AN/FPQ-6

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The AN/FPQ-6 is a fixed, land-based C-band radar system used for long-range, small-target tracking. The AN/FPQ-6 Instrumentation Radar located at the NASA Kennedy Space Center was the principal C-Band tracking radar system for Apollo program.

RCA’s Missile and Surface Radar Division developed the FPQ-6 skin tracking C-Band radar as a successor to the AN/FPS-16 radar set. The AN/FPQ-6 can provide continuous spherical coordinate information at ranges of 32,000 nautical miles (59,264 kilometers) with an accuracy of plus and minus 6 ft (1.8 m). The AN/FPS-16 has range limited to 500 nmi (926 kilometers) with an accuracy of 15 feet (4.57 m), although it could be modified to a maximum range of 5,000 nmi (9260 kilometers).


Radar Ground Station Characteristics
------------------------------------

                           AN/FPS-16       AN/FPQ-6
                           ---------      ---------
Frequency band (MHz) . .   5400-5900      5400-5900
Peak power (mW) ......        1.3            3.0
Antenna size (m) ........    3.9            9.2
Antenna gain (dB) ......       47             52
Receiver noise figure (dB)    6.5              8
Angle precision (units) . . . 0.15           0.1
Range precision (m)......    4.5            3.0

The AN/FPQ-6 radar employed a 2.8 megawatt peak power (4.8 kilowatt average), broad banded (5400 – 5900 MHz) transmitter with a frequency stability of 1 x 10⁸.

The 8.8 meter diameter parabolic antenna, using a Cassegrain antenna feed, had a 0.4° beamwidth and a gain of 51 dB. Its monopulse, 5 horn feed system permitted the reference and error antenna patterns to have their gains independently established as well as the slope of the error patterns optimised while supplying target return signals to the receiving system with a minimum of insertion loss.

The three channel signal outputs of the antenna feed system were supplied directly to the receiving system without undergoing any additional loss-inducing signal manipulation with bandwidths optimised for the specified pulse widths of 0.5, 0.75, 1.0 and 2.4 microseconds and the receiver noise figure of 7.5 dB was improved to 3.5 dB through the addition of closed-cycle parametric RF amplifiers. This system ensured a dynamic range in excess of 120 dB.

The receiving system provided simultaneous presentation of the skin and beacon returns to the console operator so that skin tracking could be used if the beacon signal was lost.

The antenna pedestal was a high precision, two axis mount, using a hydrostatic bearing in azimuth and phase roller bearings in elevation to provide mobility and support to the counterbalanced, solid surface antenna. The antenna was positioned through anti-backlash dual drive pedestal gearing via a high torque-to-inertia electro-hydraulic valve motor system. A viscous coupler located between the valve motor and pedestal drive gearing damped out undesired mechanical resonances.

The AN/FPQ-6 had a self contained digital computer, an RCA FC-4101, whose primary purpose was to correct dynamic lag in the angular output data. As designed, both the AN/FPQ-6 and AN/TPQ-l8 radars were provided with a built-in data processor referred to as the RCA 4101 Computer.

The ground floor of the two story building contained the air-conditioning, transmitter heat exchanger controls, equipment load center data input junction box and ex-Mercury atomic time standard The first floor contained the 8 equipment racks, the console, and the 3 megawatt transmitter.

[edit] Functional Description

The AN/FPQ-6 Missile Range Instrumentation Set is a fixed station long-range precision tracking set to be used for tracking intercontinental ballistic missiles for range safety and range user's trajectory measurement data. It will also be used for tracking during staging and parking orbit (trilateration) of a synchronous satellite, The operational objective is to provide a fixed station radar capable of skin tracking a square meter target to ranges in excess of 300 nmi (560 km).

The specifications for the FPQ-6 radar installation at Patrick Air Force Base, Florida, are shown in the following table.

Apollo Land-Based C-Band Radar Characteristics


Station    Station        Radar     Antenna      Peak    Receiver   Receiver    Unambiguous
           Location       Type     Diam.  Gain   Power    Noise    Bandwidth      Range
                                   (ft)   (dB)  (MW)  Figure     (MHz)      capability
                                                          (dB)                  (nmi)
-------------------------------------------------------------------------------------------
PAFB    Patrick Air       FPQ-6     29     51      3        4          1.6       32,000
        Force Base, FL

NOTE:
The nominal frequency range is 5.4 to 5.9 GHz.
Receiver bandwidth is for 1 microsecond pulsewidth.
FPS-6 radars have circular polarization capability.