Probably one of the most dangerous phases of a space mission is launch which is why almost all crewed spacecraft have had launch abort options to cover all phases of ascent. In order to support abort options on the pad through the earliest parts of the flight, many crewed spacecraft have included a launch escape system (LES) consisting of an independent propulsion package to pull the crew capsule off of a malfunctioning launch vehicle and to safety. In over half a century of crewed spaceflight, the LES was used only once for the “Soyuz T-10A” pad abort in 1983 (see “Soyuz T-10A: The First Crewed On-Pad Abort”). The American Apollo, like the earlier Mercury spacecraft, also employed a LES but, to ensure that it would work as intended (especially in the early days of the Space Age before the availability of sophisticated computer simulation software), its design had to be verified through a series of ground and flight tests.
Testing the Apollo LES
The Apollo Launch Escape System (LES) was built by the Lockheed Propulsion Company (whose corporate parent is now part of Lockheed Martin). It consisted of a rocket motor assembly attached to the top of the Apollo Command Module (CM) by means of a truss framework with a total height of 9.9 meters and a mass of 4,200 kilograms. The main propulsion system of the LES of consisted of a solid rocket motor fitted with four nozzles that produced a nominal thrust of 650 kilonewtons for four seconds to lift the CM and LES away from the launch vehicle in case of an abort situation on the pad or during the initial phases of ascent. It also included a deployable canard system and a pitch motor rated at 18 kilonewtons to help stabilize the CM/LES during an abort and steer it out of the path of the malfunctioning launch vehicle. A smaller solid rocket motor with a pair of nozzles producing about 140 kilonewtons of thrust was used to pull the LES off of the ascending Apollo spacecraft when it was no longer needed to support abort options about three minutes after launch.
Diagram illustrating the major components of the Apollo Launch Escape System (LES). Click on image to enlarge. (NASA)
In order to test Apollo hardware under the most stressing flight conditions that it would experience during an abort situation at high altitudes and velocities, NASA contracted the production of the Little Joe II rocket. The original Little Joe was developed to perform abort tests in support of the Mercury program starting in 1959 (see “Giving Mercury Its Wings: The First Test Flights of NASA’s Mercury Program“). The Little Joe was meant to be a simple, adaptable and inexpensive launch vehicle that would employ various combinations of readily available solid rocket motors firing together or in a preplanned sequence to lift test hardware to a desired speed and altitude to exercise the LES under a range of stressing abort situations. On May 11, 1962, the Convair Division of General Dynamics got the contract to develop and build the larger Little Joe II to support the Apollo program.
Diagram showing the typical configuration of the Apollo-Little Joe II. Click on image to enlarge. (NASA)
The Little Joe II was a fin-stabilized rocket with the same 3.96-meter diameter as the Apollo CM it was to lift. With the Apollo CM, a dummy service module (SM) and LES in place, the Apollo-Little Joe II had a total height of 26.2 meters. The internal configuration of the Little Joe II allowed up to seven Aerojet General Algol 1D solid rocket motors to be carried with each producing 465 kilonewtons of thrust for 40 seconds. Similar Algol motors were used as the first stage in NASA’s Scout all-solid launch vehicle. Up to six smaller Recruit solid motors could also be carried to provide a 1.5 second kick to aid in liftoff. By varying the number and firing sequence of all these motors, a large range of abort situations could be simulated to altitudes as great as 60,900 meters (although none of the Apollo abort tests would actually fly that high).
An exploded view of the Little Joe II and its major components. Click on image to enlarge. (NASA)
A typical test would have the Little Joe II lift the CM/LES combination to a desired altitude and velocity at which point the LES would pull the CM away from the rocket to perform the abort test and subsequent recovery sequence. The White Sands Missile Range (WSMR) in New Mexico was chosen as the launch site for the abort tests because of the increasingly busy schedule at Cape Kennedy hampered abort test scheduling. In addition, land recoveries were easier to perform and less expensive than water recoveries.
Diagram showing the events of a typical Apollo-Little Joe II abort test flight. Click on image to enlarge. (NASA)
Like the pair of pad abort test flights and the first Apollo-related orbital test flights using the Saturn I (see “The First Apollo Orbital Test Flight”), the first abort flights using the Little Joe II did not use actual Apollo flight hardware. Instead engineers employed boilerplate models which mimic the mass, shape and dynamic properties of actual flight hardware but otherwise only carried systems and instruments needed for the tests being conducted. Their low cost and adaptability made boilerplate models ideal for the first Apollo engineering test flights.
The First Abort Tests
After the first pad abort test on November 7, 1963 designated PA-1 which flew using Apollo BP-6 (Boilerplate number 6), the first test to use the Little Joe II was the Apollo A-001 mission (see “The First Apollo Little Joe II Launch”). Launched on May 13, 1964, Apollo A-001 met all of its test objectives despite the failure of one the three parachutes on BP-12 to deploy properly after reaching a peak altitude of 9 kilometers. This “anomaly” provided an unintended flight test of the CM to safely land using only two parachutes – a capability actually used during the recovery of the Apollo 15 Moon mission in 1971 when one of its parachutes failed to deploy properly.
BP-12 after its successful landing in the desert at the end of the Apollo A-001 flight on May 13, 1964. (NASA)
With the first Apollo Little Joe II flight under their belts, NASA engineers and contractors pushed forward with additional abort tests. The primary objective of the Apollo A-002 flight was to test the LES under the most stressing aerodynamic conditions at maximum dynamic pressure or “Max q” that approximated the limits of Apollo’s emergency detection system. This would also be the first flight to use a boost protective cover that would help protect the outer hull and windows of the Apollo CM during its initial ascent and jettisoning of the LES. For this test, BP-23 was used which had a total mass of 11,492 kilograms, including the LES. The Little Joe II for this flight used a pair of Algol solid rocket motors. Combined with four quick-burning Recruit motors to help get the 42,788-kilogram vehicle off the pad, the total lift off thrust of this configuration was 1,600 kilonewtons.
The launch of Apollo-Little Joe II A-002 on December 8, 1964 carrying BP-23. (NASA)
Apollo A-002 lifted off from Pad 36 at WSMR at 8:00:00 AM MST on December 8, 1964. During ascent, the Little Joe II initiated its “pitch up” maneuver 2.4 seconds earlier than planned subjecting the ascending vehicle to greater loads than intended. Still, the LES activated and pulled BP-23 away from its launch vehicle and reached a peak altitude of 15.35 kilometers above sea level. The CM’s recovery system was activated at an altitude of 7.16 kilometers and BP-23 safely landed in the New Mexico desert on its three parachutes 9.99 kilometers downrange after a flight lasting 7 minutes and 23 seconds. The only objective not met during the flight was that the new boost protective cover was damaged during the test indicating that the design was structurally inadequate. BP-23 was later refurbished to become BP-23A which flew the second (and last) pad abort test, PA-2, on June 29, 1965.
Pad abort test PA-2 flown on June 29, 1965 using the refurbished BP-23A. (NASA)
The next flight with the Little Joe II was Apollo A-003. The primary objective of this flight was to demonstrate the LES performance at an altitude approximating the upper limit for the system’s canard subsystem used to stabilize the LES and CM after an abort. For this flight, the Little Joe II was fitted with six Algol motors. With three of these motors ignited at launch (and the remainder during flight) this Little Joe II generated 1,395 kilonewtons of thrust at lift off in order to reach a peak altitude of 36.6 kilometers. The payload, with a total mass of 12,626 kilograms, consisted of BP-22 and its LES. This would be the most powerful configuration of the Little Joe II to fly and the heaviest with a launch mass of 80,372 kilograms.
Apollo-Little Joe II A-003 on its launch pad at WSMR before its launch on May 19, 1965 . (NASA)
The Apollo A-003 mission got underway at 6:01:04 MST on May 19, 1965. Just seconds after liftoff, the flight encountered trouble when the Little Joe II began to roll out of control before the second group of its Algol motors had a chance to ignite. The Little Joe II soon started disintegrating under the increasing loads and the LES was activated automatically only 26.3 seconds after launch with the roll rate of reaching a maximum 335° per second. BP-22 reached a peak altitude of only 6.04 kilometers and came down 5.55 kilometers downrange after a flight lasting only 5 minutes and 3 seconds. Despite the unplanned low altitude abort and the high roll rate that affected the performance of the LES canards (which can only operate effectively with roll rates less than 20° per second), the test flight managed to meet all of its objectives (footage of the breakup of the Little Joe II and subsequent abort during the A-003 flight can be found in the Related Video section below).
A montage of images showing the breakup and subsequent abort of the Apollo A-003 flight. Click on image to enlarge. (NASA)
The First Launch of Flight Hardware
After five abort test flights (including the pair of pad aborts), the Apollo LES had been subjected to a range of stressing conditions despite minor anomalies and an outright Little Joe II failure. For the final launch abort test, the primary objectives were to demonstrate the LES in the power-on tumbling boundary region and verify structural integrity with the CM at its design limits. Unlike the earlier abort tests which used boilerplates, a CM production model was to be flown – the first flight of actual Apollo spacecraft hardware. For the A-004 mission, the Block I Apollo CM-002 built by North American was flown which, with the boilerplate SM and LES, had a total mass of 14,717 kilograms – the heaviest payload ever carried by the Little Joe II. The Little Joe II for this test flight was configured to use five Recruit motors as boosters and four Algol motors – two ignited at launch and the other two ignited later during flight. The lift off thrust for this 63,381-kilogram vehicle was 1,766 kilonewtons – the highest of any Little Joe II flight.
The first Apollo CM to fly, CM-002, is shown being hoisted on top of a Little Joe II in preparation for the A-004 flight. (NASA)
After several delays due to technical difficulties and bad weather, the Apollo A-004 flight lifted off at 8:17:01 MST on January 20, 1966 from Pad 36 at WSMR. On schedule, the pitch up maneuver started upon ground command at Max q some 78.1 seconds after launch with the abort initiated 2.9 seconds later. During the abort, pitch and yaw rates reached a maximum of 160° per second while the roll rate reached 70° per second. The LES canards deployed on schedule and stabilized the CM with the aft heat shield forward after the vehicle had tumbled in flight about four times. The CM-002 spacecraft with the LES attached reached a peak altitude of 23.83 kilometers before arcing back down to Earth. The LES tower was jettisoned 194 seconds after launch with parachute deployment starting two seconds later. The first Apollo CM finished its flight 6 minutes and 50 seconds after launch with a successful touchdown 34.63 kilometers downrange. The Apollo A-004 mission carried the CM higher and farther downrange than any previous flight of the Little Joe II.
Apollo CM-002 shown after its landing in the desert at the end of the A-004 flight. (NASA)
After the successful A-004 mission, the CM-002 was refurbished and redesignated CM-002A. Originally to be used for air drop tests of the Apollo recovery system with actual flight hardware, the capsule was modified to become CM-002B when those tests were cancelled. Instead, CM-002B was used in a ground testing program to assess the effects of longitudinal vibrations during launch referred to as “pogo” on Apollo hardware. After this first piece of Apollo flight hardware to fly had completed its work, it was eventually refurbished and placed on display at the Cradle of Aviation Museum in Garden City, New York where it remains today. With the successful completion of the abort testing program, five orbital tests using the Saturn I using boilerplates (see “The Last Launch of the Saturn I”) and the first short flight of an actual CM flight model, the LES was now flight qualified and the Apollo spacecraft was ready for its first spaceflight this time using the new Saturn IB rocket.
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Related Video
This brief video includes footage of the breakup of Apollo-Little Joe II A-003.
Related Reading
“The First Apollo Little Joe II Launch”, Drew Ex Machina, May 13, 2014 [Post]
“The First Apollo Orbital Test Flight”, Drew Ex Machina, May 28, 2014 [Post]
“The Second Apollo Orbital Test Flight”, Drew Ex Machina, September 18, 2014 [Post]
“The Launch of Apollo A-103/Pegasus 1”, Drew Ex Machina, February 16, 2015 [Post]
“The First Apollo-Saturn Night Launch”, Drew Ex Machina, May 25, 2015 [Post]
“The Last Launch of the Saturn I”, Drew Ex Machina, July 30, 2015 [Post]
General References
David Baker, The Rocket: The History and Development of Rocket & Missile Technology, Crown, 1978
Courtney G. Brooks, James M. Grimwood and Loyd D. Swenson, Jr., Chariots for Apollo: A History of Manned Lunar Spacecraft, SP-4205, NASA, 1979
Mary Louise Morse and Jean Kernahan Bays, The Apollo Spacecraft – A Chronology Volume II, SP-4009, NASA
Neil A. Townsend, “Apollo Experience Report – Launch Escape Propulsion Subsystem”, NASA Technical Note D-7083, March 1973
Andrew, was the LES not used twice by Soyuz? Once for the pad abort, and once for the in-flight abort just before ASTP? And, of course, on the N-1…
The LES on “Soyuz 18A” in 1975 had already jettisoned its LES by the time it aborted its ascent. And yes, the LES on the N-1 was used but it was an unmanned launch (in fact, the LES had been employed during aborts of a number of unmanned test flights of the Soviet’s manned spacecraft and at least once on an American Mercury-Atlas flight)
I believe they actually reflew the Mercury capsule which was saved by the LES – you might even say that the famous failed liftoff was a reflight, too (just). I’d always assumed that the in-flight Soyuz sub-orbital abort used the LES, but, considering how far down range they landed, the spacecraft must have been going at a fair old belt (the problem arose when one of the boosters wouldn’t drop away, IIRC).
“the problem arose when one of the boosters wouldn’t drop away,”
Actually, the abort of Soyuz T-10A was caused by the failure of the Blok A core stage to separate properly (not one of the four booster Bloks). This abort is explained in detail in the following:
http://www.drewexmachina.com/2014/11/18/a-brief-history-of-launch-aborts/
An animation of the Little Joe disintegration https://66.media.tumblr.com/062368ebf113e98eb405c67e1399e8ad/tumblr_o7kzab47re1r4rwwwo1_500.gif
The actual Apollo 1. If you count the use of real production Apollo block 1 spacecraft. I actually researched this in the NASA Headquarters history archive. There was a lot of back and forth memoranda on this topic of how to proceed after Apollo 204 fire with the naming of missions. I think to avoid any controversy they just picked up with Apollo 4 and left unstated their logic.
Actually, the logic behind the “Apollo 4” mission designation is pretty straightforward: it was the 4th unmanned spaceflight of the Apollo program after the missions officially designated AS-201, AS-203, and AS-202 flown during 1966. The unofficial “Apollo 1” moniker for the original AS-204 manned mission didn’t affect things (save for avoiding the reuse of the “Apollo 1” name).