Little Joe 1A

Little Joe 1A's story begins with somebody else's failure. On 21 August 1959, at Wallops Island, NASA was counting down to the first scheduled launching of a Little Joe vehicle. Thirty-five minutes before the appointed time the area evacuation was proceeding on schedule and the batteries for the programmer and the destruct system in the test booster were being charged. Half an hour before launch time there was an explosive flash. When the smoke cleared it was evident that only the capsule-and-tower combination had been launched, on a trajectory much like an off-the-pad abort; the booster and the adapter clamp ring were still intact on the launcher. Near apogee, at about 2,000 feet, the ring holding tower to capsule released and the small pyrotechnic tower-jettison rocket fired. The capsule came down about 2,000 feet from the launch site.

The accident report, issued on 18 September 1959, blamed the premature firing of the escape rocket on an electrical leak — what missile engineers called transients, or ghost voltages, in a relay circuit. The fault was traced to a coil. The flight, logged as LJ-1, lasted about twenty seconds, reached four tenths of a statute mile in altitude and landed half a mile from the launcher. Nothing that was meant to be measured got measured.

What was meant to be measured was the very heart of Mercury's crew safety system. LJ-1's objective was to determine how well the escape rocket would function under the most severe dynamic loading conditions anticipated during a Mercury-Atlas launching: the moment when the stack passes through maximum dynamic pressure, the point at which an emergency separation is hardest and most dangerous. Without that data no astronaut could ride an Atlas with any assurance that the tower would pull him clear. The test remained outstanding and had to be repeated. The repeat was called Little Joe 1A.

The Little Joe vehicle was conceived for exactly this. Its bidders' briefing was held on 21 October 1958, within the development phase of the manned satellite project. It was a deliberately simple rocket: 48 feet tall, 6.66 feet in diameter, weighing at most 41,330 pounds, with a cluster of eight solid-fuel motors — four Pollux and four Recruit — developing 250,000 pounds of thrust and able to lift a maximum payload of 3,942 pounds. No turbopumps, no cryogenic propellants, none of the pad time an Atlas demanded: it went up on a launcher at Wallops Island and it was fired.

Its cheapness was a programme virtue, not an accounting footnote. The whole Little Joe development effort was funded out of transfers to the Langley Research Center, at a total programme cost recorded in the Mercury chronology that was a tiny fraction of what a test with an operational missile cost. In exchange, Little Joe could reproduce the dynamic pressure profile of a Mercury-Atlas ascent through the handful of seconds that mattered, which were the only seconds that mattered for testing the escape tower. NASA could afford to lose one and try again — and that is precisely what happened with LJ-1.

Wallops Island supplied the other half of the equation: an agency facility on the Virginia shore, with the Atlantic in front of it for recovery and none of the competition for pads and windows that ruled at Cape Canaveral. Every Mercury Little Joe flight departed from there.

Little Joe 1A flew with a formal objective list more ambitious than simply repeating LJ-1. The first and principal one was to carry out a planned abort of the spacecraft from the booster at the maximum dynamic pressure anticipated during a Mercury-Atlas exit flight. The rest made the most of the ride: to obtain added reliability data on the operation of the Mercury drogue and main parachutes; to study the spacecraft's impact behaviour on the water; to gain further operational experience in recovering a floating spacecraft with a surface vessel; to gain further experience and confidence in the operation of the booster command thrust termination system; and to recover the escape motor and tower for examination.

That list says a good deal about the programme's philosophy in 1959. An eight-minute uncrewed flight was never devoted to a single question: every question that would fit was loaded onto it, because each launch was expensive in schedule even when it was cheap in money. Recovering the escape motor and tower, in particular, followed directly from the August disaster: after a spontaneous ignition blamed on an electrical circuit, having the hardware back on the bench was worth as much as the telemetry.

The payload was a boilerplate spacecraft, a structural stand-in for the Mercury capsule without crew systems, and the booster was the third Little Joe built. There was no crew and no primate aboard.

The launch took place on 4 November 1959 from the Wallops Island pad. The planned sequence ran as follows: after lift-off, the pressure sensing system was to supply a signal when the intended abort dynamic pressure was reached, about thirty seconds after launch. That signal became an electrical impulse which fired the explosive bolts separating the spacecraft from the launch vehicle and, at the same instant, started the igniter in the escape motor. Normally, capsule and tower would then be flung forward at the moment of maximum aerodynamic load — precisely what the system would have to do if an Atlas failed with an astronaut aboard.

Up to separation everything went as planned. The sensor detected the condition, the impulse went out, the explosive bolts fired and the spacecraft came free of the booster. The escape motor igniter activated as well. But pressure failed to build up in the motor until a number of seconds had elapsed. By the time the escape motor really pushed, the capsule was no longer at maximum dynamic pressure: the abort manoeuvre, the prime mission of the flight, was accomplished at a dynamic pressure that was far too low.

The flight numbers make it plain. Maximum dynamic pressure recorded was 168 pounds per square foot, where the environment to be reproduced was the roughly 1,000 pounds per square foot of an Atlas ascent. Peak acceleration reached 16.9 g. The spacecraft attained an altitude of 9 statute miles — 47,520 feet — and a range of 11.50 statute miles, at a maximum speed of 2,021.6 miles per hour, equivalent to 2,040 feet per second earth-fixed and 2,965 feet per second space-fixed. The whole flight lasted eight minutes and eleven seconds.

Apart from the escape motor anomaly, the account of the flight is remarkably dull, and that was good news. All other events from launch through recovery occurred without incident. Drogue and main parachutes worked and delivered the reliability data sought; the capsule survived water impact, floated and was recovered by a surface vessel, so the maritime recovery exercise was accomplished; and the booster's command thrust termination system added another correct performance to its record.

NASA logged the mission as a partial success. The label is accurate and worth reading carefully: this was not a vehicle failure, nor a spacecraft failure, nor an accident. It was a test executed in full but at the wrong point on the trajectory, so that the question behind the flight — will the escape tower hold and work with an Atlas aerodynamic load on it? — went unanswered. In the agency's own later account, though the launch and recovery were successful, researchers were not able to test the escape system at maximum aerodynamic loads on this flight.

For that reason a repeat of the test was planned. It came on 21 January 1960 as Little Joe 1B, a flight of almost identical profile: 49,104 feet of altitude, 11.70 statute miles of range, the same 2,021.6 miles per hour of maximum speed, and eight minutes thirty-five seconds of duration. The Little Joe chain continued with LJ-2 on 4 December 1959 — a planned escape at high altitude, around 96,000 feet, just before main booster burnout, with a rhesus monkey aboard to measure the physiological effects of acceleration and weightlessness — and then, in 1960 and 1961, with LJ-5, LJ-5A and LJ-5B, once again devoted to the maximum dynamic pressure abort, this time using production Mercury spacecraft rather than structural mock-ups.

That persistence measures the real difficulty of the problem. Between LJ-1, LJ-1A, LJ-1B, LJ-5, LJ-5A and LJ-5B, the programme spent six flights on a single matter: proving that the tower could pull an astronaut off a rocket in the worst possible second. None of those flights took anybody anywhere, and every one of them was a precondition for anybody going at all.

Little Joe 1A occupies an awkward slot in the programme's tables: the flight that had to be made because the previous one never left the launcher, and that had to be repeated because the escape motor lit late. Its real balance sheet, though, is better than its label. It put the escape system back through a complete flight after the August 1959 scare, validated separation by explosive bolts, added parachute, impact and flotation data, exercised recovery by ship and confirmed the command thrust termination cut-off. All of that went into the credit column and never had to be demonstrated again.

Seen from the end of the series, NASA's verdict on the whole is the fitting one: subsequent launches were successful and the Little Joe programme proved the general concept of the Mercury system to be sound. LJ-1A is not the test that closed that question, but it is the flight in which the programme got moving again after its first public stumble, and the one that pinned down precisely the single point still left to verify.