January 07, 2005

Little Joe I

All images courtesy of NASA and are clickable for larger versions.

The Little Joe rockets were essential to the success of the US space programs, yet very few people know about them.

There were two basic models, known appropriately enough as Little Joe I and Little Joe II. Little Joe I was designed to test the emergency escape system of the Mercury capsules that would ride atop Atlas and later Redstone rockets. Little Joe II performed the same missions for the Apollo program.

The escape system itself was simple in concept, but depended on a complex sequence of events, so inflight testing was deemed necessary. Attached to the nose of the capsule was a framework with the escape rocket mounted at the very top. The escape rocket was a small but powerful solid fuel rocket with three exhaust bells canted out at an angle so that the flames didn't hit the capsule. The rocket burned for one second. On later Apollo's, a fifth rocket was added to the escape tower that fired directly sideways to push the capsule out of the way of the rocket it had been riding. The towers also carried a jettison rocket that ejected the tower away from the capsule once the boost phase of the flight was completed and the escape system was no longer needed.

Little Joe at Wallops Island.

Because each flight tested different aspects of the escape system, there was no standard configuration of the Little Joe rockets beyond the basic model. Various combinations of Pollux, Castor and small Recruit solid fuel motors were clustered together to craft a specific desired flight profile, and control ranged from simple fins to movable rudder surfaces or additional helper rockets designed to impart spin or other dynamic forces during flight. Each flight of a Little Joe I rocket could be accomplished for about 1/5 the cost of an Atlas flight.

The first Little Joe I launch was to take place from Wallops Island, Virginia in August, 1959. About a half hour before the scheduled takeoff, the escape rocket unexpectedly fired and carried the capsule to an altitude of about 2000 feet. The problem was traced to an electrical transient in the system that caused a premature abort signal. Even so, the escape sequence worked almost perfectly.

In October, 1959 the first Little Joe I flight took place from Wallops. Because the Little Joe flights were numbered according to mission goals and not chronologically, the first mission was LJ-6. This flight lifted a boilerplate Mercury capsule to an altitude of 40 miles and proved that the Little Joe rockets were suitable for the test series.

Sam after flight aboard Little Joe

The fourth Little Joe I launch tested the system at max-Q (maximum dynamic pressue) while carrying Miss Sam, a rhesus monkey*. At 9 miles altitude, the escape rocket fired and carried the capsule safely away from the rocket. Both Miss Sam and the capsule were recovered in perfect condition. In fact, at the later beach party it was agreed that the flight didn't affect the taste of the monkey meat at all (just kidding, checking to see who's paying attention).

The last of eight flights involved an actual malfunction of the Little Joe I rocket, yet the capsule was recovered in good shape. The series proved that the Mercury escape system would be effective in saving the astronaut's lives if called upon.

As for the how the rockets got their name, the original plans for the design showed four holes in a square pattern on the bottom where the booster motors would be attached. This pattern reminded the designers of the game of craps, where rolling the dice and getting a pair of dueces was called "little joe". The name stuck.

Part 2 covering the Little Joe II will be posted shortly.

Much of this material comes from Peter Alway's invaluable Rockets of the World, 3rd edition. Highly recommended.

See also Wikipedia and the Encyclopedia Astronautica for more information about the Little Joe and Mercury programs.

*Corrections: Miss Sam was the monkey who flew on the fourth Little Joe I flight. Sam, her male counterpart, made the flight on the 3rd launch of the Little Joe I. Both emerged from their test flights in fine shape, and Sam experienced 3 minutes of weightlessness at his apogee of 53 miles.

Posted by Ted at January 7, 2005 05:19 AM
Category: Space Program

Nice info. Thanks for posting it.

Posted by: JohnL at January 7, 2005 11:57 AM

...the flight didn't affect the taste of the monkey meat at all

If text books were written with little "wake-ups" like that, I would have pulled better grades.

Posted by: homebru at January 7, 2005 12:51 PM
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