Atlas B before the launch of SCORE (USAF)
Expendable launch system
|Country of origin||United States|
|Launch sites||LC-11, LC-13 & LC-14, CCAFS|
|First flight||19 July 1958|
|Last flight||4 February 1959|
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 section, in addition to an operational guidance computer. 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.
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+21 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 thrust section and part of the RP-1 tank remaining in one piece until impact with the ocean. Even before the flight was terminated, technicians had determined the cause of the failure - ground crews had forgotten to power on the yaw gyro during prelaunch preparations. To prevent a recurrence of this, Convair began equipping the gyroscope packages with motion sensors to ensure proper operation, something that would eventually become a standard part of guided missile control systems. Atlas 3B was considered "partially successful" because all other systems had functioned properly until missile destruction.
On August 2, Missile 4B, identical to 3B aside from minor venting changes, was successfully launched from LC-13 on a 2500-mile flight. All systems functioned normally and booster section separation, which was tested for the first time, occurred on schedule.
Missile 5B was launched successfully from LC-11 on August 29 and traveled 550 miles downrange, followed by 8B on September 14. Missile 6B broke the streak of successful flights on September 18 when it exploded 82 seconds after liftoff. The cause of the failure was traced to a seized turbopump, which resulted in abrupt termination of B-1 engine thrust at T+80 seconds, followed two seconds later by missile pitchdown and structural breakup.
The turbopump failure was a persistent problem that had plagued Thor, Jupiter, and Atlas launches, all of which used a variant of the same Rocketdyne engine and which had an extremely marginal turbopump design that resulted in the lubricant oil foaming at high altitude and causing the bearings in the pump to come loose, resulting in instant pump shutdown. The Army Ballistic Missile Division had replaced all of the turbopumps in their stock of Jupiter missiles and did not experience any turbopump failures after January 1958, but the Air Force resisted doing the same with Thor and Atlas missiles so as to not delay the test program. The result was that several pump-related failures occurred in the Thor and Atlas programs during 1958 and only after Atlas 6B did they finally give in and agree to replace the pumps.
Missile 9B, the first Atlas with upgraded turbopumps, was launched on November 18. Gyroscope problems struck again when a misaligned roll gyro caused an unplanned rolling motion of the missile shortly after liftoff, but the guidance system was able to correct the flight trajectory. Excessive fuel consumption led to premature sustainer shutdown and so the missile did not achieve its planned range of 3150 miles, instead managing only 2300 miles. BECO occurred at T+131 seconds and SECO at T+227 seconds, while nose cone separation was not accomplished. The malfunction was due to the turbopumps not being properly matched to the engines in the Atlas. Due to the need to test them out, there had not been any time to perform this step.
On November 29, Missile 12B was successfully launched from LC-14 and made a 6325-mile lob, the first full-range flight of an Atlas missile. This step was achieved a full six months earlier than originally anticipated by program plans.
On December 18, Missile 10B performed the first use of an Atlas for a space launch when it orbited SCORE, a prototype communications satellite. This Atlas included several modifications for the flight, including 5-second vernier start tanks. The missile was also stripped down to save weight--the Azusa tracking system, telemetry packages, and all other hardware not absolutely essential to the flight were removed. In addition, it was equipped with MA-1 engines that had been tested and found to have above-average performance. The launch was conducted with stringent secrecy, in part because the Air Force were concerned about another embarrassing public launch failure like Vanguard TV-3 the year before. In the event that SCORE failed, they could simply claim that it was an ICBM test, and most of the launch crew also did not know 10B's true mission, as the missile was shipped to CCAS carrying a standard blunt Atlas RV and only the night before the launch was the satellite mounted on top of it. Orbital launches required a considerably different flight path than missiles, and during launch, the Range Safety Officer, who assumed it was a routine Atlas missile test, almost pressed the destruct button on noticing that the trajectory was "off", but he was quickly talked out of it. SCORE transmitted a tape-recorded Christmas greeting from President Eisenhower and operated for 13 days until the batteries ran down. The satellite, which remained attached to the spent Atlas, decayed from orbit on January 21, 1959. With a combined weight of 8660 pounds (3928 kg), it held the record for largest manmade object in space for a number of years. The lack of a telemetry system meant that limited data on the missile's performance was available, however all systems appeared to operate correctly throughout powered flight. A slight rolling motion was attributed to a 10° misalignment of the roll gyro, however a backup command from the guidance system corrected it.
On January 16, 1959, Missile 13B, which was the backup booster for SCORE and carried the same modified hardware, was launched from LC-14 but lost thrust slightly under a minute into launch and fell into the Atlantic Ocean. The exact cause of the failure could not be determined because just like 10B, the missile was not carrying a telemetry package due to the intended mission of flying an Atlas to its maximum range, which required stripping the missile down to as light a weight as possible. Starting at T+100 seconds, the engines began gimbaling in all three axes, resulting in complete loss of control and missile tumbling. Propulsion system performance started decaying at T+109 seconds and the engines completely shut down at T+121 seconds. The missile remained structurally intact until impact with the ocean. The failure was believed to have been caused by exhaust gases being sucked into the thrust section and burning through wiring.
The Atlas B test program concluded with the fully successful flight of Missile 11B on February 4, which traveled 610 miles downrange.
|1958-07-19||17:36||LC-11||3B||10 km (6.2 mi)||Failure.||Flight control failure due to the launch crews forgetting to power on the gyroscope package. Missile broke up T+43 seconds. Flight considered a "partial success" because the propulsion system functioned normally until vehicle breakup.|
|1958-08-02||22:16||LC-13||4B||900 km (560 mi)||Success|
|1958-08-29||04:30||LC-11||5B||900 km (560 mi)||Success|
|1958-09-14||05:24||LC-14||8B||900 km (560 mi)||Success|
|1958-09-18||21:27||LC-13||6B||100 km (62 mi)||Failure.||Turbopump failure followed by missile self-destruction at T+82 seconds.|
|1958-11-18||04:00||LC-11||9B||800 km (500 mi)||Partial failure.||Excessive fuel consumption by the sustainer engine led to premature cutoff. This vehicle was equipped with redesigned turbopumps following the failure of Missile 6B.|
|1958-11-29||02:27||LC-14||12B||900 km (560 mi)||Success||First full-range test flight|
|1958-12-18||22:02||LC-11||10B||N/A||Success||Placed SCORE satellite into 185 km x 1,484 km x 32.3° orbit. First use of an Atlas for a space launch. Vehicle 10B included several custom modifications for this flight.|
|1959-01-16||04:00||LC-14||13B||100 km (62 mi)||Failure.||Loss of thrust at T+121 seconds due to suspected overheating in the thrust section (there was no telemetry system on this missile).|
|1959-02-04||08:01||LC-11||11B||900 km (560 mi)||Success|
- Encyclopedia Astronautica - Atlas B
- "Flight Test Evaluation Report, Missile 3B." Convair, August 2, 1958
- "Flight Test Evaluation Report, Missile 6B." Convair, October 1, 1958
- "Flight Test Evaluation Report, Missile 9B." Convair, December 5, 1958
- "Flight Test Evaluation Report, Missile 10B." Convair, January 4, 1959