The SM-65E Atlas, or Atlas-E, was an operational variant of the Atlas missile. It first flew on October 11, 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 March 24, 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 launcher system used for the E and F series was also different from the D series, eliminating the hold-down arms in favor of a mechanism that would immediately release the missile as thrust built up.
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.
1960–61 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. Both of these failures were traced to radiated heat that caused a failure of the sustainer hydraulic rise-off disconnect, which ruptured and allowed the hydraulic fluid to escape; they resulted in shielding being added to protect the rise-off disconnect."Flight Test Evaluation Report, Missile 4E Convair December 14, 1960"
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 experienced problems with the propellant utilization system and prematurely depleted its fuel supply, however the warhead landed only a few miles short of the target, so the flight was considered a success. Missile 13E (March 14) experienced a similar problem, but with a much earlier sustainer cutoff and the warhead missed its target by almost . Missile 16E (March 25) depleted its supply of helium control gas early, 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 failure was traced to two mistakenly transposed wires which caused spurious venting of the control helium out the vernier engines."Flight Test Evaluation Report, Missile 16E Convair April 8, 1961"
Missile 12E (May 13) and Missile 18E (May 26) both performed well. Testing now began at VAFB on the West Coast, but the first attempt ended ignominiously when Missile 27E lifted from OSTF-1 (Operational Silo Test Facility) on June 7. The B-1 engine almost immediately shut down at liftoff due to rough combustion, causing a fire in the thrust section that led to the explosion of the missile only four seconds after launch. The failure, a near-repeat of two Atlas D accidents the previous year, extensively damaged OSTF-1 and put it out of use for months. Postflight examination of the missile hardware found extensive damage to the B-1 engine injector head. Afterwards, copper baffles were installed in all injector heads and the engine start sequence changed to wet start (an inert fluid kept in the engine tubes to reduce shock at ignition). The downside of this was adding of additional weight as well as slightly reduced engine performance. The ARMA guidance system on 27E also experienced erratic behavior due to an intermittently shorted diode; the guidance system had flagged a "No-Go" signal during an abortive launch attempt of 27E two days earlier and a rerouting wire was installed around a switch. Had the flight continued, it's possible that the missile would not have achieved a proper trajectory."Flight Test Evaluation Report, Missile 27E Convair June 21, 1961"
The next Atlas E test, from Cape Canaveral, was also a spectacular failure. Missile 17E on June 23 experienced a malfunction of the pitch gyro motor, which was apparently running at 84% speed. The missile began to oscillate in the pitch plane starting at T+15 seconds. At T+79 seconds the LOX tank pressure increased from aerodynamic heating or propellant slosh and at T+97 seconds aerodynamic loads from the excessive pitch rate caused collapse of the vernier fairing, rupturing a low pressure hydraulic line and causing loss of hydraulic pressure to the sustainer and verniers. The missile broke up three seconds later from either aerodynamic heating or structural loads. After this debacle, all remaining Atlas E/F R&D flights had the SMRD (Spin Motor Rotation Detector) system installed."Flight Test Evaluation Report, Missile 17E Convair July 7, 1961"
Atlas E tests at VAFB were curtailed until OSTF-1 could be repaired, and for the remainder of 1961 all testing took place from the Cape. Following two successive flights ending in explosions and an incinerated launch stand, the successful flights of Missiles 22E and 21E during July, followed by the first Atlas F flight in August, came as a relief. On September 9, Missile 26E lost sustainer thrust following BECO and tumbled, falling into the Atlantic Ocean almost short of its target. Two E-series flights in October, 25E and 30E, were both successful.
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 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 due to an erroneous schematic diagram of the sustainer hardware. 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 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.
The sustainer malfunction on Missile 26E had been traced to a gas generator failure which occurred during the staging sequence, but the exact reason for it was unclear, in part because of the normal momentary telemetry blackout that occurred at booster jettison due to ionized engine exhaust gases impinging on the telemetry antenna. When telemetry returned, the sustainer gas generator temperature was over , suggesting a LOX-rich shutdown."Flight Test Evaluation Report, Missile 26E Convair September 23, 1961"
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 or plumbing. 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. The conclusion was that such an event had ruptured low pressure ducting on Missile 26E and caused loss of fuel flow to the sustainer gas generator, or else propellant residue had obstructed the ducting. 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.
On December 6, Missile 6F suffered a leak in the sustainer hydraulic system at BECO, resulting in eventual loss of hydraulic pressure and failure to achieve the planned range. After this debacle, the Air Force relented and agreed to install cutoff valves for the RP-1 lines as well, and this failure mode did not repeat itself.
1962 The final Atlas E test from CCAS was Missile 40E on February 13, 1962. With OSTF-1 back in operation, Missile 66E launched on March 1. Shortly after liftoff, a thrust section fire started in the vicinity of the fuel fill/drain valve. It continued until approximately T+50 seconds and then disappeared, but apparently resulted in damage to the thrust section, as the helium control gas leaked and resulted in vernier engine shutdown as well as no booster jettison. After BECO, the sustainer engine was left dragging the dead weight of the booster section. This combined with the loss of roll control from vernier shutdown caused the missile to tumble and finally break up at T+295 seconds. The exact reason for the thrust section fire was not determined. In addition, an erroneous signal from a pad umbilical threw open the LOX boil-off valve at liftoff, causing a gradual decay in tank pressure during ascent, although this was a secondary failure that did not contribute to the eventual loss of the missile."Flight Test Evaluation Report, Missile 66E Convair March 14, 1962"