SM-65D Atlas: Difference between revisions

The Atlas D testing program began with the launch of Missile 3D from LC-13 on April 14, 1959. Engine startup proceeded normally, but it quickly became apparent that the LOX fill/drain valve had not closed properly. LOX spilled around the base of the thrust section, followed by leakage from the RP-1 fill/drain valve. The propellants then mixed and exploded on the launch stand. Because of the open LOX fill/drain valve, the Atlas's propellant system suffered a loss of fuel flow and pressure that caused the B-2 engine to operate at only 65% thrust. Due to the imbalanced thrust, the Atlas lifted at a slanted angle, which also prevented one of the launcher hold-down arms from retracting properly. Subsequent film review showed that no apparent damage to the missile resulted from either the launcher release or the propellant explosion. The flight control system managed to retain missile stability until T+26 seconds when the loss of pressure to the LOX feed system ruptured propellant ducting and resulted in an explosion that caused the booster section to rip away from the missile. The Atlas sank backwards through its own trail of fire until the Range Safety destruct command was issued at T+36 seconds. The sustainer and verniers continued operating until missile destruction. All other missile systems had functioned well during the brief flight and the LOX fill/drain valve malfunction was attributed to a breakdown of the butterfly actuator shaft, possibly during the Pre-Flight Readiness Firing a few weeks earlier, so Atlas vehicles starting with Missile 26D would use an actuator made of steel rather than aluminum. The leakage from the fuel fill/drain valve was traced to an improper procedure during the prelaunch countdown and was not connected to the LOX fill/drain valve problem. LC-13 sustained some damage due to the anomalous liftoff of Atlas 3D, this was quickly repaired and preparations began for the launch of Missile 5D.<ref>"Flight Test Evaluation Report, Missile 3D." Convair, 29 April 1959</ref>

 

 

Atlas 5D lifted from LC-13 on June 6. The flight went perfectly until booster separation, at which point a fuel leak started. Tank pressure decreased until the intermediate bulkhead reversed at T+157 seconds and the missile exploded. This incident was similar in nature to an Atlas C failure earlier in the year and it resulted in a major investigation and redesign effort. The failure point was either the fuel staging disconnect valve or associated plumbing, and modifications were made to the disconnect valve, plumbing, booster separation system, jettison tracks, and even the launcher mechanism, all of which were possible causes of the malfunction. On July 29, Missile 11D was launched with a series of modifications designed to correct problems on previous Atlas launches. The flight was mostly successful and booster section separation was performed successfully on a D-series Atlas for the first time, but some difficulties with the hydraulic system occurred due to low engine compartment temperatures caused by a probable LOX leak. Missile 14D launched from LC-13 on August 11, at which point the Air Force somewhat reluctantly declared the Atlas to be operational as a missile system. On September 9, Missile 12D launched from Vandenberg Air Force Base, marking the first Atlas flight from the West Coast. Eight more D-series ICBM tests were conducted in 1959, as well as two space launches using Atlas D vehicles. Although assorted minor failures and hardware bugs affected these flights, the overall success rate was a major improvement over the first half of the year.

Atlas D tests on the West Coast hit a series of snags in the following months as well when IOC testing began. Atlas 25D had flown successfully on April 22 from 576B-1, a coffin silo, after delays following the postflight findings from 51D and 48D. The next attempt was 23D on May 6. Following a normal liftoff, control began to fail the moment the pitch and roll sequence began at T+21 seconds. The missile performed a couple of cartwheels before the Range Safety destruct command was sent at T+26 seconds. This failure was attributed to wiring in the pitch gyro contacting the casing and shorting out the gyro motor. The guidance system rate beacon also failed at liftoff, thus it would have been impossible to transmit any discreet guidance commands to the missile had the flight continued. Atlas 74D (July 22) broke up 70 seconds into launch due to a failure of the pitch gyro either due to an improper motor speed setting or torquing signals. Missile 47D (September 12) lost sustainer thrust starting at T+220 seconds due to an apparent loss of helium control pressure to the gas generator. The sustainer completely shut down at T+268 seconds and the missile fell 480 miles (772&nbsp;km) short of the target area. Making postflight analysis difficult was a major loss of telemetry data at T+109 seconds caused by a power failure, consequently only 13 telemetry measurements remained active for the rest of the flight. Missile 33D (September 29) failed to stage its booster section when the staging electrical disconnect plug pulled out at T+125 seconds; it impacted {{convert|1200|mi|km}} short of the target area. 81D (October 13) failed when the LOX quick disconnect pressure sensor malfunctioned due to the loss of a heat shield at liftoff. As a consequence, the tank pressurization system mistakenly sensed a drop in tank pressure and began pumping helium into the tanks to raise their pressure level. Pressures in both propellant tanks began rising at T+39 seconds and the missile self-destructed when excessive LOX tank pressure ruptured the intermediate bulkhead at T+71 seconds.<ref>"Flight Test Evaluation Report, Missile 81D October 27, 1960"</ref>

 

 

Five more Atlas D tests from CCAS during the year were successful, these were 76D, 79D, 71D, 55D, and 83D. Missile 79D was the last test flight from LC-14, which had otherwise been turned over to NASA for Project Mercury but the failure of Mercury-Atlas 1 in July caused a lengthy delay between flights and so LC-14 was temporarily free for use. The most notable flight in this stretch was Atlas 71D on October 13 which carried three mice and other experiments in a biological nose cone which successfully completed a {{convert|5000|mi|km|adj=on}} lob downrange from LC-11 at the Cape. This missile utilized a dry start method without any hold-down time at liftoff with no apparent ill effects and all airborne systems performed well aside from an unexplained decrease in B-1 and sustainer thrust a few seconds before BECO. This was attributed to a probable fuel line obstruction. Cameras mounted on the nose cone photographed the spent Atlas after capsule separation.<ref>"Flight Test Evaluation Report, Missile 71D." Convair, 29 October 1960</ref>

Atlas 90D, the final R&D flight of a D-series missile, launched successfully from LC-12 on January 23, 1961. Four operational Atlas D flights from VAFB during the year were successful and the first three flights of 1962 also went without a hitch. Atlas 52D launched from 576-B3 at VAFB on February 21, 1962. Abnormal thrust section temperatures occurred early in the flight, and the sustainer and verniers shut down starting at T+49 seconds. The booster engines experienced thrust decay at T+58 seconds followed by complete loss of thrust at T+68 seconds, and missile breakup five seconds later. This failure was traced to a leak in the booster engine gas generator that caused thrust section overheating and loss of engine thrust, and it occurred a mere five hours after [[John Glenn]]'s Mercury launch, driving home the point that Atlas was still far from a reliable vehicle.<ref>"Flight Test Evaluation Report, Missile 52D March 3, 1962"</ref>

 

 

===1963===