Mercury, America’s first manned spacecraft, had a solid-fuel rocket motor on a tower attached to the capsule’s nose for launch escape.  If the booster rocket malfunctioned the solid fuel motor would pull the spacecraft and its occupant to safety.  Before Mercury carried a human pilot into space, the launch escape system had to be thoroughly tested under the most extreme conditions anticipated.

To test the launch escape system, NASA engineers designed a rocket called the Little Joe.  Little Joe comprised an aluminum airframe built around a cluster of four modified Sergeant solid rocket motors called either Castor or Pollux depending upon the modifications.  Later in the design phase, four smaller Recruit motors were added to supplement the Castors.  The number of motors could be varied to tailor the particular fight profile to the desired test objectives.  Max Faget, the chief engineer for Mercury came up with the name “Little Joe” because the original arrangement of four solid fuel motors reminded him of the double deuce – a pair of twos – in dice, which is called little joe.  Motors could be ignited in sequential pairs, giving the Little Joe a “two-stage” ascent profile.

The North American Aviation Missile Division received a contract from NASA to construct the Little Joe airframes.  They built the rocket body from 0.10-inch aluminum.  Little Joe launches were made from Wallops Island, Virginia, a NASA research facility on the Atlantic coast.

There were seven Mercury Little Joe flights, the highest of which reached 53 miles.

Little Joe 1 (LJ-1) was scheduled for August 21, 1959.  The flight was supposed to test the launch escape system under high aerodynamic load conditions.  At first, everything proceeded smoothly with the countdown, until thirty-one minutes before launch, when the escape rocket unexpectedly fired.  Everyone in the immediate area scrambled for cover.  When the smoke cleared, they saw the Little Joe booster still there, minus the spacecraft, which landed about 2,000 feet away.  There had been a “sneak” circuit, or “ghost” voltage that fired the escape motor prematurely.

Little Joe 6 flew on October 4, 1959.  This flight was inserted into the program after the LJ-1 failure and used the booster planned for the first flight.  The purposes of this flight were to validate the structural integrity of the launch vehicle and spacecraft combination, check the operation of the launcher, and gather aerodynamic data. LJ-6 carried an inert launch escape motor. Four Pollux and four Recruit motors propelled LJ-6 to an altitude of 37 miles.

Launched on November 4, 1959, LJ-1A, a second attempt at the first mission, was considered a partial success because the escape rocket fired ten seconds too late and the aerodynamic loads were only a tenth of what had been desired.  Because preparations for the next flight were already far advanced, NASA managers decided to go ahead with the LJ-2 flight as planned.  The next attempt to test the launch escape system under maximum dynamic pressure would wait until January.  LJ-2, a test of the high-altitude escape performance, also carried the program’s first passenger.

The Space Task Group decided to test Mercury with Rhesus monkeys and chimpanzees before committing it to humans.  The chimpanzees came from the Aeromedical Field Laboratory at Holloman because they had a colony of apes there from other research programs.  The Air Force School of Aviation Medicine at Brooks Air Force Base in San Antonio, Texas, provided a pair of Rhesus monkeys for Little Joe flights.

LJ-2 carried Mercury’s first primate passenger on December 4, 1959.  The monkey, a male, was named “Sam” as an acronym for School of Aviation Medicine.  Fifty-nine seconds after launch, the abort sequence began.  LJ-2 was then at an altitude of 96,000 feet and a speed of Mach 5.5.  The spacecraft reached a peak of 53 miles before it landed in the Atlantic.  About two hours later the Navy recovered the capsule with its simian passenger.

NASA tried again to achieve the goals set for the first Little Joe flight with LJ-1B on January 21, 1960.  The capsule carried a female Rhesus, named “Miss Sam,” who was the backup for the original Sam.  Everything worked this time and the spacecraft reached an altitude of 9.3 miles and a speed of 2,021 miles per hour.  Miss Sam landed 11.7 miles downrange and she was successfully recovered almost immediately by a Marine helicopter.

Little Joe 5, launched on November 8, 1960, was the first to carry a production spacecraft.  Earlier Little Joe flights had used boilerplate capsules manufactured by Langley Research Center.  Fifteen seconds after launch, while the booster was still firing, the escape rocket prematurely ignited.  The spacecraft did not separate from the booster and the entire vehicle crashed into the ocean.

Little Joe 5A was launched on March 18, 1961.  The mission used production Mercury spacecraft #14. The LJ-5 failure sequence was repeated when capsule escape rocket again ignited prematurely with the capsule remaining attached to the booster. In this flight however, a ground command was sent to separate the capsule from the booster and escape tower. This allowed the main and reserve parachutes to deploy and the capsule was recovered with only minor damage. It would be used again on the subsequent Little Joe 5B mission; a third attempt to achieve mission objectives. The Little Joe 5A flew to an apogee of 7.7 miles and a range of 18 miles. The mission lasted 5 minutes 25 seconds. Maximum speed was 1,783 miles per hour and acceleration was 8 G.

Little Joe 5B reused spacecraft #14. The mission was launched April 28, 1961.  The Little Joe 5B flew to an apogee of 2.8 miles and a range of 9 miles. The mission lasted 5 minutes 25 seconds. Maximum speed was 1,780 mph and acceleration was 10 g. The mission was a success and Mercury spacecraft # 14A was recovered.

The first piloted Mercury flight, Freedom-7, carried Astronaut Alan B. Shepard, Jr. on a suborbital mission a week after the last Little Joe flight.

Written by Greg Kennedy on June 25th, 2013 , Space History

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