SM-65D Atlas

Atlas D (SM-65D)

Launch sequence of an Atlas D ICBM test, April 22, 1960
Function	ICBM Expendable launch system
Manufacturer	Convair
Country of origin	United States
Launch history
Status	Retired
Launch sites	LC-11, 12, 13 & 14, CCAFS LC-576, VAFB
Total launches	135
Successes	103
Failures	32
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.

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 360,000 pounds of thrust versus the 275,000 pounds of thrust in the Atlas B/C's engines.

History

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 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 65% 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 the B-2 engine exploded due to combustion instability from the imbalanced fuel mixture, causing the complete destruction of the booster section. With the Atlas in flames and no longer controllable, the Range Safety destruct command was sent at T+35 seconds. The sustainer and verniers operated until missile destruction.^[1]

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 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.^[2]

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, intended as the first closed-loop test of the AIG (All Inertial Guidance System), 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 B-2 engine which backfired and ruptured from mechanical shock, starting a thrust section fire that led to the complete loss of the missile.^[3] 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. Missile 60D (July 2) returned to the dry start method, this time with a hold down period to check for combustion instability rather than immediately releasing the missile upon full thrust. While no on-pad explosion resulted on this attempt, the Atlas failed to complete all of its test objectives when the vernier start tanks were inadvertently vented and refilled several times during the flight. This resulted in depletion of control helium and loss of sustainer and vernier thrust near the end of powered flight, and so the Mark III Mod 1B reentry vehicle landed some 40 miles short of its intended target point. An electrical glitch was believed to have caused the unplanned start tank venting, although the specifics of could not be determined.^[4]

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 a failure of the pitch gyro. Missile 33D (September 29) failed to stage its booster section when the staging electrical disconnect plug pulled out at T+125 seconds. 81D (October 13) failed when the LOX pressure sensor malfunctioned, causing the pneumatic system to overpressurize the LOX tank with helium until it ruptured the intermediate bulkhead and destroyed the missile at T+72 seconds. Eventually it was discovered that the Atlas silos at Complex 576 had been constructed improperly with one pad umbilical installed in the wrong location. The effect of this was that the umbilical released prematurely at liftoff when it still had live electrical current in it (electrical power in the umbilicals was supposed to be shut off prior to disconnect) and ended up shorting components in the missiles. In the case of 23D and 74D, the pitch gyro motors had shorted out, causing loss of control in flight, and it had damaged other parts in 33D and 81D. The last Atlas flight of 1960, Missile 99D, was launched from 576-B3 and performed successfully in spite of the premature umbilical release. After this, the Complex 576 silos were not used again for a couple of months while the problem was corrected. On May 24, 1961, the complex returned to action when Missile 95D launched successfully from 576-B2.

Most failures after this point were high altitude or partial, and Atlas 90D's successful launch on January 23, 1961 concluded the R&D phase of the Atlas D program.

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.^[5]

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.

For Mercury, the Atlas D was used to launch four manned Mercury spacecraft into low Earth orbit.^[5] The modified version of the Atlas D used for Project Mercury was designated Atlas LV-3B.

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.

Warhead

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).

See also

• SM-65 Atlas

References

1. "Flight Test Evaluation Report, Missile 3D." Convair, 29 April 1959
2. "Flight Test Evaluation Report, Missile 7D." Convair, 3 June 1959
3. http://www.dtic.mil/dtic/tr/fulltext/u2/833337.pdf
4. "Flight Test Evaluation Report, Missile 60D." Convair, 15 July 1960
5. Encyclopedia Astronautica - Atlas