As the year 1967 began, NASA had ambitious plans in place to land astronauts on the Moon before the end of the decade. Unfortunately, the loss of the Apollo 1 crew in a fire on the pad during what should have been a routine countdown dress rehearsal on January 27, 1967 brought manned test flights of Apollo hardware to an abrupt halt (see “The Future That Never Came: The Unflown Mission of Apollo 1”). As investigators looked into the causes of the Apollo 1 tragedy and potential remedies, other aspects of the Apollo program were also experiencing delays making it appear less and less likely that Apollo would land on the Moon within the three years left of the decade.

With this bad start, NASA and a constellation of contractors worked hard to get Apollo back on track. Meanwhile unmanned lunar missions continued to achieve their goals supporting the Apollo program. With the successful conclusion of the Lunar Orbiter 3 mission launched on February 3, 1967 (see “Lunar Orbiter 3: Preparing for Apollo”), NASA had mapped all of the perspective Apollo landing sites leaving the last two Lunar Orbiter missions to pursue other objectives. These included completing the mapping of the Moon and the checkout of other sites of more scientific importance which later Apollo missions might visit. And with the successful completion of the Surveyor 6 lunar landing mission launched on November 7, NASA had shown that all of the proposed mare landing sites would be safe for manned landings freeing up the last Surveyor flight to explore a different site of scientific interest (see “Surveyor 6: The Third Time is the Charm”).

As the end of 1967 approached, NASA was ready to push ahead with a launch schedule which, in many ways, was even more ambitious than their original. Only nine months after the Apollo 1 accident, NASA was preparing the unmanned Apollo 4 mission for the first test flight of the Saturn V rocket which would launch the Apollo spacecraft and crew to the Moon. While earlier test programs of new launch vehicles typically involved a long series of test flights to verify each element of the new design, the Apollo 4 mission would be an “all up” test of the largest rocket ever built by the US with all three stages live – a decision that had been made in November 1963 by NASA’s then-new Director of the Office of Manned Space Flight, George E. Mueller.

The Saturn V

The most visible piece of hardware to be tested on the Apollo 4 mission, which was also known by the designation “AS-501” in planning documents, was the Saturn V launch vehicle. The three-stage Saturn V was the brainchild of the team of engineers led by famed German rocket pioneer, Wernher von Braun, at NASA’s Marshall Space Flight Center (MSFC) in Huntsville, Alabama which had previously developed the Saturn I and upgraded Saturn IB heavy-lift launch vehicles. Based on studies started in May 1961 after President Kennedy had committed the nation to a manned lunar landing by the end of the decade, work on the Saturn V began in earnest by the end of 1962 after months of studying the various option available.

The first stage of the Saturn V was designated the S-IC stage. While Boeing was selected as the prime contractor to construct a pair of non-flight stages and 13 flight models of the S-IC, the initial batch of non-flight and the first two flight models (including the stage to be used for the Apollo 4 mission) were assembled in house by MSFC, much as had been done in the early days with the Saturn I. The S-IC was a cylinder with a diameter of ten meters and a length of 42 meters carrying 1,196 metric tons of RP-1 and liquid oxygen (LOX). Its five F-1 engines built by Rocketdyne (which was then a division of North American Aviation and is today part of Aerojet-Rocketdyne) generated 33,360 kilonewtons of thrust at lift off for this first test flight – almost five times the lift off thrust of the Saturn IB with its eight Rocketdyne H-1 engines. The purpose of the S-IC was to get the huge rocket off of the ground and start it on its way during a nominal 150-second burn that would get the ascending rocket to an altitude of about 62 kilometers and a speed of 2.7 kilometers per second.

The second stage of the Saturn V was designated the S-II stage with North American Aviation as its prime contractor (which merged with Rockwell in March 1967 and subsequently with Boeing 29 years later). Unlike the S-IC and most earlier rockets, the S-II burned the high-energy combination of liquid hydrogen and LOX which yields about half again as much thrust as a like mass of more conventional propellants. With the same ten meter diameter as the S-IC stage, this stage was 24.8 meters long and carried 429 metric tons of cryogenic propellant. Its five Rocketdyne J-2 engines generated a total of about 4,450 kilonewtons of thrust in its initial versions. With a nominal burn time of 367 seconds, the S-II provided most of the energy to drive the rocket and its payload towards Earth orbit during a typical Apollo lunar mission with burnout occurring at an altitude of 188 kilometers and a speed of 6.8 kilometers per second.

The third stage of the Saturn V, with the Douglas Aircraft Company as the prime contractor (which, after decades of mergers, is now also part of Boeing), was designated the S-IVB stage. It had a diameter of 6.6 meters, a length of 17.8 meters and was connected to the S-II stage by a tapered interstage section. It carried 104 metric tons of cryogenic propellants for a single, restartable J-2 engine which would burn briefly during ascent with a thrust of 890 kilonewtons on its initial flight to place itself and its payload into a temporary Earth parking orbit and then later reignite to push on towards the Moon. The S-IVB stage also included a pair of auxiliary propulsion system (APS) modules each with a trio of hypergolic-fueled 670-newton engines which provided roll control during the burn of the J-2 as well as attitude control along all three axes while coasting in orbit. Each APS also included a 310-newton ullage engine to help settle the propellants in their tanks prior to reigniting the J-2 engine.

The Saturn V was topped off by the Instrument Unit (IU), with IBM as the prime contractor, which controlled all three stages of the launch vehicle during all aspects of flight. Based on earlier work for the Saturn I and IB rockets, the IU incorporated the latest innovations in miniaturized electronics. The total height of the Saturn V with its Apollo payload attached was 111 meters and the first flight model with its payload had a liftoff mass of 2,824 metric tons.

Unlike the S-IC and S-II stages which had never flown before, the S-IVB-200 version of the stage and its IU had already been successfully flown three times as the second stage of the Saturn IB with the first flight coming in February 1966 in the AS-201 mission (see “The First Flight of the Saturn IB”). The second flight of the Saturn IB, designated AS-203 launched in July 1966, was flown specifically to test systems related to the similar S-IVB-500 version to be used by the Saturn V (see “AS-203: NASA’s Odd Apollo Mission”). Flown without an Apollo spacecraft and with a smaller load of LOX, the lightened S-IVB stage of the AS-203 mission was orbited with 8.6 metric tons of liquid hydrogen still left in its fuel tank to test various design features to help control the behavior of the fuel under weightless conditions. While the APS of the S-IVB-200 series stages did not include ullage engines to settle the propellant in the tanks like the S-IVB-500, the stage’s venting system was modified to perform the same function well enough to allow the restart procedure for the J-2 engine to be tested in orbit (although an actual restart was not possible or even planned due to inadequate amount of LOX available at this point in the mission).

The Apollo Spacecraft

While testing the Saturn V was the most obvious objective of the Apollo 4 mission, there were also important tests of the Apollo spacecraft itself. Originally, there were actually two versions of the Apollo spacecraft being built by its prime contractor, North American Aviation. The first variant, designated Block I, was essentially a prototype meant for test flights in low Earth orbit for the purpose of verifying the basic Apollo CSM (Command-Service Module) design. Lessons learned from constructing and flying these versions would be then incorporated into the improved Block II 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 as well as 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.

During the initial stages of the ascent, the Apollo spacecraft was topped off by the launch escape system (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 3,720 kilograms. It was designed to pull the CM and its crew to safety in case of an abort situation during the earliest phases of launch and would be jettisoned during the burn of the Saturn V second stage when it was no longer needed. The LES included a lightweight boost protective cover (BPC) made of fiberglass and cork which protected the outer hull and windows of the CM during the early phases of ascent and when the LES was jettisoned.

A tapered Spacecraft Launch Adapter (SLA) consisting of four panels connected the S-IVB stage to the Apollo CSM during the launch phase of the mission. The LM (Lunar Module) would also be housed inside this adapter beneath the SM. Built by Grumman Aircraft, the LM was designed to land a pair of astronauts on the lunar surface and return them back to orbit and the awaiting CSM after a couple of days of exploration. It consisted of a descent stage with its own propulsion system and landing gear to get from lunar orbit to a soft landing and an ascent stage which housed and supported the astronauts along with its own propulsion system to lift off the lunar surface and return to orbit.

The Block I CSM had already been flown twice before. The unmanned Apollo AS-201 mission launched on February 26, 1966 was the first spaceflight of a production model CSM as well as the first flight of its Saturn IB launch vehicle (see “The First Flight of the Apollo-Saturn IB”). While all the primary mission objectives were met by CSM-009 (Command-Service Module number 009), 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 follow on AS-202 mission in order to resolve the issues. The final unmanned Apollo-Saturn IB test flight, AS-202, launched CSM-011 on a 93-minute suborbital test flight on August 25 which ended with a splashdown in the Pacific Ocean. The spacecraft met its mission objectives and the CM successfully executed a double-skip reentry profile certifying the CSM for manned orbital flight (see “AS-202: The Last Test Flight Before Apollo 1”).

The Mission Plan

The laundry list of objectives for the unmanned Apollo 4 test flight can be summarized as basically to test the Saturn V and evaluate the CSM for key aspects of an actual flight to the Moon. The first flight model of the Saturn V, designated SA-501, was fitted with sensors to return 2,894 different measurements of launch vehicle performance via 22 telemetry systems so that all aspects of the flight could be monitored. The Apollo 4 mission was to lift off from Pad A of the new Launch Complex 39 whose facilities had already been checked out during the summer of 1966 using a non-flight model of the Saturn V known as SA-500F (see “The Saturn 500F: The Moon Rocket That Couldn’t Fly”). SA-501 would place its S-IVB stage and a modified Block I Apollo spacecraft into a 188-kilometer orbit where it would remain for two revolutions much as it would during an actual lunar mission. The S-IVB stage would reignite for the first time in flight for a five-minute burn that would place the stage and its payload into a new orbit with an apogee of 17,400 kilometers which would intersect with the Earth’s atmosphere over the Pacific Ocean as it approached perigee.

After the S-IVB had finished its work, the CSM would separate from the spent stage and use the SPS to raise the apogee by another 965 kilometers. After performing a series of system tests during its long climb and return from apogee, the SPS would reignite during the spacecraft’s descent back towards the Earth to boost the reentry speed to 11.1 kilometers per second in order to test the CM heat shield under the same conditions it would experience during an actual return from the Moon. After performing a “double skip” reentry first tested during the unmanned AS-202 test flight, the CM would then splashdown 1,000 kilometers northwest of Hawaii after a flight of 8 hours and 41 minutes where it would be recovered by awaiting US Navy ships.

The Apollo spacecraft for this mission was CSM-017. With a fully fueled launch mass of 30.4 metric tons, this would be the most massive manned spacecraft prototype ever flown. Although it was a Block I type Apollo which would not be employed in subsequent manned flights (a decision which predated the Apollo 1 accident), CSM-017 carried a number of modifications to flight test upgrades for the Block II series spacecraft proposed in the wake of the Apollo 1 accident. These included the umbilical running along the rim of the heat shield from the CM to SM and an outer panel which simulated the new quick-release, outward-opening CM hatch to test its flexible thermal seal in flight. The hatch window was replaced with an instrumented test panel carrying simulations of the seals and gaps between the hatch and the surrounding heat shield. The arrangement of antennas emulated that of the Block II design and the CM used the same type of protective thermal coating that would be employed by the Block II spacecraft.

Since there would be no crew, the interior of CM-017 did not carry astronaut couches as well as some flight controls and instrumentation displays just like the earlier unmanned Apollo test flights. Fitted inside of the cabin was a 163-kilogram electromechanical command controller unit that would execute a preprogrammed sequence of commands or respond to ground commands to put the Apollo spacecraft through its paces during independent flight. This design had been successfully used in the earlier AS-202 unmanned test flight. A Maurer Model 220-G 70 mm camera with a 42° field of view was also fitted to one of the CM cabin windows to take photographs of the Earth at 10.6-second intervals for a two-hour period centered on apogee.

Since the objectives of the Apollo 4 mission did not include the LM, a boilerplate model designated LTA-10R (Lunar Test Article-10R) was carried instead by SA-501 to simulate the mass and dynamic properties of this part of the payload. With a mass of 13.4 metric tons, LTA-10R consisted of a flight-type LM descent stage without landing gear topped by a ballasted aluminum structure to simulate the ascent stage. Originally built as LTA-10 by Grumman for use in fit checks and separation tests by North American for its SLA work, it was refurbished to become LTA-10R for use as a flightworthy stand-in for the LM in the Apollo 4 mission. The propellant tanks of the mock descent stage were filled with a water-glycol mixture and Freon to simulate the characteristics of fuel and oxidizer for the LM propulsion system. Instrumentation mounted on 36 points on LTA-10R would return data on the dynamics of the structure during the first 12 minutes of flight. No flight instrumentation was included in the simulated ascent stage structure. LTA-10R would remain attached to the spent S-IVB stage after separation of the CSM and be destroyed along with the spent stage during reentry over the Pacific.

Preparing the Giant for Flight

Construction of the individual three stages of SA-501 had begun by late 1964 after the manufacturing techniques and equipment had been tested on earlier non-flight test hardware – months before NASA had even launched their first crewed Gemini mission (see “50 Years Ago Today: The Launch of Gemini 3”). The third stage, designated S-IVB-501, was the first major piece of mission hardware to arrive at Cape Kennedy (which reverted to its original name, Cape Canaveral, in 1973) on August 15, 1966 and was moved to the new Vehicle Assembly Building (VAB) at Launch Complex 39 to begin preparation for stacking. The IU arrived ten days later followed by the components of the SLA on September 9.

Next, the S-IC-1 first stage arrived by barge at the Cape on September 12, 1966 after which it was immediately moved to the transfer aisle inside the VAB. The original intent was to stack all three stages of AS-501 to begin a series of integrated systems tests but delivery of the S-II-1 second stage from North American was running months behind schedule as they wrestled to resolve a list of issues during its manufacture and testing. In order to keep SA-501 processing on schedule, it had already been decided that the initial stacking of AS-501 would instead use a substitute – a S-II simulator designated H7-17 which had been originally constructed for handling training and test facility fit checks. The H7-17 test article basically consisted of a small diameter, load-bearing center column with S-II interfaces at either end giving the article a distinct spool-like shape. The S-II simulator arrived at the Cape on August 16 and was immediately moved to the VAB where it was modified to serve in its new role as a temporary spacer.

Initial stacking of SA-501 in the VAB began on October 27, 1966 when S-IC-1 was placed on MLP-1 (Mobile Launch Platform 1) only days after the destacking of the non-flight test vehicle, SA-500F, had been completed. The S-II-spacer was added to the stack on October 31 followed by S-IVB-501 and IU-501 on the subsequent two days. The S-IC stage was powered up on November 7 for the beginning of three months of checks on the launch vehicle.

The SM of CSM-017 arrived at Cape Kennedy on December 21, 1966 with the CM joining on Christmas Eve day. After checkout, the spacecraft was erected on January 12, 1967 for preliminary testing with its launch vehicle 11 days later. After SA-501 had finished its first overall test on January 24, the process of destacking began on February 13. CSM-017 was moved back to the Manned Spacecraft Operations Building for reinspection and modifications resulting from the problems uncovered during the Apollo 1 investigation. Modifications were also made to S-IVB-501 and S-II-1 was finally available having arrived at the Cape via barge on January 21. The newly arrived S-II stage was stacked on February 23 followed the next day by the restacking of the S-IVB stage and IU to begin another round of checks and testing of the huge Saturn V rocket. The S-II-spacer was returned to the Mississippi Test Facility (today known as NASA’s Stennis Space Center) to perform fit checks at a new test stand there only to be returned to the Cape on March 10 to be used once again as a spacer in the initial stacking of SA-502 (whose S-II-2 stage was also late) which would fly the second unmanned Saturn V test flight, Apollo 6.

By March 1967 a total of 1,200 problems resulting in 32 discrepancy reports had to be addressed to get the mission off the ground. But as work on SA-501 and CSM-017 continued, a new problem arose. During the course of constructing S-II-6, engineers at North American (which had just become Rockwell North American in March as a result of a merger) had discovered 80 welding flaws and subsequent investigation suggested that similar flaws existed in S-II-1 as well. The unplanned destacking began on May 27 to commence testing of the suspect stage as well as the S-IC-1 stage which was feared to have similar problems. With no weld problems found, restacking started on June 18 and was completed two days later with the addition of CSM-017 attached to the SLA with the simulated LM payload, LTA-10R, tucked inside.

After two more months of extensive testing, the first flightworthy Apollo-Saturn V was rolled out of the VAB on August 26, 1967 to make the 5.6 kilometer trek to Pad A. After MLP-1 and its rocket reached the pad, they were interfaced with ground support equipment there to begin the long task of checking out the first Apollo-Saturn V for launch. On September 27, RP-1 loading began as part of countdown demonstration test (CDDT). The terminal countdown portion of the CDDT began two days later but continued until October 14 as a result of numerous problems encountered. Among these was a malfunction in the power-producing fuel cells in CSM-017 which necessitated a replacement of this vital system which was completed on October 19. After more hardware repairs and a successful flight readiness test on October 26, all seemed ready for a launch at 7:00 AM EST on November 7.

Getting Apollo 4 off the Ground

But with five days still to go before the scheduled launch of Apollo 4, dealing with a list of minor problems put the pre-countdown work plan 40 hours behind schedule as they were resolved one by one. Reluctantly, the scheduled liftoff was pushed back two days with the launch vehicle “pre-count” activities started at the T-104 hour mark at local noon on November 4, 1967. The precount proceeded smoothly through the following day with only minor problems encounter so that the “terminal count” could start at 10:30 PM EST on November 6 with the clock at T-49 hours. At this point, two more planned holds were in the schedule to help deal with any unexpected issues that might come up: a six-hour hold at T-6.5 hours and a 90-minute hold at T-4 hours.

Again, the countdown proceeded smoothly until 12:31 PM EST on November 8 when an unscheduled hold was called at T-11 hours after a number of minor problems came up requiring time to resolve. This consumed almost two hour out of the originally planned six-hour hold. A second unplanned two-hour hold was called at 5:00 PM at the T-8.5 hours mark to verify that the rocket’s range safety receivers were operating correctly. By the end of the second scheduled hold at 3:00 AM on November 9, the clock picked up at the T-4 hour mark.

Without any additional major problems encountered, the countdown proceeded as planned until launch at 7:00:01 EST (12:00:01 GMT) on November 9, 1967. With the world press watching, the mighty Saturn V SA-501 lifted off from LC-39A and into a mostly sunny Florida sky. After clearing the tower, Apollo 4 started it roll program to align itself for the pitch maneuver downrange over the Atlantic and towards orbit. The spectacular launch shook the Earth and showered broadcasters like CBS anchor Walter Cronkite with debris from their observation stand five kilometers from LC-39A. Later inspection of the pad showed less damage overall than expected but the engine service platform was severely damaged while the launch umbilical tower-level platform was completely destroyed from the blast of five powerful F-1 engines.

Meanwhile, Apollo 4 continued on its historic ascent towards orbit. The center F-1 engine of the S-IC was shutdown by a timer as expected 135.5 seconds after launch to lessen the acceleration loads of the rocket as it consumed hundreds of tons of propellant. The four remaining outboard F-1 engines shutdown as the stage’s LOX supply was depleted at an altitude of 63.7 kilometers some 150.9 seconds after launch – just 1.1 seconds earlier than planned but still well within expectations. After a nearly perfect performance, the S-IC stage was cut loose as the five J-2 engines of the S-II stage began their startup sequence. The interstage was successfully jettisoned with all events captured by a pair of camera pods which were later ejected for recovery downrange.

With all engines on the S-II stage powered up, Apollo 4 continued to accelerate towards orbit. At 187.1 seconds after launch, Apollo’s LES was pulled clear of the ascending craft as it was no longer needed to support abort options for the rest of the mission. The engines of the S-II stage shutdown 3.5 seconds later than planned 519.8 seconds after launch at a slightly higher than expected altitude of 192.3 kilometers. The S-IVB stage cleanly separated from the spent second stage to start the first burn of its J-2 engine for the final push into Earth parking orbit.

The first burn of the S-IVB stage ended 11 minutes, 5.6 seconds after launch with the stage and its Apollo spacecraft payload now in a 183.6 by 187.2 kilometer orbit with an inclination of 32.6°. The total burn time of the three stage of the Saturn V was 9.6 seconds longer than expected but the IU’s guidance system had ensured that the velocity was only 1.2 meters per second lower than planned but about 44 kilometers further downrange – all well within expected performance margins. The Apollo 4 mission was off to an excellent start.

The Apollo 4 Mission

Once in orbit, commands were sent from the Bermuda tracking station to deactivate the destruct package which would have been used in case of trouble during ascent. The IU commanded the APS to keep the S-IVB-501 and CSM-017 combination oriented with its long axis aligned to the orbital plane and level with the local horizontal. The S-IVB stage started continuous venting during its coast to provide sufficient ullage to keep its propellants settled in their tanks. All systems in the combined spacecraft continued to function perfectly during the two revolutions in the low Earth parking orbit much as they would need to do during an actual Apollo lunar mission.

At 15:06:00 GMT some three hours and six minutes after launch, the S-IVB ceased its continuous venting in preparation for its second burn which would simulate the translunar injection burn (TLI) that would send a Moon-bound Apollo mission on its way. At 15:11:27 GMT, the J-2 engine on the S-IVB stage successfully reignited for its second burn. The J-2 engine shutdown after 299.7 seconds leaving the stage and its payload in an orbit with an apogee of 17,209 kilometers but with an atmosphere intersecting perigee 81 kilometers below sea level. This orbit not only meant that the S-IVB would burn up in the atmosphere after less than a full orbit but also ensured that CM-017 would reenter the Earth’s atmosphere even if the SM’s SPS failed during the next phase of the mission.

Ten minutes after the end of the second burn of the S-IVB stage, CSM-017 successfully separated from the spent stage to begin testing of the Apollo spacecraft. The S-IVB-501 stage, now with the COSPAR designation of 1967-113B, continued in its new orbit hitting an apogee of 16,746 kilometers before arcing back and reentering the atmosphere at 23.4° N, 161.4° W over the Pacific at 20:03 GMT. About 98 seconds after CSM-017 had separated from the S-IVB stage, the SPS ignited for its first planned burn at 15:28:07 GMT. The 16-second burn changed the velocity of the Apollo spacecraft by 64.8 meters per second raising the apogee to 18,092 kilometers compared to the planned 18,316 kilometers. As the spacecraft ascended towards apogee, CSM-017 oriented itself so that the simulated quick-opening crew hatched faced the Sun with the sloped surface of the CM perpendicular to its rays. This cold soak produced a thermal gradient across the exterior heat shield of the CM to test it under these stressing conditions. During the 4½ hours in this attitude, the exterior temperature of the CM hull ranged from +60° C on the Sun-facing side to -73° C on the dark side. There were some indications of degradation in the exterior thermal coating likely the result of contamination from the jettisoning of the LES.

At 17:46:50 GMT, CSM-017 reached apogee 5 hours, 46 minutes and 49.5 seconds after launch. During this time, the on board camera secured 715 good quality images of the Earth below. Meanwhile the cabin temperature stayed at a near constant 16° C with the pressure in the 386 to 400 millibar range indicating that leakage rate was negligible and well within specifications. As the unmanned Apollo was descending back towards the Earth, it was reoriented to point its nose roughly towards its velocity vector as it approached reentry. At 20:10:55 GMT, the SPS ignited for a second time to increase the spacecraft velocity to simulate a return from the Moon. The 280.6 second burn was slightly longer than expected and was terminated by ground command after the velocity of CSM-017 had been increased by 1,470 meters per second. The inertial velocity was about 91 meters per second faster than desired but still well within mission specifications.

About 147 seconds after the completion of the second SPS burn, the CM and SM separated and the CM used its own attitude control thrusters to orient itself properly for its impending double-skip reentry. Entry interface at an altitude of 121.9 kilometers was reached at 20:19:29 GMT with the CM travelling at 11,168 meters per second at an angle of -6.93° to the local horizontal. This was 64 meters per second faster and 0.20° shallower than planned due to the longer than expected second burn of the SPS. As a result, the peak braking loads during the CM’s initial dip into the atmosphere reached only 7.27 g instead of the planned 8.3 g but it increased the total reentry heat load to 10.9 gigajoules per square meter instead of 10.3 (compared to 8.4 gigajoules per square meter expected for a normal return from the Moon).

After dipping to within about 56 kilometers of the Earth’s surface, the guidance system used the CM’s lift to skip back out of the atmosphere briefly to reach a peak altitude of 73 kilometers before descending back into the atmosphere for the final time. During this part of reentry, braking loads hit a peak of 4.0 g instead of the predicted 4.3 g primarily due to the longer SPS burn. During the entire reentry, the heat shield and the environmental control system kept the cabin temperature to no higher than 21° C.

With the worst of the reentry completed, CM-017 deployed its drogue chutes at 20:31:19 GMT to stabilize the descending craft followed 47 seconds later by the deployment of the three main parachutes. Splashdown occurred at 20:37:10 GMT at 30.10° N, 172.52° W only 19 kilometers from its target point and about 13 kilometers from the prime recovery ship, the Essex-class carrier, the USS Bennington. The total flight time for the Apollo 4 mission was 8 hours, 27 minutes and 9.2 seconds. Within 20 minutes of splashdown, swimmers dropped by helicopter had attached a floatation collar to the CM as it bobbed in 2½ meter swells. CM-017 was hoisted aboard the USS Bennington with the CM’s apex cover and one of its three parachutes also fished out of the Pacific after a total recovery operation lasting about two hours. The CM was then shipped to Hawaii where its systems were finally shutdown and then sent to Rockwell North American’s facility in Downey California where it arrived on November 15 for a detailed postflight inspection and tests.

The Apollo 4 mission was a complete success with nearly all of its objectives having been met. The gamble associated with the decision made four years earlier for an “all up” test had paid off handsomely. With the possibility that the third planned unmanned Saturn V test flight could be cancelled being seriously considered, it was beginning to appear that the goal of reaching the Moon before the end of the decade could actually be achieved after all. Following the doubts raised in the wake of the fatal Apollo 1 accident, the year 1967 was ending on a positive note as the Apollo program geared up for the final push for the Moon.

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Related Video

Here is an excellent NASA documentary on the Apollo 4 mission.

Related Reading

“The Saturn 500F: The Moon Rocket That Couldn’t Fly”, Drew Ex Machina, September 23, 2016 [Post]

“The Future That Never Came: The Unflown Mission of Apollo 1”, Drew Ex Machina, January 27, 2017 [Post]

General References

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

Ernest R. Hillje, Entry Aerodynamics at Lunar Return Conditions Obtained from the Flight of Apollo 4 (AS-501, NASA TN D-5399, MSC-NASA, October 1969

Gene F. Holloway, Apollo Experience Report – Guidance and Control Systems: Mission Control Programmer for Unmanned Missions AS-202, Apollo 4, and Apollo 6, NASA TN D-7992, JSC-NASA, July 1975

Alan Lawrie with Robert Goodwin, Saturn V – The Complete Manufacturing and Test Records, Apogee Books, 2005

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

First Saturn V Flight Test, NASA Press Release 67-275, November 2, 1967

Apollo 4 Spacecraft Performance, NASA Press Release 67-294, December 3, 1967

Saturn V Launch Vehicle Flight Evaluation Report – AS-501 Apollo 4 Mission, MPR-SAT-FE-68-1,MSFC-NASA, January 15, 1968