AS-203: NASA’s Odd Apollo Mission

As 1966 began, NASA and its contractors were pushing forward with the first test flights of actual Apollo hardware in hopes of launching the first manned mission by year’s end. On January 20, the final launch abort test, designated A-004, was successfully flown at the White Sands Missile Range in New Mexico (see “The First Launch of Apollo Flight Hardware”). But unlike the previous launch abort tests which used boilerplate models of the Apollo Command Module (CM), this was the first flight to use actual flight hardware – North American Aviation’s CM-002 spacecraft. On February 26, NASA launched the Apollo Command/Service Module (CSM) on its first test flight into space from Cape Kennedy in Florida (which reverted to its original name of Cape Canaveral in 1973). Designated AS-201, this first flight of the new Saturn IB sent CSM-009 on a 37-minute suborbital mission which ended with the successful recovery of the CM in the Atlantic (see “The First Flight of the Apollo-Saturn IB”).

The launch of Apollo AS-201 from LC-34 on February 26, 1966. (NASA)

Although the AS-201 mission met all of its objectives, the flight did uncover a number of issues with the Apollo CSM which needed to be resolved before the next mission designated AS-202 could fly. In order to keep program on schedule, in April 1966 NASA officials announced that they would launch the next Apollo mission, AS-203, out of sequence. Unlike the other Apollo test flights, the objectives of AS-203 centered on testing Saturn launch vehicle hardware. As a result, this rather odd Apollo mission consisted of just a Saturn IB rocket and did not include an Apollo spacecraft at all.

The AS-203 Objectives

The primary piece of hardware for the Apollo AS-203 mission was the Saturn IB rocket designated SA-203. The Saturn IB was a substantially improved version of the Saturn I originally developed by the team led by famed rocket engineer Wernher von Braun and based at NASA’s Marshall Space Flight Center in Huntsville, Alabama. The first stage of this new launch vehicle, built by Chrysler and designated S-IB, was an updated version of the S-I stage successfully flown ten times between 1960 and 1965 during the Saturn I test flight program (see “The Last Launch of the Saturn I”). Like the S-I stage, the S-IB structure consisted of a set of eight 1.8-meter in diameter tanks holding LOX and RP-1 derived from the proven Redstone rocket clustered around a single 2.7-meter LOX tank adapted from the Jupiter rocket. A new set of eight swept-back fins as well as a host of other changes to the hardware and fabrication of the S-IB made it 9,000 kilograms lighter than the older S-I. The S-IB was powered by eight improved Rocketdyne H-1 engines whose total thrust was increased from 6,683 to 7,120 kilonewtons.

Cutaway diagram showing the major components of the S-IB stage. Click on image to enlarge. (NASA)

By far the biggest change in the transition from Saturn I to IB was in the second stage designated S-IVB built by the Douglas Aircraft Company. Instead of six Pratt & Whitney RL-10 engines which produced a total of 400 kilonewtons of thrust on the S-IV stage used by the Saturn I, the new and larger S-IVB stage employed a single Rocketdyne J-2 engine to produce 890 kilonewtons of thrust using the same high energy propellant combination of liquid hydrogen and LOX utilized by the S-IV.

Cutaway diagram showing the major components of the S-IVB stage. Click on image to enlarge. (NASA/MSFC)

In addition to increasing the lift capacity of the Saturn IB so that it could carry the CSM or LM (Lunar Module) into Earth orbit for initial test flights, early launches of the Saturn IB also allowed flight testing of the nearly identical version of the S-IVB stage that would be employed as the third stage of the Saturn V which would send Apollo to the Moon. The S-IVB stage was topped off by the 2,100-kilogram, ring-shaped Instrument Unit (IU) which controlled the Saturn rocket during its flight. The Saturn IB, without the payload, stood 43.2 meters tall and was capable of placing about 21 metric tons of payload into low Earth orbit. The total height of the Apollo-Saturn IB was 68.3 meters and it had a lift off mass of 598 metric tons.

This chart compares the Saturn I, IB and V rockets used in the Apollo program. (NASA)

The objectives of the Apollo AS-203 mission centered on the Saturn IB rocket and especially the S-IVB stage it shared with the Saturn V Moon rocket. The primary objectives included evaluating the S-IVB and IU in orbital flight like that it would experience while in Earth parking orbit during a lunar mission. The behavior of liquid hydrogen inside the S-IVB fuel tank would be observed using a pair of TV cameras to verify the effect of various tank design elements. The J-2 engine would also be put through its paces to simulate an in-orbit restart as it would do during a Saturn V flight.

Schematic showing the configuration of the Saturn IB for the AS-203 mission. Click on image to enlarge. (NASA)

Since the Apollo spacecraft was not required for this flight, SA-203 was topped off by a simple 1,680-kilogram aerodynamic nose cone which remained attached to the S-IVB during the entire AS-203 mission. In addition to instrumentation to support the mission, this nose cone housed an experiment to verify how cryogenic liquid nitrogen would behave under weightless conditions in support of future fuel cell system development. Liquid nitrogen was chosen to serve as a surrogate for LOX, which would normally be used as a reactant by fuel cells, because of its similar properties and it was safer to handle.

Diagram showing the top of the nose cone for the AS-203 mission and the placement of the cryogenic nitrogen experiment. Click on image to enlarge. (NASA)

In order to lighten the Saturn IB further to maximize the amount of liquid hydrogen remaining in the stage’s tank once orbit was achieved, the S-IVB stage on SA-203, designated S-IVB-203, carried a light load of LOX – 53,800 kilograms versus its normal load of 86,600 kilograms. This cut the normal 7½-minute burn time of the S-IVB stage down to about four minutes and 50 seconds guaranteeing that at least 8,400 kilograms of liquid hydrogen would remain in the S-IVB stage after it reached orbit. The estimated mass of the S-IVB stage, the nose cone and other equipment once in orbit was 26,550 kilograms, including residual propellants, making this the heaviest object ever orbited by the US up to this time. At lift off, SA-203 stood 52.7 meters tall and had a launch mass of 538 metric tons – the lightest Saturn IB that would ever be launched.

Diagram showing the configuration of the S-IVB-203 stage flown on the AS-203 mission. Click on image to enlarge. (NASA)

Since the S-IVB-200 stage used on this mission differed in some key aspects from the S-IVB-500 model to be used by the Saturn V, a number of modifications had to be made to support the AS-203 mission. Both versions of the S-IVB stage included an Auxiliary Propulsion System (APS) to control roll as the J-2 engine burned and to maintain attitude during coasting flight in orbit. The APS consisted of a pair of modules protected by aerodynamic fairings near the base of the stage housing a trio of 670-newton engines as well as the tankage for their hypergolic propellants. The APS on the S-IVB-500 model was enlarged compared to the -200 model to handle the larger payload and up to 4½ hours of coasting flight in Earth parking orbit. It also included a pair of 310-newton ullage engines to help keep the stage’s propellants settled in their tanks during the weightless coast in orbit.

This diagram shows the major components of the gaseous oxygen venting system used to help settle the propellants in the tanks of the S-IVB-203 stage. Click on image to enlarge. (NASA)

To provide this ullage function on the AS-203 mission, the S-IVB-203 stage was fitted with a pair of rear-facing nozzles which expelled gaseous oxygen produced by the evaporation of the estimated 1,700 kilograms of residual LOX in its tank. The 130 newtons of thrust produced by this system combined with the minimum of 30 newtons from the continuous venting of excess gaseous hydrogen would produce enough ullage to meet the objectives of this mission which was expected to last about four orbits.

A schematic of the chill down and recirculation system employed by the J-2 engine on the S-IVB-203 stage. Click on image to enlarge. (NASA)

Another major objective of this mission in support of Saturn V development was the simulated restart of the J-2 engine as would be done to boost the Apollo out of its temporary Earth parking orbit and on its way to the Moon. For this test, the J-2 engine on S-IVB-203 was fitted with a chill down and recirculation system like that to be employed on the S-IVB-500 model. This system would use the cryogenic propellants to prechill the J-2 engine and its associated systems for five minutes prior to ignition. It was decided that an actual reignition of the J-2 would not be attempted on this flight. Doing so would have required an extra 1,800 kilograms of LOX as well as 1,400 kilograms of additional equipment which would have compromised meeting other mission objectives. Based on the engineers’ experience with J-2 engine ground testing, it was felt that a restart test in orbit was not as useful as meeting those other objectives. The AS-203 mission would end with the purposeful overpressurization of the liquid hydrogen tank until the common bulkhead with the LOX tank failed. This was done to verify the results from failure testing done on the ground. Naturally, no recovery of any of the orbiting hardware would be attempted.

The AS-203 Flight

The first major piece of hardware to arrive at Cape Kennedy for the Apollo AS-203 mission was the S-IVB-203 second stage delivered on April 6, 1966. The first stage of the Saturn IB, serial number S-IB-3, arrived by barge on April 12. The S-IB stage was erected six days later on the newly modified Pad B at Launch Complex 37 which had previously been used to support the last Saturn I launch almost nine months earlier (see “From Apollo to Orion: Space Launch Complex 37”). The lone pad at LC-34 which was used for the AS-201 mission had already been occupied since March 4 by the Saturn IB rocket meant for the AS-202 mission so it was not available for the AS-203 mission. On April 21, the S-IVB stage was added to the stack followed by the IU and nose cone later that same day. Initial power was applied to the S-IB stage on April 25 as a long series of pre-launch tests commenced.

SA-203 on Pad B at Launch Complex 37 being prepared for launch. (NASA)

With the completion of the flight readiness test on June 27, RP-1 tanking operations for the S-IB for the countdown demonstration test (CDDT) began the following day. The first part of the CDDT was completed on June 29 while the second was done on July 1. With this last key pre-launch test completed, the decision was made to pick up the countdown at T-11 hour 30 minutes at 7:30 PM EDT on July 4 for a launch at 9:00 AM the next morning.

Kennedy Space Center Director Kurt Debus (left) and Wernher von Braun at the periscope in the LC-37 blockhouse during the AS-203 countdown. (NASA)

The countdown for AS-203 went smoothly until 8:45 AM EDT on July 5, 1966 when a hold was called at T-15 minutes. This gave ground controllers time to catch up with some tasks and investigate a transmission failure in one of the two TV cameras that was to observe the liquid hydrogen in the S-IVB fuel tank. After a delay of almost an hour and a half with no resolution to the TV camera issue, it was decided to recycle the countdown to T-15 minutes and launch with just one operating camera. After an additional two-minute hold just three minutes before launch to verify the status of the radar at the Bermuda tracking station, AS-203 finally lifted off from LC-37B at 10:53:17 AM EDT.

The launch of Apollo AS-203 from LC-37B on July 5, 1966. (NASA)

With its relatively low launch weight, SA-203 accelerated faster than usual hitting Mach 1 at an altitude of 6.67 kilometers after just 51.6 seconds of flight – 12.9 seconds faster than the earlier flight of SA-201. The S-IB stage continued to give a near nominal performance with separation of the S-IVB stage coming only 0.8 seconds early at 143.4 seconds after launch. Afterwards, a pair of camera pods which had filmed the stage separation were ejected from the spent S-IB stage but only one of them was recovered from the Atlantic. A near-nominal performance of the S-IVB stage followed with engine cut off only 2.9 seconds early after a total of 7 minutes and 13 seconds of powered flight from both stages. The S-IVB-203 stage, now carrying the international satellite designation of 1966-059A, was in a 185.4 by 189.3 kilometer orbit with an inclination of 32.0° – just a touch below the 190-kilometer circular orbit desired. With an estimated 8,633 kilograms of liquid hydrogen left in its fuel tank for its tests, the Saturn IB had performed admirably for its first orbital launch.

A frame from the video returned from the TV camera observing the behavior of the liquid hydrogen in the S-IVB tank. (NASA)

During the first orbit, the sole operating TV camera at the top of the S-IVB fuel tank successfully observed the response of the liquid hydrogen as various venting combinations were employed to settle the fuel in its tank. The behavior of the cryogenic liquid hydrogen as well as its interactions with various baffles, screens and other elements in the tank were as predicted (see the Related Video section below for actual footage from inside of the S-IVB-203 liquid hydrogen tank). The simulated restart of the J-2 engine during the subsequent orbit verified the operation of the chill down and recirculation systems that would be used by the S-IVB-500 model. Other test objectives were also met including the successful operation of the IU and the APS in orbit for the first time. These successful tests of key S-IVB systems help to improve officials’ confidence in the decision to fly with three live stages for the first test flight of the Saturn V scheduled for 1967 (see “Apollo 4: The First Flight of the Saturn V“).

This map shows the track network support for the AS-203 mission. Click on image to enlarge. (NASA)

By the start of the fourth orbit, the near continuous venting to settle the stage’s residual propellants had raised the orbit to 202.4 by 216.9 kilometers. With the successful completion of all of the other mission objectives, the final test was started. The vents on the liquid hydrogen tank were closed while at the same time those of the LOX tank were all opened to reduce its internal pressure. As the liquid hydrogen boiled, it increased the pressure differential across the common bulkhead between the two propellant tanks. About six hours and 20 minutes after launch near the beginning of the fifth orbit, the tracking station at Kennedy Space Center received the last telemetry from the S-IVB-203 stage as it moved out of range. Two minutes later, when the stage was suppose to be picked by the NASA tracking facility on Trinidad, radar only detected a debris cloud. Subsequent study of the telemetry confirmed the bulkhead failure and destruction of the S-IVB stage had occurred at about the same pressure differential as had happened during ground testing.

The remains of the disintegrated S-IVB stage quickly fell out of orbit over the Caribbean bringing the AS-203 mission to an end. With the successful completion of the AS-203 mission and with all of its primary as well as secondary objectives met, efforts focused on getting the AS-202 mission off the ground in August for what was suppose to be the final unmanned test flight of the Apollo spacecraft before the start of manned flights (see “AS-202: The Last Test Flight Before Apollo 1“). And with this, the US was yet one step closer towards reaching its lunar landing goal.

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Related Video

This is a quarterly film report produced by NASA MSFC about the status of the Saturn IB program during the July to September 1966 period including the AS-203 mission

Here is some footage from NASA of the launch of AS-203 from LC-37B on July 5, 1966.

Here is a recording of selected parts of the video feed from the TV camera observing the liquid hydrogen inside the tank of the S-IVB-203 stage flown on the AS-203 mission.

Here is a diagram showing the placement of the TV camera on top of the fuel tank on S-IVB-203 as well as the position of key interior structures and fiducial marks seen in the video.

Diagram showing the placement of the TV camera in the fuel tank of the S-IVB-203 stage. Click on image to enlarge. (NASA)

Related Reading

“The First Flight of the Apollo-Saturn IB”, Drew Ex Machina, February 26, 2016 [Post]

“The Last Launch of the Saturn I”, Drew Ex Machina, July 30, 2015 [Post]

“From Apollo to Orion: Space Launch Complex 37”, Drew Ex Machina, December 5, 2014 [Post]

General References

Roger E. Bilstein, Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles, University Press of Florida, 2003

Alan Lawrie, Saturn I/IB The Complete Manufacturing and Testing Records, Apogee Books, 2008

Richard W. Orloff and David M. Harland, Apollo: The Definitive Sourcebook, Springer-Praxis, 2006

Saturn Flight Evaluation Working Group, Results of the Second Saturn IB Launch Vehicle Test Flight AS-203, MPR-SAT-FE-66-12, NASA Marshall Space Flight Center, September 22, 1966

“Saturn/Apollo Uprated Saturn I (Second Mission)”, NASA Press Release 66-157, June 26, 1966