The Infamous Launch Abort of NASA’s Mercury-Redstone 1

While launching crews into orbit has become routine with even commercial companies beginning to provide lift services for customers like the US government, it was far from routine decades ago during the opening years of the Space Age. At that time, teams of the best scientists and engineers in the US and the old Soviet Union struggled to develop and master the new technologies required to safely send people into space resulting in numerous failures. One of the most infamous of these failures was the launch abort of NASA’s Mercury-Redstone 1 which was meant to test the rocket and spacecraft which would send the first Americans into space.

Artist concept of the Mercury capsule with its launch escape system. (NASA)

The Mercury-Redstone

Begun shortly after its founding in October 1958, the goal of NASA’s Project Mercury was to send a single astronaut into orbit using a modified version of the Atlas D ICBM – the largest rocket the US had available at the time (see “The Origins of NASA’s Mercury Program”). As the end of 1960 was approaching, NASA had already launched a pair of test flights of the Mercury-Atlas with less than stellar results. The first test flight launched on September 8, 1959, dubbed “Big Joe”, used a modified production Atlas D to launch a boilerplate Mercury capsule on a suborbital test flight. Although significant problems were encountered with the launch vehicle and the spacecraft, most of the flight’s objectives were met including testing Mercury’s then-innovative ablative heat shield during reentry into the atmosphere (see “Giving Mercury Its Wings: The First Test Flights of NASA’s Mercury Program”). The second test flight, Mercury-Atlas 1 (abbreviated MA-1), was launched on July 28, 1960 carrying the first production Mercury capsule for its first flight into space. Unfortunately, the Atlas 50D launch vehicle disintegrated during ascent less then a minute after launch (see “The Disappointing Flight of NASA’s Mercury-Atlas 1”).

The launch of Mercury-Atlas 1 from LC-14 on July 29, 1960. (NASA)

As NASA and the prime contractor of the Atlas, Convair, struggled to correct the problems uncovered by these test flights, focus turned to the first test flight of the Mercury-Redstone. The Redstone, which was only a quarter of the size of the Atlas, was intended to boost the manned Mercury spacecraft for 15-minute suborbital test flights which would precede the manned orbital flights. This would allow not only the spacecraft but its pilot to be evaluated during brief periods of weightlessness before committing to the longer orbital missions.

A comparison of the Redstone missile, the Jupiter-C/Juno I and Redstone Mercury Launch Vehicle. (NASA/MSFC)

The Chrysler-built Redstone was a short range tactical missile developed by a team at the ABMA (Army Ballistic Missile Agency) in Huntsville, Alabama under the direction of Wernher von Braun (see “Redstone: The Missile that Launched America into Space”). Since its inception in August 1953, the Redstone had been developed into a highly reliable rocket. A modified version of the Redstone was used by the von Braun and his team as the basis of the Jupiter-C/Juno I launch vehicle that sent America’s first satellite into orbit (see “Explorer 1: America’s First Satellite”). The version of the Redstone to be used for the Mercury program, known as the Redstone MRLV (Mercury Redstone Launch Vehicle), started with the Redstone variant with the stretched propellant tanks used on the Juno I rocket. But instead of using the highly corrosive and toxic Hydyne as a fuel, the Redstone MRLV reverted to the lower-performance (and safer) 75% ethanol mixture in combination with liquid oxygen (LOX) used in the production Redstone model. These propellants would feed a Rocketdyne A-7 engine (the latest version being used on production Redstone missiles) to generate 350 kilonewtons of thrust for about 145 seconds. The MRLV-variant of the Redstone was 1.8 meters in diameter and stood 25.4 meters tall with a launch mass of about 30 metric tons. In all, a total of 800 changes would be made to the Redstone to make it suitable for supporting crewed flights.

Diagram of the Redstone MRLV. Click on image to enlarge. (NASA)

The Plan

Just as with the earlier MA-1 mission, the first Mercury-Redstone mission (dubbed “Mercury-Redstone 1” or “MR-1”) used a production Mercury spacecraft manufactured by McDonnell Aircraft Corporation in St. Louis. Spacecraft No. 2 was assigned to the MR-1 mission and would include all of the systems need for a crewed mission, unlike Spacecraft No. 4 flown on MA-1 which did not include critical items like life support or an attitude control system. Unlike the orbital versions of the Mercury spacecraft which used an ablative heat shield, Spacecraft No. 2 was fitted with a 1.89-meter in diameter beryllium heatsink like the other suborbital Mercury capsule variants since the total reentry heat load during the suborbital missions was only 2% that for a return from orbit. The spacecraft was instrumented to monitor its systems and transmit telemetry live or record it onboard along with a 16 mm movie camera which would monitor the instrument panel readings during flight. Also carried was a 70 mm camera to document the view out of the capsule’s porthole and a cosmic ray film pack to measure exposure during the flight. The total launch mass of Spacecraft No. 2 was 1,290 kilograms, not including the launch escape tower.

Mercury Spacecraft No. 2 (in front) shown during assembly at McDonnell in St. Louis before its flight on Mercury-Redstone 1. (Boeing)

The plan for the Mercury-Redstone 1 mission was to launch the Mercury spacecraft into a suborbital trajectory with an apogee of 209 kilometers which would then reenter the atmosphere to splashdown 378 kilometers downrange in the Atlantic after a flight of 15.8 minutes. The objectives of this test flight included testing the Mercury spacecraft during about 5.2 minutes of weightlessness followed by a reentry with peak braking loads of about 11 g. The retrograde rockets, used to return a Mercury capsule from orbit, would be tested in flight for the first time during this mission as would the smaller posigrade rockets used to separate the capsule from it launch vehicle. Production-model descent and recovery systems would be tested as well. This would also be the first spaceflight of the Mercury to include the 468-kilogram launch escape tower which would be used to pull the Mercury capsule safely away from its launch vehicle in case of an abort during ascent.

A schematic showing the typical suborbital trajectory of the Mercury-Redstone. Click on image to enlarge. (NASA)

The Launch Attempt

When Mercury program managers drew up its first test schedule in January 1959, the Mercury-Redstone 1 flight was optimistically penciled in for launch in October 1959. Delays in spacecraft construction and certification eventually pushed this overly ambitious launch date out a whole year. In the mean time, pressure on Project Mercury only increased when the Soviet Union launched a prototypes of its crewed spacecraft in 1960 (see “Korabl-Sputnik & The Origin of the Soviet Vostok Program” and “Korabl-Sputnik 2: The First Animals Recovered From Orbit“), not to mention the failure of Mercury-Atlas 1.

The first piece of mission hardware to arrive at Cape Canaveral was Spacecraft No. 2 on July 23, 1960 after it had completed three weeks of tests with its assigned Redstone MRLV, designated “MR-1”, at the ABMA facilities in Huntsville, Alabama (which was formally transferred to NASA to become the Marshall Space Flight Center on July 1). Extensive reworking of various spacecraft systems was required as the fully-functional capsule was checked out at the Cape for its mission. In the mean time, the MR-1 launch vehicle arrived at the Cape on August 3 and, following its preflight checkout, was erected on the pad at Launch Complex 5 (LC-5) on August 22. Following being placed into temporary storage as Tropical Storm Florence passed Florida, MR-1 was re-erected at LC-5 on September 26 followed by the first mating of Spacecraft No. 2.

Spacecraft No. 2 shown being raised for mating with MR-1 at LC-5 in preparation for the Mercury-Redstone 1 mission. (NASA)

Following initial systems checks, the capsule was demated for additional work to correct ongoing problems. With this work completed on October 7, a launch date of November 7 was set. On October 24, MR-1 and Spacecraft No. 2 were mated for a second time with the final mating, following minor modifications and preparing the capsule for flight, taking place on October 31. The first launch attempt on November 7 was scrubbed at the T-22 minute mark when a leak developed in the capsule’s hydrogen peroxide-fueled attitude control system. The spacecraft was subsequently removed and sent back to the hanger so that the attitude control system’s helium relief valve and its toroidal hydrogen peroxide tank could be replaced.

Mercury-Redstone 1 shown being prepared for launch. (NASA)

With repairs completed, Spacecraft No. 2 was mated with MR-1 for a final time for a launch attempt on November 21. The countdown proceeded normally save for a one-hour hold to fix yet another, this time minor, leak in the hydrogen peroxide system. At 8:59 AM EST, the A-7 rocket engine of MR-1 ignited and began to lift off of its launch pedestal at LC-5. But to the horror of the personnel in the blockhouse monitoring the launch, the Redstone’s main engine shutdown almost immediately with the fully loaded launch vehicle settling back on its pedestal after rising a mere ten centimeters. As everyone held their breath, the launch escape tower was jettisoned followed by the deployment of the spacecraft’s drogue chute three seconds later then its main and reserve parachutes. Fortunately, the spacecraft’s posigrade and retrograde motors did not fire probably avoiding a pad explosion in the process.

The launch escape tower on Mercury-Redstone 1 being jettisoned after the rocket shutdown its main engine and settled back on its launch pedestal. (NASA)

The Aftermath of the MR-1 Failure

While the Mercury-Redstone 1 stack seemed safe at the moment, a debate broke out about what to do with the fully fueled, live rocket whose destruct system and other pyrotechnics were still live. In the end it was decided to do nothing until the following morning allowing the battery in the booster destruct system to deplete itself as well as the LOX in the Redstone to boil off. With the spacecraft relatively safe, crews carefully moved on November 22 to drain the ethanol from the rocket and roll the gantry back into place to safe the stack and evaluate the hardware. Except for the deployment of its parachutes, Spacecraft No. 2 was undamaged and could be reflown after being serviced. The MR-1 launch vehicle, however, damaged its fins (upon which the rocket sat) and there were signs of minor buckling in the skin of the rocket. MR-1 was removed from the pad and returned to Huntsville for a fuller evaluation and repair for potential reflight. The launch escape tower had buried itself in the sand 360 meters from the launch site after it had reach a peak altitude of 1,200 meters.

Workers shown next to the launch escape tower buried in the sand 360 meters from the launch site. (NASA)

Within two days, the investigation of this demoralizing failure had determined the cause of the malfunction and the reasons for the subsequent events. The problem was traced to a pair of electrical connectors located at Redstone’s Fin II at the base of the rocket which had disconnected at launch in an order that was reversed from a normal Redstone launch. Normally during launch, a 60-pin control connector unplugs before a four-pin power connector. During the erection and alignment of MR-1, a longer control cable from a tactical Redstone missile was substituted for the specially manufactured short cable meant for use on the Redstone MRLV. While the longer cable was blocked and clamped to shorten it, it was not shortened by enough. Because of the improper mechanical adjustments, the power plug disconnected 29 milliseconds before the control plug allowing 3 amps of current to flow inadvertently through engine’s “normal cutoff” relay for 40 milliseconds instead of to ground as would normally happen when the rocket was on the pad. This caused the engine to shutdown and triggered the automatic jettisoning of the launch escape tower. With the capsule’s recovery system now also armed, the barostatic switch which would trigger the deployment of the drogue chute at 12,800 meters was tripped followed by the main parachute which was triggered to deploy at 3,000 meters. Fortunately the 0.25 g gravity switches which inhibit the firing of the posigrade and retrograde motors were still active averting a total disaster.

Diagram showing the placement of the power and control connectors on the Redstone launch pedestal on Fin II (on right). A ground strap (indicated) was added after the failure to Mercury-Redstone 1 to prevent a recurrence of its launch abort. Click on image to enlarge. (NASA)

With the cause of the failure found, changes were made to the Redstone, its launch pedestal, Mercury spacecraft as well as ground procedures to prevent a recurrence of the problem. Spacecraft No. 2 was refurbished and replacement hardware diverted to support another launch attempt for “Mercury-Redstone 1A” scheduled for December 19.

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General References

Jerome B. Hammack and Jack C. Haberlick, “The Mercury-Redstone Program”, American Rocket Society Space Flight Report to the Nation (New York Coliseum; October 9-15, 1961), 1961

Loyd S. Swenson Jr., James M. Grimwood and Charles C. Alexander, This New Ocean: A History of Project Mercury, NASA SP-4201, 1966

“First Mercury-Redstone Flight Test Fails on Pad”, Aviation Week & Space Technology, Vol. 73, No. 22, pp. 28-29, November 28, 1960

“Second MR-1 Test Planned in Two Weeks”, Aviation Week & Space Technology, Vol. 73, No. 23, pp. 30-32, December 5, 1960

Mercury Capsule No. 2 Configuration Specification (Mercury-Redstone No. 1), Report No. 6603-2, McDonnell Aircraft Corporation, Revised February 6, 1961

The Mercury-Redstone Project, TMX-53107, NASA MSFC, December 1964