By the summer of 1966 it had already been five years since the late President John F. Kennedy had committed the United States to a manned lunar landing by the end of the decade. While the US seemed to have had a slow start as the Soviet Union chalked up one important space first after another, by the summer of 1966 the American space program was making visible progress. In the beginning of June, NASA had landed Surveyor 1 on the lunar surface (see “Surveyor 1: NASA’s First Lunar Landing”). Two months later, Lunar Orbiter 1 reached the Moon and started a systematic mapping of potential lunar landing sites (see “Lunar Orbiter 1: America’s First Lunar Satellite”).

In the mean time, the manned Gemini missions were proceeding at an increasing rate helping NASA learn the skills as well as perfect the techniques and test the technologies required to perform the Apollo mission. In July 1966 NASA successfully flew the Gemini 10 mission which included a double rendezvous and a series of EVAs (see “Gemini 10: Dual Rendezvous in Space”). The final two Gemini flights were being prepared to finish the program by the end of 1966. In parallel, flight testing of the highly advanced Apollo spacecraft and their Saturn launch vehicles had already begun. In August 1966 there was one final automated Apollo test flight, designated AS-202, which remained to be flown before NASA would fly its first manned mission scheduled for February 1967 which would become known as “Apollo 1”.

The Hardware

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 (Command-Service Module) design. Lessons learned from constructing and flying these versions would be incorporated into the improved Block II Apollo CSM which would include all of the equipment required to support a flight to the Moon. The Apollo CM (Command Module), 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 (Service Module), 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 in excess of 20 metric tons.

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 Apollo missions in Earth orbit was the Saturn IB. 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 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 at launch 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 used on the S-IV. The S-IVB stage also included a pair of auxiliary propulsion system modules which provided roll control during the burn of the J-2 as well as attitude control while coasting in orbit. This was topped off by the Instrument Unit (IU) which controlled both stages of the launch vehicle. In addition carrying the CSM or LM (Lunar Module) into Earth orbit for initial test flights, the first launches 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 was capable of placing about 21 metric tons into low Earth orbit. The total height of the Apollo-Saturn IB was 68.3 meters and it had a typical lift off mass of 598 metric tons.

Mission Objectives & Plan

The Apollo AS-201 mission launched on February 26, 1966 was the first spaceflight of the Block I CSM and the Saturn IB (see “The First Flight of the Apollo-Saturn IB”). While all the primary mission objectives were met, problems encountered during this 37-minute suborbital test flight, especially during the pair of burns of the SM’s SPS, forced a postponement of the AS-202 mission to resolve the issues. In the mean time, the AS-203 mission was launched out of the originally intended sequence on July 5. The objectives of the AS-203 mission, which was never intended to fly with an Apollo spacecraft, concentrated on testing the Saturn IB especially various design features of the S-IVB stage during orbital flight before the stage was flown on the Saturn V (see “AS-203: NASA’s Odd Apollo Mission”).

For this final unmanned test flight of the Apollo-Saturn IB, the primary objectives centered on a thorough testing of various of spacecraft systems before the first manned flight in early 1967 designated AS-204 or, as it would become better known, Apollo 1. Like AS-201, the AS-202 mission objectives could be met with a suborbital flight. But instead of just a 37-minute mission as AS-201 flew, this would be a longer 93-minute flight which would end with a splashdown almost three quarters of the way around the globe in the Pacific Ocean about 28,700 kilometers downrange.

While the CSM-009 flown on the earlier AS-201 mission did not carry many systems required for a crewed flight, the payload for the AS-202 mission was the fully functional Block I CSM-011 more or less in the configuration intended for the first manned test flight. Notable differences included the omission of the three astronaut couches, some crew equipment and the post-landing cabin ventilation system. In lieu of a crew to control the spacecraft, CM-011 carried an electro-mechanical flight control sequencer to put the various systems through their paces during the flight. Also included were four cameras, three auxiliary batteries and flight-specific instrumentation. Unlike the AS-201 mission which relied on batteries for power, SM-011 carried two operational fuel cells (and one non-operational unit) capable of a maximum electrical power output of 2.84 kilowatts to test this vital hardware in space.

After the mission’s Saturn IB launch vehicle, designated SA-202, had finished its job at an altitude of 217 kilometers some 1,559 kilometers downrange, CSM-011 would separate from the spent S-IVB stage. The S-IVB stage would then conduct a test like that performed during the AS-203 mission where the pressure differential across the common bulkhead between the liquid hydrogen and LOX tanks is increased until the bulkhead fails in order to verify ground test results. Right after separating from the S-IVB, the SM would fire the main engine of the SPS for 215 seconds to boost the spacecraft’s apogee to 1,136 kilometers over South Africa about 41 minutes after launch. Since one of the important test objectives for this flight was to subject the CM’s heat shield to high heat loads, 25 minutes after apogee the SPS would be fired a second time for 88 seconds to increase the descent rate. This would be followed by two more short burns of the SPS in quick succession to test the rapid restart capability of the engine.

After separating from the SM, CM-011 would hit the atmosphere at a speed of 8,500 meters per second at a shallow angle of just -3.48°. After dipping to an altitude of 66.4 kilometers, the spacecraft’s guidance system would use the CM’s lift to steer back up out of the atmosphere to an altitude of 80.6 kilometers before descending to Earth for the final time at 7,150 meters per second. This double skip reentry profile would be used by the Apollo CM during its return from the Moon and this flight would provide actual flight data to verify the CM’s hypersonic aerodynamic properties derived earlier from wind tunnel testing. While this reentry profile subjected the CM heat shield to lower heating rates, it still had to contend with a total heat load of 260 megajoules per square meter. Although this heat load was just a fraction of that the CM would experience during a return from the Moon, it would still certify the CM for return to Earth from orbital flight.

After its double-skip reentry, the CM would splashdown in the north central Pacific Ocean where it would be recovered. If the CM experienced a guidance system failure, it would follow a simpler ballistic reentry like on the AS-201 mission but splashdown 1,600 kilometers uprange. In order to cover this and other contingencies including the uncertainties in the CM’s actual lift-to-drag ratio, the recovery area for the AS-202 mission was 6,500 kilometers long and 370 to 560 kilometer wide cutting between the Caroline and Wake Islands with an impact point centered 550 kilometers southeast of Wake Island. The recovery force would consist of the Essex-class aircraft carrier, the USS Hornet, a pair of destroyers and seven C-130 search aircraft.

The launch mass of CSM-011 for the AS-202 mission was 20,275 kilograms including 10,580 kilograms of SPS propellant as well as 327 kilograms of liquid hydrogen and LOX reactants for the fuel cells in the SM. This was almost five metric tons heavier than CSM-009 flown during the AS-201 mission making CSM-011 the heaviest crewed spacecraft prototype ever to fly into space up until that time. The total launch mass of the fully fueled Saturn IB and its Apollo spacecraft payload for this mission was 595.3 metric tons.

The AS-202 Flight

The first major piece of flight hardware to arrive at Cape Kennedy, Florida was the second stage of the launch vehicle, designated S-IVB-202, on January 31, 1966. This was followed by the first stage, S-IB-2, which arrived by barge a week later. The S-IB was erected on the pad at Launch Complex 34 (LC-34) on March 4 just six days after the launch of AS-201. The S-IVB-202 was added to the stack at LC-34 on March 10 with the addition of the IU the following day completing the rocket. The SA-202 launch vehicle was then put through a series of pre-launch tests over the following month. With LC-34 tied up for several months with preparations for the AS-202 mission, the newly renovated LC-37B was used to support the AS-203 which was being prepared in parallel for its mission.

Meanwhile, the components of CSM-011 arrived at the Cape in April and, after an initial inspection, the SM was taken to LC-16 for checks of its secondary propulsion system. This was followed by fuel cell installation and a series of tests including under vacuum conditions inside an altitude chamber. After the individual spacecraft modules were integrated in June, they were finally erected atop of SA-202 at LC-34 on July 2. Following more checks and the successful completion of a Flight Readiness Review on August 11, the AS-202 mission was ready for its first launch attempt at 12:30 PM EDT on August 25.

The countdown for the first launch attempt of the Apollo AS-202 mission started at 11:30 PM EDT on August 24. Ground computer issues, the threat of Hurricane Faith hitting the downrange tracking station in Antigua all affected the countdown. Finally at 1:15:32 PM EDT (17:15:32 GMT) on August 25, AS-202 lifted off from LC-34 into high broken cloud cover only 45½ minutes behind schedule. The last of the S-IB’s eight H-1 engines shutdown two minutes, 23.47 seconds after launch – this was 1.27 seconds earlier than predicted but the ascending rocket was already travelling 21 meters per second faster than planned.

The trio of ullage motors on the S-IVB stage fired with the stage separation monitored by a pair of movie cameras on the spent S-IB stage. Despite some minor valve malfunctions in the recirculation system of the J-2, the S-IVB’s engine ignited and continued pushing the rocket and its payload on towards space. As the spent S-IB-2 stage continued along a ballistic arc reaching an altitude of 97.2 kilometers and brushing the edge of space, the cameras which recorded stage separation were ejected but only one was located and recovered.

Meanwhile, as the S-IVB-202 stage was near the beginning of its burn, the LES along with the boost protective cover of the CM was jettisoned two minutes and 49 seconds into the flight. Because of some issues controlling the propellant mixture ratio of the J-2 during what was suppose to be a seven minute, 35 second burn, the J-2 shut down almost 14 seconds earlier than planned with the ascending craft travelling only 0.6 meters per second faster and 90 meters lower than planned. At an altitude of 222 kilometers, the CSM separated from the spent S-IVB stage and 11 seconds later fired its SPS for 216.7 seconds.

These events were monitored live by a television camera mounted on the S-IVB transmitting via the Antigua tracking station. The spent S-IVB-202 proceeded to conduct its structural tests reaching a peak altitude of 269 kilometers some 2,858 kilometers down range 13 minutes and 20 seconds after launch. Telemetry finally ceased 141 seconds after apogee when the bulkhead between the S-IVB propellant tanks failed and the descending stage lost structural integrity. The debris burned up during reentry and the Antigua tracking station, with its tasks completed, was finally forced to shut down 45 minutes after launch due to Hurricane Faith.

After the first burn of the SPS, CSM-011 was travelling with a fixed space velocity of 7,772 meters per second at an altitude of 338.4 kilometers. As the Apollo approached apogee, the spacecraft turned its nose towards the Earth as part of a thermal test reaching a peak altitude of 1,143 kilometers at a mission elapsed time of 41 minutes and 14 seconds. The only issues during this time included a weaker than expected signal from the unified S-band communication system resulting in spotty telemetry from this system and when the glycol evaporator of the environmental control system ceased functioning for 54 minutes allowing its outlet temperature to exceed 24° C.

As AS-202 was descending back to Earth over the Indian Ocean, the CSM reoriented itself to align its nose with its velocity vector. Some 24 minutes, 42 seconds after reaching apogee, the SPS ignited for a second time at an altitude of 457.4 kilometers. This 89.2 second burn was followed nine seconds later by two brief 3.8 second burns of the SPS to test the system’s rapid restart capability. The end of the last SPS burn was one hour, 7 minutes and 51 seconds into the mission with CSM-011 at an altitude of 346.0 kilometers travelling at a fixed space speed of 8,449 meters per second. A couple of minutes later, the Apollo modules separated and the CM prepared itself for reentry.

The CM reached its entry interface at an altitude of 122 kilometers travelling at a fixed space velocity of 8,690 meters per second. The guidance system steered the CM through a double skip reentry initially dipping to an altitude of about 64.7 kilometers then rising up to 78.5 kilometers before making its final plunge back into the atmosphere. During the reentry, the heat shield is calculated to have reached a temperature of about 1,500° C while the interior never exceeded 21° C. CM-011 automatically deployed its parachutes and splashed down at 16.11° N, 168.90° E about 805 kilometers southwest of Wake Island at 18:48:34 GMT after a flight lasting one hour, 33 minutes and two seconds. Because the CM’s lift-to-drag ratio was about 15% lower than expected and the entry was 0.05° steeper than planned, the AS-202 CM had come down 380 kilometers short of its aim point.

Once the CM had been spotted by aircraft, rescue swimmers were deployed and attached a flotation collar to help stabilize the capsule. Ten hours after launch, the USS Hornet arrived and recovered CM-011. The Apollo CM was then shipped to North American Aviation’s facility in Downey, California where engineers thoroughly studied the craft and its heatshield. Despite some minor issues, the AS-202 mission had achieved all of its objectives thus human rating the Saturn IB and the Apollo spacecraft for the first Apollo manned test flight scheduled for launch in six months. In the mean time, there was still much work to do but by the end of the summer of 1966, Apollo was getting ready for its next big step in the race to the Moon.

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Related Video

Here is a brief video showing the S-IVB-202 stage separation as viewed from inside the interstage.

This is an excellent 1968 NASA documentary with a detailed tutorial on Apollo’s double skip reentry technique (first demonstrated during the AS-202 mission) entitled “Apollo Atmospheric Entry Phase”.

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Related Reading

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

“AS-203: NASA’s Odd Apollo Mission”, Drew Ex Machina, July 5, 2016 [Post]

General References

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

Ernest Hillje, Entry Flight Aerodynamics From Apollo Mission AS-202, NASA TN D-4185, NASA Manned Space Center, October 1967

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

Pamelia Pack, AS-202 Launch Vehicle Operational Flight Trajectory, NASA TM X-53470, NASA Marshall Space Flight Center, June 3, 1966

“Apollo/Saturn 202”, NASA Press Release 66-213, August 21, 1966