The Convair SM-65B Atlas, or Atlas B, also designated X-12 was a prototype of the Atlas missile. First flown on 19 July 1958, the Atlas B was the first version of the Atlas rocket to use the stage and a half design with an operational sustainer engine and jettisonable booster engine section. Unlike later Atlas models, the Atlas B used explosive bolts to jettison the booster section. Ten flights were made. Nine of these were sub-orbital test flights of the Atlas as an Intercontinental Ballistic Missile, with five successful missions and four failures. The seventh flight, launched on 18 December 1958, was used to place the SCORE satellite into low Earth orbit, the first orbital launch conducted by an Atlas rocket.
Test history The B series test program took a considerable amount of delays and frustration, not in the least because the Atlas B was far more complicated than the prototype Atlas A, in fact the first launch would feature all hardware systems found on an operational Atlas, including the sustainer engine, separable booster section, guidance computer, Azusa tracking system, detachable nose cone, and more. The first flight article missile, 3B, was originally planned for launch in May 1958, but the date was set back by endless hardware difficulties, both with the missile itself and the newly opened LC-11. In addition, Atlas 3B could not be cleared for flight until a successful firing run of Missile 2B was performed at the Sycamore Canyon test stand, which was also experiencing nonstop technical issues. The launch of a third Soviet satellite in April also put further pressure on program planners. Finally, on July 19, Missile 3B was launched. Engine start proceeded normally and the launcher release system functioned well. The Atlas performed well until T+19 seconds when the programmer attempted to initiate the pitch and roll maneuver. At this point, the missile began swerving from side to side uncontrollably and finally broke up at the forward end of the LOX tank at T+43 seconds, the lower portion from the fuel tank downward remaining intact until impact in the ocean. Even before the flight had terminated, real time telemetry readouts clearly indicated that the fault lay in the yaw gyro motor, which was not running. To prevent a recurrence of this, Convair developed the Spin Motor Rotation Detection system, a collection of sensors designed to ensure proper gyroscope operation and which would prevent the launch if the motors were not running at the proper speed. It was not fully phased into Atlas vehicles until 1961 however. Atlas 3B was considered "partially successful" because all other systems had functioned properly. The only other abnormality was an unusually high usage of helium pressure gas, possibly due to a leak. If the flight had not terminated prematurely, the helium supply might have become depleted. Tank pressures however remained within normal levels until missile destruction. A minor thrust section fire was evident from T+9 seconds, caused by placement of the lube oil vent line near the booster turbine exhaust, however this was believed to have no connection to the subsequent loss of the missile. One telemetry channel failed during the prelaunch countdown, as a consequence 13 telemetry measurements were inactive during the flight.
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