When space enthusiasts think about the Apollo program, they instantly recall the lunar missions which landed a total of a dozen NASA astronauts on the Moon. True fans of the Apollo missions will also readily remember the series of crewed test flights flown in Earth and lunar orbit during the nine months leading up to the historic Apollo 11 mission. Less well known, however, are the unmanned test flights which preceded these missions including the often forgotten Apollo 5 mission – the first unmanned test flight of the Lunar Module (LM) which would make the actual landing on the Moon possible.

The First Apollo Test Flights

The Apollo lunar missions actually involved two separate spacecraft: the Command-Service Module (CSM) to support the crew during all phases of the mission save for the actual lunar landing itself which would be left to the purpose-built Lunar Module (LM) with Grumman Aircraft as the prime contractor (which is now part of Northrop Grumman after a 1994 merger). Built by North American Aviation (which merged with Rockwell in March 1967 and subsequently with Boeing 29 years later), initial flights of the CSM used an early Block I variant which was essentially a prototype meant for test flights in low Earth orbit for the purpose of verifying the basic CSM 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 systems needed to support a lunar landing mission.

While the actual flight to the Moon would require the use of the three-stage Saturn V, the early test flights of Apollo hardware in low Earth orbit employed the smaller two-stage Saturn IB – a significantly uprated version of the original Saturn I. Developed by the same team led by Wernher von Braun who was developing the Saturn V at NASA’s Marshall Space Flight Center, the first stage of the Saturn IB, designated the S-IB, was an upgraded version of the S-I stage successfully flown ten times between 1961 and 1965 on the Saturn I (see “The Last Launch of the Saturn I”). The second stage, the S-IVB, was a new and enlarged design which used the same high performance cryogenic propellants as its smaller predecessor, the S-IV. A slightly altered version of the S-IVB-200 series stage used on the Saturn IB, known as the S-IVB-500, would be employed as the third stage of the Saturn V. Early flights of the Saturn IB would thus provided flight experience with this important piece of NASA’s Moon rocket. With an initial payload capability of at least 18 metric tons, the Saturn IB had sufficient performance to launch either a CSM or a LM into Earth orbit for initial Apollo test flights.

The unmanned Apollo AS-201 mission launched on February 26, 1966 was the first spaceflight of a production model Block I 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 #009), problems encountered during this 37-minute suborbital test flight, especially during the pair of burns of the SM’s main Service Propulsion System, forced a postponement of the follow on AS-202 mission in order to resolve the issues.

In the mean time, the AS-203 mission was launched out of the originally intended sequence on July 5, 1966. The objectives of the AS-203 mission, which did not fly with an Apollo spacecraft, concentrated on testing various design features of the S-IVB stage during orbital flight before it was flown on the Saturn V (see “AS-203: NASA’s Odd Apollo Mission”). The next 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”).

By late 1966, NASA’s plans for the next round of Apollo test flights had been set. First up would be the AS-204 mission which would make the first orbital test flight of the Block I CSM with a crew of three on board. The feat would be repeated with a second Block I CSM orbital test flight designated AS-205. Next up would be AS-206 which would be the first unmanned test flight of the LM. Since the Saturn V would not be making its first of two planned test flights until sometime during the second half of 1967 (see “Apollo 4: The First Flight of the Saturn V”), the first crewed test flight of the LM would require a pair of Saturn IB launches as part of a mission designated AS-207/208. Saturn IB SA-207 would launch the first crewed flight of the upgraded Block II CSM followed by an unmanned launch of the first crew-rated LM on SA-208. The two spacecraft would then rendezvous and dock to begin manned testing of the LM.

But as delays in the delivery of key pieces of Apollo hardware caused NASA’s ambitious schedule to slip more and more, in November 1966 program planners modified their test flight schedule. AS-204 would be launched on an open ended mission to be known as “Apollo 1” on February 21, 1967 (see “The Future That Never Came: The Unflown Mission of Apollo 1”). This flight would use Saturn IB SA-204 to launch CSM-012 with its crew of three into Earth orbit. It was decided to eliminate the second crewed Block I CSM flight since it was now considered to be redundant. Next up in April would be the first unmanned test flight of the LM for the AS-206 mission. In August, the dual-launch AS-207/208 mission (now redesignated AS-205/208) would take place with the crew being launched in the first Block II CSM.

The LM Test Flight

The Apollo LM was designed to land a pair of astronauts on the lunar surface and return them back to orbit and the waiting CSM after a couple of days of exploration. The LM was a true spacecraft in the sense that it was designed to operate only in the vacuum of space resulting in a lightweight design with a distinctive angular shape incapable of surviving atmospheric flight. The LM consisted of two stages: the descent stage and the ascent stage. As the name implies, the descent stage was used to make the descent from lunar orbit to the surface. It included landing gear to support the LM on the lunar surface, a supply of consumables for the crew and the LM Descent Engine (LMDE) along with its supply of hypergolic propellant. Built by TRW, the LMDE was a throttleable, pressure fed engine which burned Aerozine 50 (a 50-50 mix of hydrazine and unsymmetrical dimethyl hydrazine or UDMH) and nitrogen tetroxide to generate up to 46 kilonewtons of thrust.

The LM ascent stage housed and supported the astronauts inside of a pressurized cabin with a habitable volume of about 4.5 cubic meters. In addition to life support equipment and supplies for the crew, the ascent stage included a pressure fed LM Ascent engine (LMAE) as well as tanks to hold its Aerozine 50 and nitrogen tetroxide propellants. Jointly developed and built by Bell Aerospace and Rocketdyne, the LMAE produced 16 kilonewtons of thrust to lift the LM ascent stage off of the lunar surface (with the descent stage now acting as a launch platform) and return the LM crew to lunar orbit where it would rendezvous and dock with the CSM for the return home. The LM ascent stage also included a reaction control system (RCS) to provide attitude control for the LM during flight and allow it to perform maneuvers required during rendezvous and docking operations. The RCS consisted of 16 440-newton engines divided into four quads evenly spaced around the midsection of the stage. The LM stood about seven meters tall with its landing gear extended and would have a fully loaded mass of about 15 metric tons in its initial lunar landing flights.

In addition to certifying the general flightworthiness of the LM, the primary objectives of the unmanned Apollo AS-206 mission centered on providing flight verification of the propulsion systems of both LM stages. Also to be tested would be the abort staging function which would be required if a problem were encountered during the LM’s descent to the lunar surface forcing an early return to orbit. During such an abort, the ascent stage’s engine would be ignited while still attached to the descent stage – a technique referred to as “fire in the hole”. Without any attitude control, it was feared that the descent stage might tumble wildly after separation posing a potential hazard for the departing ascent stage. An inflight test of abort staging was essential to verify predictions of the stage’s dynamics during an abort before a crew could be committed to testing the LM in flight. Since the LM had no provisions for landing on Earth, no recovery of the LM was possible at the end of the mission.

The spacecraft for the AS-206 mission was Grumman’s first LM flight article designated LM-1. Because of the nature of its mission, LM-1 differed considerably from subsequent manned versions of this spacecraft. Most notable was the lack of landing gear which was not needed for this flight. In addition to the inclusion of development flight instrumentation and a C-band transponder, LM-1 also included a mission programmer to operate the LM in conjunction with its guidance computer either through a preprogrammed sequence of tasks or by direct ground control. Since this was an unmanned test flight, many crew-related items were excluded from LM-1 including certain flight displays, parts of the environmental control system and other crew provisions. Because of problems encountered during testing, the windows on the LM-1 were replaced with aluminum panels. Other subsystems not required to meet AS-206 mission objectives such as the landing and rendezvous radar systems were also excluded. In its final form, LM-1 had a launch mass of 14,300 kilograms – just a touch lighter than the manned LM on an actual lunar landing mission but still the most massive payload placed into orbit to date.

During a typical Apollo lunar mission, the CSM was connected to the S-IVB stage of the Saturn V by a tapered Spacecraft Launch Adapter (SLA) consisting of four panels. Tucked inside the SLA was the LM protected from aerodynamic forces during ascent. Once on its way to the Moon, the four panels of the SLA would open up freeing the CSM to turn around, dock with the LM and then extract it from the spent S-IVB stage. For the CSM test flights in Earth orbit, the SLA was also employed to mate the CSM to the S-IVB stage of the Saturn IB but the SLA itself was empty. For the AS-206 mission, the CSM and the launch escape system (LES) were omitted this time but the SLA now housed LM-1. In place of the CSM, the SLA would be topped off by a 3.4 meter tall nose cone to give a total launch vehicle height of 55.1 meters.

The launch vehicle for the AS-206 mission, designated SA-206, was the first to sport a number of improvements to the Saturn IB design based on earlier experience. The most visible of these was the change from propellant tanks with alternating black and white colors on the S-IB first stage to solid white in order to address deformation caused by solar heating while on the pad. The S-IB-6 stage also sported eight uprated H-1 engines which boosted the total thrust at liftoff by 2.5% to 7,285 kilonewtons.

A Change of Plans

The S-IVB-206 second stage of SA-206 was the first piece of mission hardware to arrive at Cape Kennedy (which reverted to its original name of Cape Canaveral in 1973) on December 14, 1966 with S-IB-6 first stage arriving by barge four days later. With the November 1966 delivery date of LM-1 already missed and Grumman continuing to struggle with a range of issues during its final assembly and testing, Apollo program planners decided to start preparations for the AS-206 mission with the hope of launching it as soon as possible after the long-delayed Apollo 1 mission. With Apollo 1 and its SA-204 rocket occupying the pad at Launch Complex 34 (LC-34), S-IB-6 was erected on Pad B of Launch Complex 37 (LC-37B) on January 22, 1967. The S-IVB-206 stage was added to the stack on January 23 for the beginning of prelaunch testing.

But as preparations for the launch of AS-206 were starting in earnest at LC-37B, the Apollo program encountered its biggest setback. On January 27, 1967 astronauts Gus Grissom, Ed White and Roger Chaffee died in a fire which swept through their capsule during what should have been a routine countdown rehearsal for the upcoming Apollo 1 mission. As the space agency and the country tried to come to grips with the tragic loss of the Apollo 1 crew, Apollo’s aggressive test flight schedule was placed on hold as the cause of the fire was investigated.

With the continuing delays in the delivery of LM-1, Apollo program officials decided on March 20, 1967 to switch launch vehicles for the LM test flight. SA-204, which was undamaged by the Apollo 1 accident, would now be used. SA-206 was subsequently removed from LC-37B and placed into storage for future use (see “SA-206: The Odyssey of a Saturn IB“). Destacking of SA-204 at LC-34 was completed on April 6 along with a meticulous inspection of the rocket’s hardware. Having been on the pad since the end of August 1966, it was feared that seven months of exposure to the Florida weather might have resulted in corrosion or other problems. The requalified rocket, now officially designated SA-204R, got a clean bill of health and was transferred to LC-37. S-IB-4 was erected on the pad at LC-37B on April 7 followed three days later by S-IVB-204. With the delivery of LM-1 continuing to slip, Grumman built a plywood mockup of the LM as a temporary stand in so that facilities verification could continue.

In the wake of the investigation of the Apollo 1 accident, a number of changes were recommended for the LM design including to its wiring, environmental control system and materials used in the cabin which might present a fire hazard. While many modifications were made, some would require delaying the LM test flight even further. Compromises were eventually made such as certifying the wiring in LM-1 and LM-2 (which would now serve as a backup if LM-1 failed in its mission) for an unmanned flight while saving the more extensive changes to wiring and other systems for subsequent LMs which were not as far along in the construction and testing cycle. The long-delayed LM-1 finally arrived at the Cape on June 23, 1967 and its stages were mated four days later.

During its initial post-delivery inspection, it was found that LM-1 needed considerable work. The LM stages were demated in August to repair of a leak detected in the ascent stage’s propulsion system. After the stages had been mated for a second time, yet another leak was found in September forcing the stages to be separated so that key components could be removed and returned to Grumman for work. After the stages were remated in October and completed more testing, LM-1 was mounted in SLA-7 and moved to LC-37B. The LM enclosed in the SLA was finally mechanically mated to its launch vehicle on November 19, 1967 for the beginning of combined launch readiness testing which ran through December. By year’s end, the launch of the LM test flight, now designated “Apollo 5”, was set to take place on January 18, 1968.

The Apollo 5 Mission

Because of further delays in preparing Apollo 5 for launch, LM-1 cabin closeout did not finally occur until 3:50 PM EST on January 18, 1968 during the countdown demonstration test which was concluded the following day. The terminal countdown for Apollo 5 began at the T-10 hour, 30 minute mark on January 21. A number of holds, planned and otherwise, were called through the countdown to attend to various problem including a failed telemetry computer at the T-3 hour, 30 minute mark. Even though it was considered a mandatory item for this test flight, it was decided that the command computer would provide sufficient coverage of those functions so the countdown could continue. After hours of delays, the 583.6 metric ton SA-204R rocket and its LM-1 payload successfully lifted off from LC-37B at 5:48:08 PM EST (22:48:08 GMT) on January 22 just before local sunset. This would prove to be the last launch from LC-37B for almost 35 years (see “From Apollo to Orion: Space Launch Complex 37”).

A nearly perfect performance by the Saturn IB placed the S-IVB-204 stage and its LM-1 payload into an initial 163 by 222 kilometer orbit with an inclination of 31.6° following 10 minutes and 3.3 seconds of powered flight. After 35 seconds in orbit, the nose cone was successfully jettisoned with the four panels of the SLA deployed 9 minutes and 15 seconds later. LM-1 used its RCS to separate from S-IVB-204 at 23:38:58 GMT about halfway through its first revolution and into a 167 by 224 kilometer orbit. After separation, LM-1 changed its attitude to cold soak its propulsion system for the next two orbits.

With its primary duties concluded, S-IVB-204 performed a number of engineering tests including the dumping of residual cryogenic propellants and helium pressurant through the stage’s J-2 engine. This procedure would help lighten the stage for easier control in orbit and prepare future S-IVB stages for use as a “wet” orbital workshop as proposed for the Apollo Application Program which was planned to follow the initial Apollo lunar landing missions (a program which later evolved into Skylab). After the propellant dump was successfully completed at 01:19:33 GMT on January 23, the stage was in a 155 by 223 kilometer orbit. Although it was not tracked, the orbit of S-IVB-204 was expected to decay ten revolutions after the separation of LM-1 about 15½ hours after launch.

Following the three-hour cold soak of LM-1, a pair of burns were planned for the descent propulsion system (DPS) followed by two burns of the ascent propulsion system (ASE). The first 39-second burn of the DPS would start at a throttle setting of 10% then ramp up to full thrust for the last 12 seconds to simulate the initial deorbit burn which would start the descent towards the lunar surface. The second firing of the DPS would last for 739 seconds and use a series of throttle settings representative of an actual descent to the lunar surface. Immediately afterwards, the abort staging would be tested with an initial five-second burn of the APS. A subsequent firing of the APS would continue until the stage’s propellants were depleted after about 445 seconds completing the primary mission about 6½ hours after launch. Because the LM ascent stage was expected to be left in a comparatively long-lived 315 by 815 kilometer orbit after the completion of the last APS burn, extended mission activities were planned until the ascent stage depleted its consumables about seven hours later.

At 02:47:49 GMT on January 23 (just shy of four hours after liftoff), LM-1 was commanded to start the first of two planned burns of the DPS but the engine unexpectedly shutdown after firing for only four seconds leaving the spacecraft in a 170 by 222 kilometer orbit instead of the planned 215 by 330 kilometer orbit. After examining the telemetry, ground controllers quickly located the source of the problem. The LM’s guidance computer had been programmed to abort the maneuver and shutdown the DPS if it did not provide the expected acceleration level after four seconds – a situation which would normally indicate a problem with the DPS. Because the pressure-fed propulsion system was purposely running at lower than nominal pressure for these tests, it would now take six seconds to reach full thrust. It was this oversight which resulted in the premature shutdown of the DPS.

As a result of the problem, a preplanned alternate mission was adopted by ground controllers which would meet the minimum mission requirements while keeping LM-1 in touch with tracking stations for key maneuvers. With the guidance system deactivated, the DPS was ignited by ground command for a 33-second burn at 04:58:49 GMT during the fourth revolution. The second burn of the DPS for the alternate mission sequence was commanded at 04:59:54 GMT for an abbreviated 28-second burn. This was followed by the abort staging test and a 60-second burn of the APS. All systems worked as intended during this alternate mission’s three burns. The 228 meter per second total change in velocity from these three propulsive maneuvers boosted LM-1 into a 172 by 961 kilometer orbit.

After these first three firings of the propulsion systems, the primary control system was reactivated for the balance of the mission. Unfortunately the guidance computer, which had been in a passive mode during the abort staging, had not taken into account the change in spacecraft mass and used excessively long burns of the RCS to control attitude as if it had a fully loaded descent stage still attached. This resulted in higher than expected RCS usage and eventual propellant depletion after only about an hour. Fortunately the RCS could be configured to draw from the APS propellant supply to provide attitude control during the mission’s final burn. Because of the timing and other requirements of the burns in the alternate mission plan, this second burn of the APS would be in the retrograde direction which would send the spacecraft into Earth’s atmosphere ending the Apollo 5 mission.

With the ground track of LM-1 beginning to drift beyond the mission’s tracking stations due to the one-orbit delay to implement the alternate mission, the remainder of the mission had to be completed by the next revolution. The second burn of the APS started at 06:32:20 GMT during the fifth revolution. As planned, the sequencer automatically closed the valves supplying the RCS with propellant about 161 seconds later. Without attitude control, the ascent stage began to tumble as the APS continued to fire for another 190 seconds before its propellants were finally depleted. The last telemetry was received from LM-1 at 06:40:18 GMT on January 23 ending the Apollo 5 mission 7 hours, 52 minutes and 10 seconds after launch. The LM-1 ascent stage reentered the Earth’s atmosphere and was destroyed over the Pacific Ocean some 640 kilometers off the coast of Central America. The inactive descent stage of LM-1 fell from orbit on February 12.

Although the Apollo 5 mission had encountered problems forcing a switch to an alternate mission plan, the overall performance of LM-1 was good enough to satisfy the mission’s main objectives. And with the requirement to certify the LM for crewed test flights satisfied, a potential second unmanned test flight with LM-2 was cancelled allowing one more mission to be cut from the Apollo program’s increasingly tight schedule. With LM-2 being unsuitable for manned flight without significant reworking to meet new requirements in the wake of the Apollo 1 fire, it was set aside as work continued on LM-3 for the first manned LM test flight (what would become Apollo 9 – see “Apollo 9: Giving the Spider Wings“). LM-2 would eventually be modified to mirror the configuration of the LMs which landed on the Moon and placed on display at the Smithsonian National Air & Space Museum. In the mean time, NASA was one step closer to the Moon and continued its push towards the first manned Apollo flights expected later in 1968.

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Related Video

Here is an excellent NASA documentary from 1968 on the Apollo 5 mission:

Related Reading

“SA-206: The Odyssey of a Saturn IB”, Drew Ex Machina, May 25, 2018 [Post]

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

“Apollo 4: The First Flight of the Saturn V”, Drew Ex Machina, November 11, 2017 [Post]

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

General References

Thomas J. Kelly, Moon Lander: How We Developed the Apollo Lunar Module, Smithsonian Institution Press, 2001

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

Apollo 5 First Lunar Module Test in Space, NASA Press Release 68-6, January 11, 1968

Apollo 5 Mission Report, MSC-PA-R-68-7, NASA Manned Space Center, March 1968

Final Flight Evaluation Report: Apollo 5 Mission, D2-117017-2 Rev C, NASA Office of Manned Space Flight, October 1968