SM-65E Atlas

Atlas-E (SM-65E)

Launch of an Atlas-E missile
Function	ICBM Expendable launch system
Manufacturer	Convair
Country of origin	United States
Launch history
Status	Retired
Launch sites	LC-11 & 13 CCAFS OSTF-1, LC-576 & SLC-3, VAFB
Total launches	48
Successes	33
Failures	15
First flight	11 October 1960
Last flight	24 March 1995

The SM-65E Atlas, or Atlas-E, was an operational variant of the Atlas missile. It first flew on 11 October 1960, and was deployed as an operational ICBM from September 1961 until April 1966. Following retirement as an ICBM, the Atlas-E, along with the Atlas-F, was refurbished for orbital launches as the Atlas E/F.^[1] The last Atlas E/F launch was conducted on 24 March 1995, using a rocket which had originally been built as an Atlas-E.

As fully operational ICBMs, the Atlas E and F, which differed only in guidance systems, had upgraded engines and inertial control instead of the Atlas D's radio ground guidance. The ignition system was also different from the one used on the D-series, which used a "wet" start, meaning that the propellants were injected into the combustion chamber prior to ignition, and a hypergolic igniter on the fully developed version. The Atlas E/F for comparison used pyrotechnic cartridges and a dry start (ignition coming before propellant injection) for an extremely rapid ignition that required no hold-down time on the pad to prevent combustion instability. The booster engines had separate turbopumps unlike the Atlas D which had a common pump feeding all three main engines.

Atlas-E launches were conducted from Cape Canaveral Air Force Station, at Launch Complexes 11 and 13, and Vandenberg Air Force Base at OSTF-1, LC-576 and SLC-3.^[1]

The Atlas E testing program commenced on October 11, 1960 when Missile 3E was launched from Cape Canaveral's LC-13. All went well until booster jettison, at which point a malfunction of a staging disconnect valve caused loss of sustainer hydraulic pressure. The Atlas lost thrust, tumbled, and broke up at T+154 seconds. On November 30, the second attempt, Missile 4E, failed in almost identical fashion except that the missile remained structurally intact until impact in the ocean. Missile 8E on January 24, 1961 lost roll control due to aerodynamic heating shorting the vernier pitch control servo, a problem that had not occurred since the early Atlas A tests. Missile 9E on February 4 was successful. Missile 13E on March 14 experienced problems with the propellant utilization system and prematurely depleted its LOX supply. Missile 16E (March 25) experienced yet more valve problems, this time causing loss of pressure helium and made it impossible to jettison the booster section. The missile was dragged down by the weight of the spent booster engines and fell short of its intended range, also the propellant utilization system malfunctioned again and caused the engines to run fuel rich.

The repeated valve failures on the Atlas E were bewildering to Convair engineers, but Ed Hujsak, assistant chief engineer of mechanical and propulsion systems for the Atlas program, believed that the location of the propellant lines on the E/F missiles was causing LOX and RP-1 ejected from the spent booster engines following staging to mix and explode, possibly damaging valves. As evidence of this, he pointed to telemetry data from flights indicating a momentary pitching motion of the missile after booster jettison, which could be the result of the energy generated by exploding propellant. Hujsak proposed that additional cutoff valves be added to the propellant lines in the booster engines that would be closed just before jettison. This upgrade had to be retrofitted to missiles that had already been shipped, but Air Force officials argued that they only needed to add valves to the LOX lines on the grounds that the RP-1 could not detonate without oxidizer. Then on September 9, Missile 26E lost sustainer thrust following staging. Due to the momentary telemetry blackout during booster jettison, the exact cause of the failure could not be determined, but the gas generator was registering temperatures of over 1500°F. Vernier engine operation continued until 225 seconds into launch and the flight control system tried to correct the tumbling missile's flight path, but this was impossible with the loss of engine thrust. Impact in the Atlantic Ocean occurred about 500 miles downrange. After this debacle, the Air Force gave in and agreed to install cutoff valves. There were no more Atlas failures due to unexplained malfunctions at staging.

After two successful Atlas E flights in May, testing at Vandenberg AFB in California began. On June 7, an attempt to launch Missile 27E from OSTF-1 (a coffin silo) ended in an on-pad explosion when the vehicle suffered combustion instability in the B-2 engine that ruptured low pressure fuel ducting and started a thrust section fire, which quickly ignited the propellant tanks. The mishap, a near-repeat of two Atlas D failures the previous year, was attributed to the Atlas being released from the pad immediately on full thrust with no hold-down time to check for proper engine operation. This was followed by another failure at Cape Canaveral two weeks later when Missile 17E went out of control and destroyed itself 101 seconds after launch due to the gyroscope spin motor running at too low of a speed.

As the June 1961 accident had curtailed launches at Vandenberg until Complex OSFT-1 could be repaired, subsequent Atlas E flights during the year took place from Cape Canaveral and most of them were successful (as noted above, Missile 26E malfunctioned in-flight). But on November 10, an attempt to launch a biological mission (Missile 32E) with a squirrel monkey named Goliath ended in disaster as the Atlas's sustainer engine shut down almost immediately at liftoff, while the verniers failed to start at all. The booster engines managed to retain attitude control until a fire broke out in the thrust section and caused the B-1 engine to shut down at T+22 seconds followed by loss of electrical power and telemetry. The Atlas began tumbling uncontrollably and was destroyed by Range Safety at T+35 seconds, the B-2 engine continuing to operate until missile destruction. Goliath, who was in a padded container with no restraints, was recovered from the Atlantic Ocean three days later. A postmortem examination of the monkey found that he had died of multiple head injuries probably caused by impact with the ocean rather than separation of the capsule from the booster. Had the flight succeeded, Goliath would have been sent on a 5000-mile (8045 kilometer) suborbital lob and recovered in the South Atlantic. The capsule had no instrumentation or medical monitoring of the monkey, only a TV camera to record his actions during the flight. The sustainer engine was pulled from the ocean floor and examined, which found that a pressure transducer had accidentally been installed on the test port of the LOX regulator. This resulted in near-total LOX starvation of the sustainer engine. Fire in the thrust section was caused by RP-1 being ignited by the hot engine combustion chamber. The vernier engines never activated due to their startup timer being set to activate following sustainer start (which failed, thus preventing the start signal from being sent to the verniers). Despite these mishaps, the Atlas E was declared operational that month.^[2]

The failure of Atlas 32E caused momentary concern over Project Mercury, but NASA reassured the public that the flight used a different model of booster and that the improperly installed pressure transducer would not have occurred on the more tightly supervised Mercury program. Atlas E R&D flights concluded with Missile 40E on February 13, 1962 and the final operational test was Missile 71E on September 25, 1963.

The Atlas E and F were phased out of use as operational ICBMs in 1965 and replaced by the hypergolically-fueled Titan II. Decommissioned Atlas missiles were then used for military satellite launches from Vandenberg AFB well into the 1990s, sometimes with solid-fueled upper stages, sometimes not. These Atlases should be not be confused with the Atlas H which flew five times during the 1980s and was a standard Atlas SLV-3 (descendant of the original Atlas D) flown with solid upper stages.

During 1962-74, the Air Force conducted many dozens of test flights of reentry vehicles and Nike/Zeus target missiles. Most of these were on Atlas D or F missiles, however six of them used Atlas Es. No Atlas E launches took place between 1969 and 1979.

On December 9, 1980, Missile 68E was used to launch a NOSS ELINT satellite from VABF's SLC-3W. Shortly before staging, the B-1 engine shut down, causing the booster to perform a 180-degree loop and plummet back towards Earth, breaking up from aerodynamic loads as it descended. The failure was attributed to corrosion in a piece of ducting that resulted in loss of lubricant to the B-1 turbopump. The ducting in the Atlas could have been easily replaced, but the Air Force elected not to do so on the grounds that the space shuttle would be replacing expendable launch vehicles soon. In addition, the converted Atlas missiles still had various ICBM hardware features which were unnecessary for space launches and added more complexity and failure points. These included attachment ducts so that the lubricant oil tank could be mounted either horizontally or vertically during preparation for a silo launch. As a result of the postflight investigation for Atlas 68E, it was decided to inspect all existing launch vehicles for corroded plumbing and also remove unneeded ICBM hardware.

The last-ever failure of an Atlas caused by the booster itself, as opposed to the upper stages or other external factors, was an attempted launch of a military GPS satellite on December 19, 1981 using Missile 76E. The B-2 engine shut down seconds after liftoff, causing the Atlas to spin out of control and disintegrate. It then plowed into the ground leaving a burnt crater only a few hundred feet from Launch Complex SLC3E. Since no range safety action had been taken, the common bulkhead between the RP-1 and LOX tanks ruptured at impact, allowing the booster's nearly full fuel load to mix and turn into an explosive gel which detonated with the force of 20,000 pounds of TNT. Investigation of the booster debris quickly pinpointed the cause of the problem; a botched repair job on a metal O-ring that caused sealant to plug up ventilation holes in the gas generator, which overpressurized and ruptured shortly after ignition. Escaping flames then burned through a LOX feed line, cutting off the flow of oxidizer to the gas generator and causing B-2 engine shutdown.

The final Atlas E launch (Missile 45E launched on March 24, 1995) successfully carried a weather satellite aloft for the Air Force. A total of 64 Atlas Es were launched between 1960 and 1995, 30 of them being space launches. 16 launches failed.

See also

• SM-65 Atlas

References

1. Encyclopedia Astronautica - Atlas
2. https://docs.google.com/viewer?a=v&q=cache:l1YjtRZxeEMJ:www.dtic.mil/dtic/tr/fulltext/u2/843200.pdf+atlas+32e+launch+report&hl=en&gl=us&pid=bl&srcid=ADGEESg1Gx3UFypEA9BHybyEwN76n3FHG_TL4XTVoOkbYVDe3PHCcMrXzk8eUgIoGvzGw53LhU17qCF_LvcZdruGn5jTI0hqLgm6O3RtDf3FEVqSETVaGyScrw1wWoyD_K_rXdM8Vvdq&sig=AHIEtbQ9bNKDjcjqZzJCKVMZvuhe4Jh7RQ