SM-65F Atlas

Atlas-F (SM-65F)

Launch of an Atlas-F missile
Function	ICBM Expendable launch system
Manufacturer	Convair
Country of origin	United States
Launch history
Status	Retired
Launch sites	LC-11 & 13 CCAFS OSTF-2, LC-576 & SLC-3, VAFB
Total launches	70
Successes	53
Failures	17
First flight	8 August 1961
Last flight	23 June 1981

The SM-65F Atlas, or Atlas-F, was the final operational variant of the Atlas missile, only differing from the Atlas E in the guidance package. It first flew on 8 August 1961, and was deployed as an operational ICBM between 1961 and 1966. Following retirement as an ICBM, the Atlas-F, along with the Atlas-E, was refurbished for orbital launches as the Atlas E/F.

Most refurbished Atlas F space launches used solid-fueled upper stages, a notable exception being Missile 23F which launched Seasat, a military oceanography satellite, on June 27, 1978 using the last-ever Agena stage flown. The final Atlas F launch took place on June 23, 1981 when Missile 87F successfully placed a NOAA weather satellite into orbit.

The first two Atlas F flights from Cape Canaveral in August and November 1961 were successful and the third on December 12 mostly successful. On the 21st, Atlas 6F lifted off of LC-11 carrying a rhesus monkey named Scatback. This was the third launch of a primate on an Atlas in the past month - the first was Mercury-Atlas 5 which successfully lofted a chimpanzee on a three-orbit mission while the second, an Atlas E test, malfunctioned shortly after liftoff and had to be destroyed, claiming the life of the squirrel monkey it was carrying. Atlas 6F performed otherwise acceptably, but the sustainer engine shut down prematurely and it did not achieve its planned range. The capsule separated and splashed down near Ascension Island in the South Atlantic, however the tracking beacon failed to operate and recovery crews could not locate it. They gave up the search and Scatback was officially lost at sea.

So far, the Atlas F test program had gone well and nobody was prepared for the upcoming disaster on April 9, 1962 when Missile 11F exploded only one second after liftoff from LC-11. Subsequent investigation found that the sustainer LOX turbopump exploded due to the impeller blades rubbing against the metal casing and causing a spark that ignited the LOX. Testing now began at Vandenberg AFB and Missile 15F flew successfully on August 1. Atlas 57F on the 10th was another loss, this time due to a guidance failure at T+57 seconds that necessitated destruction of the vehicle by Range Safety. The next test launch took place from the now-repaired LC-11 at the Cape two days later and all subsequent R&D flights went without a hitch except for 13F in November which suffered premature engine shutdown due to overheating. After the flight of Atlas 21F in December, the vehicle was declared operational.

Operational tests of the Atlas F were mostly successful, but two flights from Vandenberg (Atlas 45F in October 1963 and Atlas 3F in April 1964) suffered stuck engine valves and fell back onto the pad at liftoff. In 1965, the Atlas was retired from service as an ICBM and remaining missiles used for suborbital and orbital launches over the next few decades. There were two major failures during the 20 years as a satellite launcher. One was an attempted launch of an unknown military test payload in April 1975 when a glob of LOX/kerosene gel fell into the flame pit at ignition, exploded, and damaged the Atlas's sustainer engine. The launch vehicle continued to operate for over two minutes, but the sustainer and verniers eventually shut down and the range safety destruct command was issued at T+303 seconds. Since the LOX gel explosion also damaged wiring in the base of the booster, the telemetry system lost power and no data was returned during launch, making it difficult to determine the exact cause of the engine failure. It was thought that damage to a piece of plumbing was the most likely explanation.

The other was a launch of a NOAA weather satellite on May 29, 1980. Performance appeared normal until booster jettison when the trajectory was discovered to be off-course. The sustainer engine kept burning long past its normal cutoff time, up to 50 seconds. When the satellite finally separated, it was inserted into a useless elliptical orbit.

The failure was caused by a seal jostled loose by the rapid-fire pyrotechnic cartridge ignition system used in the Atlas E/F missiles, flooding the B-1 turbopump with fuel and slowing down its rotation speed, cutting thrust levels in the engine to 80% and considerably reducing booster velocity and fuel consumption. The Atlas's onboard computer tried to compensate first by extending the booster engine burn time, but eventually a backup command forced booster shutdown and jettison. After BECO, the computer still tried to compensate by extending sustainer burn time until it went nearly a minute past what would have been normal cutoff. Following SECO, the booster also had to execute vernier solo mode for another 11 seconds. However, for simplicity reasons, the NOAA satellite had no electrical interface with the Atlas and so its solid rocket kick motor activated at a preset separation time. The Atlas was consequently still running when this happened, causing the kick motor to rupture the LOX tank dome, which registered on telemetry readouts as an immediate loss of tank pressure. As a result, the satellite reached a useless orbit and had to be abandoned.

Atlas F launches were conducted from Cape Canaveral Air Force Station, at Launch Complexes 11 and 13, and Vandenberg Air Force Base at OSTF-2, LC-576 and SLC-3. A total of 55 Atlas F missile tests were conducted between 1961 and 1974, the post-1965 launches all being tests of reentry vehicles as Atlas had been retired from ICBM service, along with 39 space launches during 1967 to 1981. There were 16 failures.

See also

• SM-65 Atlas