The SM-65D Atlas, or Atlas D, was the first operational version of the U.S. Atlas missile. Atlas D was first used as an intercontinental ballistic missile (ICBM) to deliver a nuclear weapon payload on a suborbital trajectory. It was later developed as a launch vehicle to carry a payload to low Earth orbit on its own, and later to geosynchronous orbit, to the Moon, Venus, or Mars with the Agena or Centaur upper stage.
Atlas D was launched from Cape Canaveral Air Force Station, at Launch Complexes 11, 12, 13 and 14, and Vandenberg Air Force Base at Launch Complex 576.
The fully operational D-series Atlas was similar to the R&D model Atlas B and C, but incorporated a number of design changes implemented as a result of lessons learned during test flights. In addition, the D-series had the full-up Rocketdyne MA-2 propulsion system with of thrust versus the of thrust in the Atlas B/C's engines. Operational Atlas D missiles retained radio ground guidance aside from a few R&D launches which tested the inertial guidance system designed for the Atlas E/F, and the Atlas D would be the basis for most space launcher variants of Atlas.
History
1959
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."Flight Test Evaluation Report, Missile 3D." Convair, 29 April 1959
On May 18, Atlas 7D was prepared for a night launch of an RVX-2 reentry vehicle from LC-14, the second attempt to fly one after the launch of a C-series Atlas had miscarried two months earlier. The test was conducted with the Mercury astronauts in attendance in order to showcase the vehicle that would take them into orbit, but 64 seconds of flight ended in another explosion, prompting Gus Grissom to remark "Are we really going to get on top of one of those things?" This failure was traced to improper separation of the right launcher hold-down pin, which damaged the B-2 nacelle structure and caused helium pressurization gas to escape during ascent. At 62 seconds into the launch, the pressure in the LOX tank exceeded the pressure in the RP-1 tank, which reversed the intermediate bulkhead. Two seconds later, the missile exploded. Film review confirmed that the hold-down pin on the right launcher arm failed to retract at liftoff and was jerked from the missile. The resultant force caused a four-inch gap in the B-2 nacelle structure which also damaged low-pressure helium lines. The hold-down pin had not retracted due to a sheared retaining bolt in the bell crank pulley system in the right launcher arm. Once again, all other systems in the Atlas functioned well and there were no problems not directly attributable to the launcher malfunction. The flight of 7D resulted in improved maintenance procedures for the launcher equipment at CCAS and use of higher heat steel in the bell crank retaining bolts."Flight Test Evaluation Report, Missile 7D." Convair, 3 June 1959
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.
Missile 26D on October 29 experienced a premature shutdown of the V-1 vernier when interference from the onboard camera package caused temporary loss of ground guidance lock on the missile. Impact occurred short of the target point.
Because of growing confidence in the Atlas, it was decided to abandon PFRF (Pre-Flight Readiness Firing) tests except for the first handful of Atlas E flights as well as space launches. The final test of 1959, Missile 40D on December 19, utilized a "dry" start method (no inert fluid in the engine tubes). This experiment worked without any apparent problems. The first four Atlas flights of 1960, three CCAS and one VAFB launch, were largely successful. On 6D, several malfunctions of the ground guidance system occurred—spurious yaw commands were sent at T+175 seconds and ground guidance lock on the missile was lost for almost two minutes. The missile continued to be unstable in flight for the first 14 seconds of vernier solo phase. Furthermore, an erroneous VECO signal was sent at T+278 seconds but the missile programmer did not act on it due to an apparent open circuit. VECO was intended to take place at T+282 seconds but did not occur for the aforementioned reason and it was instead performed 12 seconds later by a backup signal generated by the programmer. The missile landed within of the target area."Flight Test Evaluation Report, Missile 6D." Convair, 10 February 1960
1960 On March 5, 1960, Missile 19D was undergoing a propellant loading exercise at 576-A2 at VAFB when a fuel leak started a fire on the pad that led to the explosion of the missile. The launch facility was written off due to the damage and not used again for almost 5 years.
On March 8, 1960, Missile 44D launched from LC-11 on the first test of the AIG (All Inertial Guidance System) and experienced a 90° roll transient at liftoff. The AIG managed to correct this problem and the missile completed a successful lob downrange."Flight Test Evaluation Report, Missile 44D." Convair, 29 March 1960
With this string of successful Atlas tests, program officials were lulled into a sense of security that rudely ended on March 11 when Atlas 51D lifted from LC-13. The B-1 engine suffered combustion instability which caused loss of thrust within two seconds of liftoff. An explosion ripped apart the thrust section, followed by structural failure of the propellant tanks, causing the Atlas to fall back onto LC-13 in an enormous fireball. The Atlas went in for a repeat performance on April 8 when Missile 48D, launched from LC-11 and intended as the first closed-loop test of the AIG (All Inertial Guidance System), experienced combustion instability again, this time in the B-2 engine. The first indication of trouble was a pressure surge in the B-2 combustion chamber, followed by unstable thrust, engine shutdown, and an explosion that started a thrust section fire. The B-1 engine then shut down, followed by the sustainer and verniers. Since the propulsion system had not attained sufficient thrust, the launcher hold-down mechanism did not release the missile, which stayed in place and burned on the pad. The thrust section fire slowed down 15 seconds after the attempted launch, then resumed around 45 seconds. At 60 seconds, the Atlas was completely destroyed when the propellant tanks exploded."Flight Test Evaluation Report, Missile 48D." Convair, 28 April 1960