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FPS-24 Long range search Radar Set - A Long-range frequency diversity search Radar set designed for select SAGE System radar sites built by General Electric. Twelve units were built for the United States Air Force between 1958 and 1962 by General Electric.

Malmstrom AFB FPS-24 Radar Site (center) circa 1964-1971.

These radar sets, like the FPS-35, 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 eight of the FPS-24 installations with the other four installations using steel framed towers. The rotating antennas were very large and only two were covered with a radome, Mount Hebo Air Force Station and Cottonwood Air Force Station.

FPS-24 Radar Set Locations (edit list)
Site State Unit SAGE From To GPS Type Twr Status Rev Notes
Eufaula AL 609th Z-119 1959 1968 31.8814,
Steel Gone * Prototype
Bearing failure 1968
closed the site
Point Arena CA 776th Z-37 1961 1976 38.8886,
Concrete Exists 1st production unit
Almaden CA 682nd Z-96 1962 1980 37.1605,
Concrete Exists 2nd production unit
Designated historic
Cottonwood ID 822nd Z150 1962 1964 46.0667,
Steel Exists * Bearing failure 1964
closed the site early
Bucks Harbor ME 907th Z-110 1963 1979 44.6294,
Concrete Gone *
Port Austin MI 754th Z-61 1962 1982 44.0303,
Concrete Exists Bearing failure 1982
FPS-24 replaced by FPS-91A
Baudette MN 692nd Z-132 1962 1979 48.6707,
Concrete Exists
Malmstrom MT 801st Z-147 1964 1970? 47.5018,
Steel Gone *
Winston-Salem NC 810th Z-130 1962 1970 36.0435,
Concrete Exists
Mount Hebo OR 689th Z-100 1962 1969 45.2158,
Steel Gone *
Oakdale PA 662nd Z-62 1963 1969 40.3991,
Concrete Exists
Blaine WA 757th Z-46 1963 1979 48.9119,
Concrete Exists *
FPS-24 Bearing Lives Table.
FPS-24 on Open Steel Tower.

The initial installations of the FPS-24 revealed many problems that caused a delay in operational status. The problems were resolved and the radar was operational in 1962. The antenna system provided another set of operational problems mostly due to failures of the bearing that the 85.5-ton antenna rotated upon. Catastrophic bearing failures sometimes caused secondary damage to the support towers, sails, and feed horns. Some sites were actually closed due to catastrophic failure of the antenna system and others were forced to install other search radar sets when the damage could not be repaired. At Mount Hebo Air Force Station fears that the high winds would damage the FPS-24 antenna led to three attempts to enclose it in a radome. All three radomes were destroyed by the high winds and the last radome failure also damaged the antenna sail. The FPS-24 was removed and replaced with a FPS-27.

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 bearing problem was the development of a hydrostatic bearing for the AN/FPS-24 by Goodyear Aerospace Corp. The prototype was tested at Oakdale Air Force Station. The test was terminated after 7821 hours with a catastrophic failure caused by human error. That bearing is shown on the chart above in line 9. That FPS-24 was not supplied with another bearing and it shut down in 1969. No other sites had received the hydrostatic bearings as of the date of this report (1970) and some 40 bearings had been replaced.

Current Status

All of the radar sets have now been dismantled and removed from the buildings and although many of the towers remain there are no antennas still installed.

FPS-24 Search Radar

FPS-24 Search Radar
Element Value Notes
Nomenclature FPS-24
Manufacturer General Electric
Type Search
Number Made 12
Frequency 214 to 236 MHz
PRF 278
Pulse Width 20 us
Power 7.5 mw max
5 mw normal
Range 250 nmi Long range
Rotation Speed 5 rpm
Reflector Width 120'
Reflector Height 44'
Rotating Weight 178,000 lbs
218,000lbs with ice
Bearing Type 4 point Contact Ball & Crossed Roller
Bearing Pitch Diameter 10'
Number of Balls 84
Number of Rollers 116
Ball Diameter 3.5"
Roller Diameter 2.68"
Introduced 1961
Blaine AFS Concrete FPS-24 Tower.
Cottonwood AFS Enclosed Steel FPS-24 Tower.

See Also:


  • Winkler, David F., Searching the Skies: the Legacy of the United States Cold War Defense Radar Program, USAF Hq Air Combat Command, 1997, 192 pages, Pdf
  • RADC-TR-71-81 Technical Report December 1971, Bearing Improvement Program For Large Rolling Element Bearings, Pdf


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