FPS-35

 long-range fixed search radar set - A long-range Frequency-diversity search radar designed for select SAGE System radar sites. Twelve units built for the United States Air Force by Sperry Gyroscope. These radar sets were installed in and on five-story towers that were each capped with a 70 to 80-ton rotating antenna. Two types of towers were used, the most common was a five-story concrete tower that rose 84' 6" high with a 60' 3" square footprint. This configuration was used in ten of the installations with the other two installations using steel framed towers. The rotating antennas were very large and only one, Baker Air Force Station, Oregon was covered with a radome. The Baker Air Force Station FPS-35 radome was mounted on a separate Radome Support Structure (RSS) that surrounded the tower.

The initial installations of the FPS-35 revealed problems that caused some of the sites to delay operational status until 1962. The Montauk AFS installation caused radio interference problems in the vicinity and that radar was taken out of service in 1961. The problems were resolved and the radar was operational in 1962. The antenna system provided another set of problems, one of the worst being the catastrophic failure of the antenna system at Fortuna Air Force Station in 1966 where the antenna folded down over the building. That failure was attributed to a shear pin failure.

From the RADC-TR-71-81 Technical Report December 1971, Bearing Improvement Program For Large Rolling Element Bearings: AN/FPS-24 and ÄN/FPS-35 Air Defense Radars were designed for continuous, highly reliable operation in the SAGE (Semi-Automatic Ground Environment) system. It was intended that these radars should operate 365 days a year, 23 hours a day, for ten years, one hour a day being allowed for preventive maintenance. However, it soon became apparent that this degree of reliability was not to be realized. Azimuth bearings began to fail at an average rate of once a year on each AN/FPS-24, and once every two years on each AN/FPS-35. Because this high failure rate was not anticipated, ease of replacement had not been given major consideration in the design. Consequently, bearing changes required radars to be shut down for as long as three months, with costs as high as $ 175,000 for a single bearing change. This situation was intolerable to the user, Aerospace Defense Command (ADC), and to the Air Force Logistics Command (AFLC), which was responsible for supplying replacement bearings. As a result, direction was received to take immediate action to alleviate the urgent problems of supply and replacement time and to undertake concurrently a long-range program of general improvement in the large antenna bearing area.

RADC-TR-71-81 Technical Report December 1971, Bearing Improvement Program For Large Rolling Element Bearings, Pdf

The cure for the FPS-35 bearing problem was a combination of a change of bearing types and changes in lubricant. Those changes made an improvement in bearing life but did not result in bearings that met the 10 year life span.

Current Status
All of the radar sets have now been dismantled and removed from the buildings except for the one at the former Montauk Air Force Station (Now Camp Hero State Park) on the eastern tip of Long Island, New York. That structure was listed on the National Register of Historic Places in 2002 and has the antenna still mounted, now rusted and non-rotating. The building may also contain some of the radar set equipment and cabinets but is currently not open to the public.

FPS-35 Search Radar
See Also:
 * FPS-24
 * Fortuna Air Force Station
 * Finley Air Force Station
 * Montauk Air Force Station
 * US Radar Sets
 * Permanent System Radar Sites

Sources:
 * , page 39, 80.
 * RADC-TR-71-81 Technical Report December 1971, Bearing Improvement Program For Large Rolling Element Bearings, Pdf

Links:
 * Radomes - FPS-35
 * Wikipedia - FPS-35
 * Radomes - Fortuna AFS FPS-35 Antenna Collapse]