Launch of an Atlas-E missile
Expendable launch system
|Country of origin||United States|
|Launch sites||LC-11 & 13 CCAFS
OSTF-1, LC-576 & SLC-3, VAFB
|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 gas generators unlike the Atlas D which had one gas generator for both engines.
The Atlas E testing program commenced on October 11, 1960 when Missile 3E was launched from Cape Canaveral's LC-13. At around 40 seconds into launch, the sustainer hydraulic system lost pressure. After booster jettison, the missile lost attitude control, tumbled, and broke up at T+154 seconds. On November 30, the second attempt, Missile 4E, repeated the same failure 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 making 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 failures on the first three Atlas E tests were traced to radiated heat, but malfunctions of random components on various flights following staging left Convair engineers flustered. 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, proposed after Missile 26E (September 9) suffered a gas generator failure following staging, 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. After an Atlas F in December lost sustainer hydraulic pressure following staging, the Air Force relented and agreed to install cutoff valves for the RP-1, and this failure mode did not repeat itself.
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 caused an explosion in the thrust section and subsequent complete destruction of the missile. 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. OSTF-1 was severely damaged by the explosion of 27E and would not be used again for seven months. 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 OSTF-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. Telemetry data became erratic at this point. 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. The nose cone impacted in the ocean about 20 seconds later. 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. Strong vibration in the gas generator from the shutdown ruptured low-pressure ducting and started a propellant leak that led to a thrust section fire. The vernier engines never activated due to their startup timer being set sustainer 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.
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 accident had no relevance to Mercury. Atlas E R&D flights concluded with Missile 62E on June 4, 1963 and the final operational test was Missile 71E on September 25, 1963.
Following the Cuban Missile Crisis in October 1962, several Congressmen voiced their concern about the reliability of the ICBM arsenal and whether it would actually work if called upon. Secretary of Defense Robert McNamara thus decided to carry out a test launch of an Atlas missile to verify its operability. The serial numbers of all currently deployed Atlas missiles were written down on pieces of paper, placed inside a hat, and one would be pulled at random. The winner turned out to be Missile 65E, then located at Walker Air Force Base in Kansas. This would be the first launch of an active duty ICBM from an operational silo facility, the Mk IV nuclear warhead would be replaced with a dummy unit and the guidance program changed to fire the Atlas into the Pacific Ocean instead of over the North Pole into the Soviet Union. However, the project quickly met with opposition from Kansas governor John Anderson as well as politicians from neighboring states who protested the idea of a missile flying over populated areas, especially since on-duty ICBMs lacked any Range Safety destruct system in the event of a malfunction. Even if the Atlas flew perfectly, the booster section would still have a high chance of landing in a populated area. Secretary McNamara eventually agreed to transport Atlas 65E to Vandenberg and have the Walker AFB crew launch it there.
Even with this change to a safer launching locale, Congress still argued over the geopolitical implications of such a test. A failure would damage US prestige, a success would send a needless provocation to the Soviet Union especially coming on the heels of the Cuban Missile Crisis. Atlas 65E was eventually launched on April 25, 1963 from OSTF-1 at Vandenberg, as a R&D flight carried out by a Convair team rather than the Walker missileers. The flight was completely successful and the Atlas flew 6000 miles downrange, missing the target point by only a few hundred yards.
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. The Range Safety destruct command was sent, resulting in a high-altitude explosion. 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 pitch over and nosedive into the ground. The Range Safety officer sent the destruct command moments before impact, leaving a burnt crater only a few hundred feet from Launch Complex SLC3E. 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, thirty of them being space launches. Sixteen launches failed.
- Encyclopedia Astronautica - Atlas