch vehicle. The spacecraft consisted of the second Block I command module ...

and

AS-202 AS-202 (also referred to as SA-202) was the second uncrewed, suborbital test flight of a production Block I Apollo command and service module launched with the Saturn IB launch vehicle. It was launched on August 25, 1966, and was the first fl ...

. This was replaced by an aerodynamic

nose cone A nose cone is the conically shaped forwardmost section of a rocket, guided missile or aircraft, designed to modulate oncoming airflow behaviors and minimize aerodynamic drag. Nose cones are also designed for submerged watercraft such as ...

. Also, the full load of

liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an app ...

oxidizer An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxi ...

was shorted slightly so that the amount of hydrogen remaining would approximate that of the Saturn V parking orbit. The tank was equipped with 88 sensors and two TV cameras to record the fuel's behavior. This was also the first launch of a Saturn IB from Pad 37B.

Preparation

In the spring of 1966, the decision was made to launch AS-203 before

, as the CSM that was to be flown on AS-202 was delayed. The S-IVB stage arrived at Cape Kennedy 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 regimen ran into problems that had plagued AS-201, including cracked solder joints in the printed-circuit boards, requiring over 8,000 to be replaced. In June 1966, three Saturn rockets could be seen set up on various pads across the Cape: at Pad 39A was a full-size mock-up of the Saturn V; AS-202 was at Pad 34; and AS-203 was at 37B.

Flight

The rocket launched on the first attempt on July 5. The

and Instrument Unit (IU) were inserted into a 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 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 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 The Lyndon B. Johnson Space Center (JSC) is NASA's center for human spaceflight (originally named the Manned Spacecraft Center), where human spaceflight training, research, and flight control are conducted. It was renamed in honor of the late U ...

and the

Trinidad Trinidad is the larger and more populous of the two major islands of Trinidad and Tobago. The island lies off the northeastern coast of Venezuela and sits on the continental shelf of South America. It is often referred to as the southernmos ...

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. In September

Douglas Aircraft Company The Douglas Aircraft Company was an American aerospace manufacturer based in Southern California. It was founded in 1921 by Donald Wills Douglas Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas; it then operated a ...

, which built the S-IVB, declared that the design was ready for use on the Saturn V to send men to the Moon.

References

External links

AS-203 Launch Video

NASA Space Science Data Coordinated Archive
* ttp://www.hq.nasa.gov/office/pao/History/SP-4205/cover.html Chariots for Apollo: A History of Manned Lunar Spacecraft {{Use American English, date=January 2014 Apollo program Spacecraft launched in 1966 Test spaceflights Spacecraft launched by Saturn rockets