1. EECS-823 System Presentation
The AN/FPS-85
EECS-823 System Presentation

2. AN/FPS-85: Army-Navy Fixed Position Search Radar
A 32 MW phased array radar located at Eglin Air Force Base in Florida operated by the 20th Space Control Squadron
One of 29 sensors in Space Surveillance Network used to track both manmade and not-manmade objects in space.
Records around 16 million observation events per year, around 30 observations per minute, capable of keeping track of 200 objects over short time interval.
Operating range exceeds 40,000 km, around 1/10th the distance to the moon
As originally built, could detect 1m^2 target at 7,500 km from a single pulse
With upgrades, capable of detecting and tracking objects smaller than 5 cm^2 in LEO (~1,700km), and objects around 1m^2 in GEO (~35,000km)

3. History
Developed in response to the existence of Fractional Orbital Bombardment System (FOBS)
Launched into arbitrary LEO as opposed to directed ICBM
Resulting from a feasibility contract with Bendix, construction started in 1962 and was scheduled for a 1965 completion
Partially Destroyed in 1965 in electrical fire, four months before completion
Became operational in 1969 with a primary mission of tracking satellites and objects in low earth orbit
In 1975 it was refocused to target shorter range ballistic missiles
In 1987 it was returned to space surveillance, replaced by the PAVE PAWS system (Precision Acquisition Vehicle Entry Phased Array Warning System)
In 1988 an upgrade was made to enable deep space observations (pulse integration)

4. The building in 1963

5. Physical Dimensions
318 ft long, 143 ft high 250k sq ft base 2.5 M cubic ft structure

6. Transmit Antenna Setup
5928 individual elements fed by 5184 transmit modules
72 ft x 72 ft square array
Elements are shortened dipoles with a parasitic director
Element spacing around 0.55λ
Usually uniform power distribution
Beamwidth of around 1.4 deg.
Physical angle of 45 deg
Azimuth beam range of 120 deg
Elevation beam range of 3 deg to 105

7. Receive Antenna Setup
192 ft Square grid array with element distribution tapered octagonally
4,660 receive modules fed by 19,500 receive elements
Elements are crossed dipoles
Has interesting pattern of a 3x3 lobe cluster, each lobe 0.4 deg in width, total Beff of 1.6 deg.
Steering accomplished with 7 bit row and column phase registers

8. Transmitter Operation
The radar operates at a center frequency of 442 MHz, with a maximum bandwidth of 10 MHz
Transmit antenna is fed by 5184 UHF modules, each with a tetrode capable of 10 kW pulses for 250 us.
The modules are fed by 16 banks of pulse modulators, or oscillator distribution driver.
Switches between 1, 5, 10, 25, 125, 250 us pulse durations depending on operating mode.
10 kW to 175 kW average total operating power

9. Original Waveform Configuration
With a normal detection PRF of 20 Hz, each resource period involves multiple pulses

10. Control and Processing
Control and processing originally accomplished with two IBM System/360 mainframes
Has since been upgraded to use two IBM System/390 mainframes along with a newer set of SPARC workstations.
The defined fence can be changed dynamically as the radar switches operating modes.

11. Pegasus Breakup

12. Operational Considerations
As built it relies on vacuum tubes, which fail regularly (several per day)
Six active staff members help maintain and operate the station.
SwRI is currently handling maintenance improvements and is working on upgrades.
Power is supplied commercially, relies on 2x 250 KVA UPS to handle shortages along with three 500 KW diesel generators.
Three water pumps, 1500 gallons per minute each, 500,000 gallons of storage for cooling
A now inactive firehouse is present in the complex.
Estimated around $2 million in annual operating costs.

13. Citations https://www.globalsecurity.org/space/systems/an-fps-85.htm
The AN/FPS-85 Radar System; J. Reed, Proceedings of the IEEE, Vol. 57, No. 3, March 1969
An Eglin Fence for the Detection of Low Inclination/High Eccentricity Satellites; W. Burnham, R. Sridharan, Proceedings of the 1996 Space Surveillance Workshop, p45, (April 1996)
A Fragmentation Event Detection System; G. Zollinger, R. Shridharan, Acta Astronautica Vol. 46, No. 7, p477, (March 1999)
Report on Space Surveillance, Asteroids and Commets, and Space Debris Vol3; USAF SAB