Apollo/Advanced Range Instrumentation Aircraft

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Antenna Control

    The antenna feed is a monopulse type, instantaneous phase comparison, tracking arrangement with separate elements for VHF and S-band. The VHF elements can be configured during pre-mission setup, before a flight, to provide either horizontal and vertical or right and left circular polarization sensing. The antenna operator manually acquires the target by positioning the 83-inch parabolic antenna, mounted on the front of the aircraft, towards the projected vehicle coordinates. Depending on the signal strength, the antenna can automatically track a target in VHF or S-band. However, when both bands are received simultaneously, the S-band track will typically be used.

The primary electrical characteristics of the antenna and feed are as follows:

1. Antenna Beamwidth:
    VHF, approximately 40 degrees. UHF, S-band, 4.7 degrees.

2. Antenna Gain:
    VHF 12 dbm minimum. UHF, S-band, 29 dbm minimum.

3. Feed:
    Two-channel monopulse for both UHF, S-band, and VHF.

4. Frequencies of operation:
    225 to 315 MHz.
    1435 to 1540 MHz.
    2200 to 2300 MHz.

5. Feed polarization:
    VHF Pre-mission selection of vertical and horizontal polarization or left and  right circular polarization. UHF, S-band, left, and right circular polarization.

6. Diplexer:
    VHF and S-band diplexers permit simultaneous transmission and reception of voice and telemetry signals with VHF and S-band.

The major mechanical characteristics of the antenna are:

1. Pedestal:
    Two-axis airborne mount, canted -35 deg from the longitudinal axis of the aircraft and mounted on the vertical plane.

2. Angular coverage:
    Azimuth: +100 deg relative to the aircraft heading. Elevation: -30 deg to +100 deg referenced to the horizontal plane.

3. Maximum Angular velocity:
    Azimuth: 90 deg/sec referenced to mount axis. Elevation: 24 deg/second referenced to mount axis.

4. Angular acceleration Elevation:
    52.5 deg/sec squared, referenced to aircraft, and azimuth: 180 deg/second squared.

    Throughout the ARIA program, with changing mission requirements, the Antenna Control system went through many upgrades and modifications.

    The most exciting time for the Antenna Operator was before acquisition of signal, AOS. It was during this time the operator would manually scan the parabolic dish in azimuth and elevation to acquire the target vehicle. If the target at the estimated time of AOS was not discoverable, the Antenna Operator became the center of attention.

Source: NASA
Additional Information: Randy L. Losey
Edited by: Randy L. Losey