Ellsworth Air Force Station
Ellsworth Air Force Station (1954-1962) - A Cold War U.S. Air Force Radar Station established in 1954. Located on Ellsworth Air Force Base in Jackson County, South Dakota. Initially assigned a Permanent ID of M-97. Closed in 1962.
Established late in 1954 and became operational in 1955 as the Ellsworth Air Force Base Radar Site manned by the 740th Aircraft Control & Warning (AC&W) Squadron.
Initial equipment included the MPS-7 search radar and a MPS-14 height-finder radar. In 1959 a FPS-20A search radar replaced the MPS-7 set. This configuration (a SAGE qualified long range search radar and two SAGE qualified height-finders) met the requirements for transition to SAGE System operation.
SAGE System Transition
The transition of the manual GCI system to the automated SAGE system began with the installation of the FST-2 coordinate data transmitter and search radar upgrades. The FST-2 equipment digitized the radar returns and transmitted the digital returns to the SAGE direction center. Under the SAGE System, interceptor aircraft were directed to their targets by the direction center computers and controllers, greatly reducing the need for local controllers and equipment at every radar station.
The FST-2 was a very large digital system using vacuum tube technology. Over 6900 vacuum tubes were used in each FST-2 requiring 21 air-conditioned cabinets, 40 tons of air conditioning, 43.5 kva of prime power and usually a large new addition to the operations building. The FST-2B modification added two more cabinets but with newer solid state (transistor) technology to process coded responses from aircraft transponders.
SAGE System Operation
Period pictures appear to show the FPS-20 tower and the SAGE Annex simultaneously under construction but it is not clear if the SAGE Annex was completed or if FST-2 was installed and became operational. The site did come under the control of Minot ADS, feeding data to the Minot SAGE Direction Center DC-19 but it is unclear if this was in the manual mode or the automated mode using the FST-2.
The public announcement of the site closure came in December 1961 indicating that coverage would be assumed by Sundance Air Force Station. The Ellsworth radar site and the 740th were deactivated on 15 Aug 1962.