ATHENA computer

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"The Athena Missile Guidance Computer was designed by Seymour Cray at Sperry Rand Corporation. It was designed to guide the silo-launched Titan-1 missile.

The Athena cost about $1,800,000. when new, and weighed over 18,000 lbs. It spent most of its operational life in a missile silo.

The computer, when declared surplus by the Federal Government, went to various US universities. The one at Carnegie was used as an undergrad project until 1971, when the former EE undergrad students (Athena Systems Development Group) orchestrated its donation to the Smithsonian. It joined a sister unit, the Atlas Mod I Guidance Computer, at the Smithsonian.

The architecture was Harvard; separate data and instruction memories were used.

A Frieden terminal with paper tape equipment was used with the Athena, as well as an operating console. An interesting feature is the mode "BattleShort". In this mode, referred to as melt-before-fail, the power to the machine could NOT be shut off.

The Athena used a massive motor-generator set with 440 volt 3 phase AC input. I hooked this up from the lab mains, and got the generator set going initially. When the generator was started, the building lights dimmed, and there was no question that the machine was on. The motor generator control unit (seen behind the console) weighed a ton, and the motor/generator itself weighed over 2 tons.

The last launch supported by an Athena computer was a Thor-Agena missile launched in 1972 from Vandenberg AFB in California. It was used on over 400 missile flights. In its operational life, it never launched a missile in anger. The 18 Titan-1 Missile Complexes were only a stop-gap measure (awaiting the Minuteman Missile) and none of the complexes were operational for more than four years."

-- Unisys History Newsletter Volume 3, Number 4 August 1999 Sperry Rand Military Computers 1957-1975 by George Gray

Although many of the computers of the 1940s were developed as military projects, the use of vacuum tubes made them too big and unreliable for incorporation into actual weapons systems. The Eckert-Mauchly Computer Corporation built the BINAC in 1949 for Northrop Aircraft, but no one seriously expected it to be put into an airplane. The massive SAGE (semi-automatic ground environment) system built by IBM during the 1950s for the North American air defense system was for command and control, not for missile guidance. When vacuum tubes were replaced by transistors, it became possible to have computers of smaller size and greater reliability. The transistor was invented at Bell Laboratories in 1948, but it took several years of development to become suitable for use in computers. Bell Labs built the first transistor computer, the TRADIC (Transistor Digital Computer), for the Air Force in 1954. It used 700 point-contact transistors and 10,000 germanium diodes. (A diode is an electronic device which allows current to flow in only one direction.) Both of the two major computer development groups (St. Paul and Philadelphia) at Sperry Rand became involved in early transistor computer projects. Philadelphia became embroiled in the long and costly LARC supercomputer project for the Atomic Energy Commission. St. Paul, building on its early work for the Navy, became heavily involved in military projects.

[edit] Athena

St. Paul made its first venture into transistors with the Athena ground guidance computer for the Air Force's Titan intercontinental ballistic missile (ICBM). A ground guidance computer, as the name indicates, stayed on the ground and transmitted instructions to the missile. The Athena's designers had a choice of technologies. During the early 1950s there was a period of time when the magnetic amplifier, which was eventually used in the UNIVAC Solid State computer, was a serious rival to the transistor. One of the first proposed designs of the Philadelphia division's LARC computer used amplifiers, but they were soon rejected as being too slow for a machine which had to be very fast. At St. Paul, the lead computer designer for the Athena project, Seymour Cray, directed the construction of two prototypes. The Magnetic Switch Test Computer (MAGTEC) used magnetic cores, while the Transistor Test Computer (TRANSTEC) used transistors. They had identical instruction sets. Two versions of the MAGTEC were built; both had magnetic core circuits on plug-in cards less than three inches square which were mounted on racks. There were two models of the TRANSTEC, which had transistor circuits on its plug-in cards. The TRANSTEC II had 4,096 24-bit words of memory. After thorough testing, Cray was satisfied that transistors were superior and would be reliable enough to meet the stringent requirements in the Athena contract.

The Athena computer had 256 words of 24-bit core memory to be used as a data work area and an 8192-word drum for the storage of the program and data items which did not change (constants). The Athena was completed in 1957. It occupied 370 square feet and weighed 21,000 pounds. Once in service, it was found to have a mean time to failure of 48 days, twenty times better than the original specifications. Since the late 1950s were the time of the perceived "missile gap" between the U.S. and the Soviet Union, the U.S. Air Force deployed the liquid fuel Titan as an interim measure pending the completion of the solid fuel Minuteman ICBM. St. Paul delivered 23 Athena computers to Air Force sites by the mid-1960s. In the late 1960s, the Air Force gave one of the original Athena computers to the electrical engineering department of Carnegie Mellon University. It was used for various class projects and later donated to the Smithsonian Institution