An Atlas D LV-3B launching Mercury-Atlas 6
Expendable launch system
|Country of origin||United States|
|Launch sites||LC-11, 12, 13 & 14, CCAFS
|First flight||14 April 1959|
|Last flight||7 November 1967|
The SM-65D Atlas, or Atlas D, was the first operational version of the U.S. Atlas missile. Atlas D missiles were also used for orbital launches, both with upper stages and on their own as a stage-and-a-half vehicle.
The Atlas D testing program began with the launch of Vehicle 3D from LC-13 on April 14, 1959. The right booster engine experienced problems at ignition, falling to only 40% of full thrust. Additional problems were caused when the LOX drain valve failed to close, oxidizer spilled down the side of the booster and exploded on contact with the engine exhaust. The vehicle lifted and continued to fly at an oblique angle for about 20 seconds before further explosions in the boattail section caused the right booster engine to separate from the Atlas. With all control lost, the burning missile pitched over and was destroyed by Range Safety at T+37 seconds. 
On May 18, Atlas 7D was prepared for a night launch. The test was conducted with the Mercury astronauts in attendance in order to showcase the vehicle that would take them into orbit, but 60 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 a pin on the right launcher hold-down arm, causing helium pressurization gas to escape so that the RP-1 tank overpressurized and ruptured the LOX tank above it.
Atlas 5D in June suffered loss of thrust at staging due to another valve problem, but the fifth test on July 29 was successful, and after another flight on August 11, the Atlas D was reluctantly declared operational. Subsequent tests in the fall and winter all performed well, although the launch of a boilerplate Mercury capsule on Atlas 10D (Big Joe) in September was a partial success because the booster engines failed to separate.
With this string of successful Atlas tests, NASA, Convair, and the Air Force were lulled into a sense of security that was rudely ended on March 13, 1960 when Atlas 51D suffered combustion instability and was destroyed by Range Safety only three seconds after liftoff. A second disaster occurred on April 8 when 48D experienced the same problem, but this time failed to make it off the pad before exploding, severely damaging it in the ensuing holocaust. With two launch facilities now in need of repair, attention shifted to LC-12 where Atlas 56D flew over 9000 miles with an instrumented nose cone, impacting the Indian Ocean.
Meanwhile, Missile 23D in May lost control shortly after liftoff from Vandenberg AFB due to an electrical short. There were multiple problems at Pad 576B with service tower umbilicals that were ultimately traced to erroneous construction of the pad itself.
Most Atlas D launches were sub-orbital missile tests; however several were used for other missions, including orbital launches of manned Mercury, and unmanned OV1 spacecraft. Two were also used as sounding rockets as part of Project FIRE. A number were also used with upper stages, such as the RM-81 Agena, to launch satellites.
 See also
- Encyclopedia Astronautica - Atlas
|This rocketry article is a stub. You can help Wikipedia by expanding it.|