Launch sequence of an Atlas D ICBM test, April 22, 1960
Expendable launch system
|Country of origin||United States|
|Launch sites||LC-11, 12, 13 & 14, CCAFS
|First flight||April 14, 1959|
|Last flight||November 7, 1967|
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.
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 propulsion system with 360,000 pounds of thrust versus the 275,000 pounds of thrust in the Atlas B/C's engines.
The Atlas D testing program began with the launch of Vehicle 3D from LC-13 on April 14, 1959. Engine startup proceeded normally, but it quickly became apparent that the LOX fill/drain valve did not close properly. LOX spilled down the side of the missile, followed by leakage from the RP-1 fill/drain valve. The propellants mixed and exploded on the launch stand. Because of the fill/drain valves not closing properly, the Atlas's propellant system suffered a loss of fuel flow and pressure that caused the B-2 engine to operate at only 75% thrust level. 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, although subsequent review of film showed that the hold-down arm did not damage the missile. The flight control system managed to retain missile stability until T+26 seconds when leaking propellant ignited on contact with the engine exhaust and caused the booster section to explode. With the Atlas in flames and no longer controllable, the Range Safety destruct command was sent at T+35 seconds.
On May 18, Atlas 7D was prepared for a night launch of an RVX-2 reentry vehicle from LC-14. 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 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 the pneumatic system. The hold-down pin had not retracted due to a sheared retaining bolt in the bell crank pulley system in the right launcher arm.
Atlas 5D (June 6) performed well until booster separation at which point the fuel staging disconnect valve malfunctioned. Fuel tank pressure was subsequently lost, causing reversal of the intermediate bulkhead and missile self-destruction at T+157 seconds. On July 29, Missile 11D was launched successfully and included a number of modifications designed to correct problems on the previous Atlas D tests. After the flight of 14D in August, the Atlas D was declared operational. Subsequent tests in the fall and winter all performed well including the first Atlas launch from Vandenberg Air Force Base on September 9, 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. The high degree of success in late 1959-early 1960 boosted morale significantly after six failures in the first half of the year.
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 (engine igniter activated before propellant injection). This experiment worked without any apparent problems.
With this string of successful Atlas tests, including twin launches from Cape Canaveral and VAFB within hours of each other on January 26-27, 1960, program officials were lulled into a sense of security that rudely ended on March 11, 1960 when Atlas 51D lifted from LC-13. The B-1 engine suffered combustion instability, which caused the missile to "hover" above the launch stand. When it was apparent that the flight could not succeed, the range safety destruct command was sent, rupturing the propellant tanks and causing the Atlas to fall back onto the pad in a huge explosion, putting LC-13 out of commission for six months. The Atlas went in for a repeat performance on April 8 when Missile 48D exploded on LC-11 almost as soon as it was released by the pad hold-down arms due to another episode of combustion instability, this time in the sustainer engine, which backfired and ruptured from mechanical shock, starting a thrust section fire that ignited the propellant tanks. 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. LC-13 did not return to action until October when it hosted the first E-series Atlas launch. LC-11 meanwhile was operational after only two months and it hosted the successful launch of Missile 54D on June 11.
After the back-to-back pad explosions, it was decided to go back to using a wet start (propellants injected into the combustion chamber prior to ignition) on the Atlas rather than the failed experiment of a dry start to ensure smoother engine startup.
On May 6, 1960 Atlas 23D lifted from 576B-1, a coffin silo, at VAFB and began experiencing abnormal pitch gyrations within 10 seconds of launch. After about 20 seconds, the missile started tumbling out of control upon which the RSO sent the destruct command. The next flight, 74D (July 22) broke up 70 seconds into launch due to another control malfunction. Missile 33D (September 29) failed to stage its booster section and 81D (October 13) destroyed itself a minute into launch after the LOX tank overpressurized and ruptured the intermediate bulkhead. Eventually, it was discovered that the Atlas silos at VAFB had been constructed improperly with two pad umbilicals attached to the wrong location. This had caused the gyroscope packages in Missiles 23D and 74D to short out and led to other malfunctions in Missiles 33D and 81D.
Most failures after this point were high altitude or partial. Atlas 90D's successful launch on January 23, 1961 concluded the R&D phase of the Atlas D program. After an operational test in March 1963 (Missile 102D) suffered another control failure and RSO destruct shortly after liftoff, it was noted that the vehicle used a Type B gyro canister and all previous Atlases with them (Missiles 23D, 74D, and 17E) had failed as well. Another two missiles in VAFB's inventory were found to have these gyroscope packages, so they were promptly replaced with spares from the Mercury program and no guidance or control problems affected them during their flights.
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.
The Atlas D was deployed in limited numbers as an ICBM due to its radio guidance while the fully operational E and F-series missiles had inertial guidance packages and a different ignition system that allowed faster engine starts.
Atlas Ds used for space launches were custom-built for the needs of the mission they were performing, but when the Atlas was retired from missile service in 1965, Convair introduced a standardized Atlas vehicle (the SLV-3) for all space missions. Remaining D-series missiles were flown until 1967 for suborbital tests of reentry vehicles and a few space launches.
A total of 116 D-series missiles (not including vehicles used for space launches) were flown from 1959-67 with 26 failures.
The warhead of the Atlas D was originally the G.E. Mk 2 "heat sink" re-entry vehicle (RV) with a W49 thermonuclear weapon, combined weight 3,700 lb (1,680 kg) and yield of 1.44 megatons (Mt). The W-49 was later placed in a Mk 3 ablative RV, combined weight 2,420 lb (1,100 kg) The Atlas E and F had an AVCO Mk 4 RV containing a W-38 thermonuclear bomb with a yield of 3.75 Mt which was fuzed for either air burst or contact burst. The Mk 4 RV also deployed penetration aids in the form of mylar balloons which replicated the radar signature of the Mk 4 RV. The Mk 4 plus W-38 had a combined weight of 4,050 lb (1,840 kg).
- Encyclopedia Astronautica - Atlas