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. 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.

The Atlas E testing program commenced on October 11, 1960 when Missile 3E was launched from Cape Canaveral's LC-13. It and the second test (Missile 4E) on November 30 both failed due to loss of sustainer engine hydraulic pressure at around one minute into the flights due to valve malfunctions during booster staging. Missile 8E on January 24, 1961 was lost due to an electrical short that disabled the vernier engines. The fourth attempt on February 24 was successful. Another electrical glitch occurred in the fifth Atlas E launch on March 14 which led to premature fuel depletion. The sixth attempt (March 25) failed to stage its booster section because of a valve problem.

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. However, after Missile 26E (September 9, 1961) lost sustainer engine thrust following staging, it was decided that the RP-1 cutoff valves were necessary after all. Following the fix, no more Atlases were lost to unexplained valve problems.

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 a coffin silo failed when the vehicle suffered combustion instability in the B-2 engine which caused the missile to tip over at launcher release and explode on impact with the silo wall, putting the facility out of commission for six months. The mishap 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 due to the gyroscope spin motor operating at an incorrect 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 in November, an attempt to launch a biological mission (Missile 32E) with a squirrel monkey named Goliath ended in disaster as the Atlas's sustainer engine and verniers shut down almost immediately at liftoff. The booster engines managed to retain attitude control until a fire broke out in the engine compartment and caused the right booster engine to shut down at T+22 seconds (the left engine continued to operate until missile destruction) followed by loss of electrical power and telemetry. The Atlas began tumbling uncontrollably and was destroyed by Range Safety at T+35 seconds. 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 accident was found to be the result of an improperly installed pressure transducer that prevented the sustainer LOX regulator from working. Despite these mishaps, the Atlas E was declared operational that month.

There were still unforeseen design flaws and failure modes to be overcome, such as Missile 64E in December 1962 which suffered a turbopump failure and loss of B-2 engine thrust around 60 seconds into launch, causing the vehicle to pitch down and break up from aerodynamic loads. This incident was traced to a pressure bubble in the engines at liftoff that jammed an insulation blanket onto a vent valve for the turbopump lubricant tank, pulling it open and allowing the lubricating oil to leak out. The B-2 turbopump then shut down due to the loss of lubricant. To prevent a recurrence of this scenario, a different coolant was used in the Atlas's engines to produce a smoother startup and reduce the risk of pressure bubbles forming.

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.

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