For long time space enthusiasts like myself, the test flights of the Orion and other new crewed spacecraft in recent years is reminiscent of the first Apollo test flights. But unlike today’s spacecraft builders who have the benefit of decades of engineering advances and a stable of proven space-rated technologies, designing and building Apollo pushed the limits of technology like no other spacecraft built before. In fact it can be easily argued that none of today’s new crewed spacecraft would be design, built and flight qualified as readily without the benefit of the experience with Apollo.

Because of the innovative nature of the Apollo spacecraft and the new technologies it employed, many test flights were required to verify the hardware design. This was especially true in this age of primitive computers and engineers performing calculations by hand using slide rules which limited the sophistication of “simulations” used to test every aspect of spacecraft design. After years of work, the very first test of a production model Apollo spacecraft during an actual spaceflight was launched a half century ago on an unmanned mission known as AS-201.

A New Spacecraft

The Apollo AS-201 mission was not the first test flight of the Apollo program. Starting with the Apollo A-101 mission in May 1964, NASA launched a total of five Apollo-related payloads into orbit on Saturn I development flights over the course of 15 months (see “50 Years Ago Today: The First Apollo Orbital Test Flight”). Although the mission hardware consisted of instrumented boilerplate models of the CSM (Command-Service Module), they gathered vital data on the aerodynamic and structural properties of the Apollo spacecraft during actual flight. The separation of Apollo’s Launch Escape System (LES) during flight was also tested during these missions.

Boilerplate models of the Apollo CM (Command Module) were also used in a series of launch abort tests starting in November 1963. These included pad abort tests with just the LES and CM as well as flights using the Little Joe II rocket to test the LES under much more stressing flight conditions (see “50 Years Ago Today: The First Flight of the Apollo Little Joe II”). This flight test program culminated in the Apollo A-004 mission launched on January 20, 1966. For the first time, production Apollo flight hardware was launched on a mission this time to test the LES and the second production Apollo, designated CM-002, under a stressing tumbling abort situation (see “The First Launch of Apollo Flight Hardware”). With the successful conclusion of these test flights, it was time to flight test Apollo program hardware that would actually carry astronauts into Earth orbit.

At this stage of the Apollo program, there were two versions of the Apollo spacecraft being built by North American Aviation (which, after decades of corporate mergers, is now part of Boeing). The first variant, designated Block I, was meant for test flights in low Earth orbit in order to verify the basic Apollo CSM design. Lessons learned from these missions would be incorporated into the improved Block II Apollo CSM which would also include all of the equipment required to support a flight to the Moon. The Apollo CM, which carried the astronauts during their mission and the recovery systems needed to return them safely to Earth, was conical in shape with a diameter of 3.9 meters and a height of 3.2 meters. The SM, which included all the systems and consumables needed to support the astronauts and their mission, was a cylinder with the same diameter. Its appearance was dominated by the 91-kilonewton Aerojet AJ10-137 engine of the Service Propulsion System (SPS) which would be used for all major propulsive maneuvers after the Saturn launch vehicle had finished its task. The total height of the CSM was 11 meters and the Block I version had a nominal mass of up to 20 metric tons or more, depending on its propellant load.

The Apollo spacecraft was topped off by the LES built by the Lockheed Propulsion Company (whose corporate parent is now part of Lockheed Martin). It consisted of a solid rocket motor assembly attached to the top of the CM by means of a truss framework with a total height of 9.9 meters and a mass of 4,200 kilograms. It was designed to pull the CM and its crew to safety in case of an abort situation during the earliest phase of launch and would be jettisoned during the burn of the Saturn second stage when it was no longer needed.

The launch vehicle for the orbital missions of the Block I Apollo was the Saturn IB. This 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 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.

By far the biggest change to create the Saturn IB was to 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 burned by the S-IV. 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, the first flights 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. A tapered adapter consisting of four panels connected the S-IVB stage to the Apollo CSM. During flights of the Saturn V, the LM would also be housed inside this adapter. The Saturn IB, without the payload, was 43.2 meters tall and initially was capable of placing up to 17 metric tons 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.

Preparing for the AS-201 Mission

For the first test flight of the Apollo-Saturn IB, the primary objectives centered on verifying the performance of the Saturn IB as well as checking the structure and some of the vital systems of the Block I Apollo CSM. For this first flight, it was decided that a simple ballistic trajectory with a total flight time of just over half an hour would be sufficient. The Saturn IB designated SA-201 would loft Spacecraft 9, also known as CSM-009, into a suborbital path with a peak altitude of about 425 kilometers. During its arc back towards the Earth’s atmosphere, the SPS of the SM would be fired twice to increase the velocity of the descending spacecraft. The CM would then hit the Earth’s atmosphere at a speed of 8,200 meters per second for a relatively punishing 16 G reentry. This would be slower than a reentry after a return from the Moon but more punishing than a normal reentry from Earth orbit. This would test the Apollo’s heat shield to heating rates as high as 2.3 megawatts per square meter. The CM would then splashdown about 8,500 kilometers downrange where it would be recovered and examined to see how it fared its brief flight.

For the AS-201 mission, the SM carried a light load of only 3 metric tons of propellant for its test of the SPS. The spacecraft would use batteries for electrical power instead of fuel cells which would be needed for longer orbital missions. In addition, CSM-009 would not include an S-band transmission system nor navigation or guidance systems. Instead a fairly simple ad hoc flight-control sequencer would be used. Also missing from CM-009 were astronaut couches, displays and associated equipment. The launch mass of CSM-009 was a relatively light (by Apollo standards) 15,297 kilograms but it was still the heaviest crewed spacecraft design to have been flown into space to date beating the previous record holder, the Soviet Union’s 5,682-kilogram Voskhod 2 launched in March 1965 (see “50 Years Ago Today: The Launch of Voskhod 2“).

The first piece of flight hardware for the AS-201 mission to arrive at Cape Kennedy (which reverted to its original name of Cape Canaveral in 1973) was the S-IB stage on August 14, 1965. Just four days later, it was erected on the pad at Launch Complex 34 (LC-34) along with a dummy of the second stage known as the S-IVB-F which was specifically built for facilities testing. LC-34 had undergone significant upgrades to support Apollo-Saturn IB launches since it was last used for the Saturn I SA-4 test flight in March 1963 and the S-IB-201/S-IVB-F combination was being used for final fit checks of the pad’s new second stage cryogenic propellant loading systems. During subsequent testing of the S-IB stage, the forward bulkhead of one of the fuel tanks was inverted by an accidental overpressurization on September 10. On September 28, the S-IVB-F was destacked and the damaged S-IB fuel tank was replaced the following day. The S-IVB-201 stage for this flight, which had arrived at the Cape on September 19, was stacked on top of the repaired S-IB on October 1. With the addition on October 25 of the IU (Instrument Unit) which controlled the rocket, assembly of Saturn I SA-201 was completed.

As testing on the first Saturn IB proceeded at LC-34, CM-009 arrived as the Cape on October 25, 1965 followed by SM-009 two days later – two years after their construction had started at North American Aviation. Weeks of ground testing of CSM-009 was followed by their erection on top of the waiting Saturn IB the day after Christmas. The addition of the LES on January 24, 1966 finished off the stack. With the successful completion of a flight readiness test on February 19, all was ready for the AS-201 mission.

The Mission

The countdown for the Apollo AS-201 flight officially began at midnight on February 20, 1966. Weather and downrange tracking station issues forced a series of delays over the next few days with the countdown restarting at T-13 hours late on the afternoon of February 25. The countdown got to T-4 seconds when a valve problem in a nitrogen gas tank in the S-IB stage automatically stopped the clock. After an initial decision to scrub the launch, the problem was resolved and AS-201 finally lifted off at 11:12:03 AM EST on February 26. The Saturn IB cleared the tower and 11 seconds into its flight began its pitch maneuver to head downrange towards it target recovery area in the South Atlantic. The only problem encountered during this launch was on the ground. A high voltage fuse in an electrical substation was shaken loose seconds after liftoff which prevented the water quenching system at LC-34 from operating. The undampened flame and vibration from the ascending rocket caused substantial damage to the pad.

The S-IB stage worked almost perfectly with the last of its improved H-1 engines shutting down only a fraction of a second later than planned 147 seconds after launch. At an altitude of 58 kilometers, the untried S-IVB stage separated from the first stage and began its ignition sequence. The J-2 engine came to life for the first time in flight and continued to accelerate its payload downrange. At 173 seconds after launch, the spacecraft’s LES was no longer needed and was jettisoned. This was followed by the ejection of a pair of camera pods from the spent S-IB stage which had recorded the S-IVB separation (only one of which was successfully recovered downrange). The only major anomaly during the burn of the S-IVB stage was a slightly lower thrust of the J-2 engine due to a deviation from the prescribed propellant mixture ratio. The guidance system of the Saturn IB compensated by allowing the J-2 to burn for an extra 9.3 seconds. At engine cut off ten minutes after launch, the AS-201 spacecraft was 740 meters higher and travelling only 0.5 meters per second slower than intended although the spacecraft was now 31 kilometers farther downrange than expected owing to the longer burn of the S-IVB stage.

After coasting for four minutes, the four panels of the adapter connecting the Apollo CSM to its launch vehicle opened up to release the spacecraft. The thrusters on the SM then fired for 18 seconds to pull the Apollo clear of the spent S-IVB. The Apollo continued to follow its ballistic arc over the Atlantic reaching a peak altitude of 418.7 kilometers some 4,473 kilometers downrange at 18 minutes and 4 seconds after launch. The thrusters on the SM fired again 97 seconds later to settle the propellant in its tanks followed 30 seconds later by the ignition of the SPS to increase the speed of the descending CSM back into Earth’s atmosphere. Unfortunately, helium gas inadvertently ingested by the oxidizer tank during ground testing resulted in a decrease in thrust after about 80 seconds with the AJ10-137 engine generating only 30% of its intended thrust by the time of engine cutoff 104 seconds later. The engine continued to experience problems during a second ten-second burn of the SPS shortly afterwards that was meant to test the system’s restart capability. With its job completed, the spacecraft turned 90° and the SM separated from the CM. The CM then used its own attitude control thrusters to continue to turn its heat shield towards the direction of travel in preparation for the final phase of the test flight: reentry and recovery.

With the shortfall in the performance of the SPS, the Apollo AS-201 CM was travelling 238 meter per second slower on a flight path 0.44° shallower than planned during reentry. A fault in the CM’s electrical power system also caused a loss of steering control with the CM left rolling during reentry. While the heat shield temperature reached 2,000° C during reentry, the braking loads only peaked at 14.3 Gs – higher than expected during a normal reentry but still lower than the 16 Gs intended for this test flight. The heat shield of the new CM worked as expected and the descending spacecraft deployed its parachutes as planned. The Apollo CM-009 landed at 11:49:20 AM EST in the Atlantic Ocean 320 kilometers from Ascension Island. The flight had lasted 37 minutes and 20 seconds with the spacecraft travelling 8,472 kilometers downrange missing its intended landing point by 74 kilometers. The CM automatically deployed its recovery aids after splashdown and was picked up 2½ hours later by the Essex-class carrier, the USS Boxer.

Despite the issues uncovered during the flight, almost all of the mission’s objectives were met. The Saturn IB experienced only minor problems during its inaugural flight with good telemetry received. Despite the problems experienced by the Apollo CSM during its flight, all of the mission’s primary test objectives were met even though the heating rate during reentry was lower than expected. The problems with the SPS as well as the other minor issues encountered during the flight did force a postponement of the AS-202 unmanned mission which would send a Block I CSM on a longer suborbital flight in preparation for the first of two planned crewed Block I Apollo orbital test flights. By April 1966, Apollo program officials decided to launch the AS-203 Saturn IB development test flight, which would not fly with an Apollo spacecraft, before AS-202 to limit the impact on program’s tight schedule (see “AS-203: NASA’s Odd Apollo Mission“). With this first success under their belts, NASA was now one step closer to reaching the Moon before the end of the decade.

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Related Video

Here is an excellent NASA film giving a status report on the development of Apollo during late 1965 to early 1966 including the launch of AS-201.

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Apollo Spacecraft Status Report No. 2 1966 NASA; Progress of Apollo CSM & LM Development from Jeff Quitney on Vimeo.

Related Reading

“The First Launch of Apollo Flight Hardware”, Drew Ex Machina, January 20, 2016 [Post]

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

General References

David Baker, The History of Manned Space Flight, Crown Publishers, 1981

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 First Saturn IB Launch Vehicle Test Flight AS-201, MPR-SAT-FE-66-8, May 6, 1966