Antenna Control Console The most obvious feature of the ARIA is the radome which contains the 83-inch parabolic tracking antenna. The acquisition and tracking of telemetry signals is the function of this subsystem, which is controlled by the antenna control assembly (ACA), and the antenna operator. Bendix Corporation designed the original antenna control, Electrospace Systems designed the replacement antenna control in 1978. The replacement control was microprocessor based. There are two modes of antenna tracking. When the system is in automatic the antenna positioning is controlled by the antenna control assembly. When the system is in manual the antenna positioning is controlled by the antenna operator by the use of the hand wheels or joystick. The left hand wheel control adjusted the azimuth of the dish and the right hand wheel control allowed the operator to adjust the elevation of the dish. The antenna support pedestal attaches the antenna yoke assembly to the aircraft bulkhead. The pedestal is constructed with a 30 degree downward angle to allow the antenna to clear the radome when operating. Because of this downward angle the antenna control assembly has to perform a forward and backward coordinate conversion. Unless the azimuth of the dish is centered both the yoke and dish will have to be positioned to achieved point to any give place Automatic acquisition mode is selected by the antenna operator. Upon acquisition of the signal, the antenna system electronically simulates a conical scan of 3 dB off bore-sight to generate error signals that indicate in which direction the signal is off bore-sight. These error signals are routed to the telemetry/tracking receivers as amplitude modulation on the sum (data) channel, demodulated from the sum channel, and sent through the signal interface assembly to the tracking combiner/converter unit (TCCU) as tracking video. The TCCU converts the tracking video error signals to DC azimuth and elevation error voltages which are then routed through the antenna control assembly (ACA) to the servo amplifier, which in turn controls the clutches which engage drive motors to reposition the antenna. Trajectory Processor Unit The antenna may also be automatically controlled by the trajectory processing unit (TPU), which computes look angles (azimuth and elevation) for the antenna based on the proposed trajectory of the user's vehicle and the position of the ARIA. The versatility of the ACA is enhanced by the acceleration memory contained within the TPU. Should the vehicle's trajectory proceed non- nominally, the antenna will continue to track the vehicle and store the error buildup between the proposed trajectory and the actual trajectory in the acceleration memory. If the signal is then lost, the antenna will continue tracking along the original look angles, biased by the error buildup, until the signal is reacquired. Rate Memory If the TPU is not used on a mission and the antenna has been automatically tracking for at least 10 seconds, the antenna slew (motion) rate will be stored in rate memory. If the signal is then lost, the antenna will continue to move at the same rate as it did before loss of signal (LOS) for as long as 30 seconds, at which time the antenna will stop tracking and the LOS light will illuminate. This is a valuable feature during momentary blackouts. Manual Tracking During the actual data gathering interval of the mission, it is preferable to track automatically; but the need frequently arises to control the antenna manually, such as during pre-mission calibration (PMC), verification, before acquisition of signal (AOS), and after LOS. After placing the antenna system in manual mode, the operator has two ways to control the antenna hand wheels and joystick. The hand wheels are located on the front panel of the ACA, one for azimuth control and the other for elevation control. By monitoring the signal error meter, which indicates the antenna pointing error when a signal is present, the operator can manually correct the antenna position using the hand wheels. Typically, prior to AOS, the antenna operator will drive the antenna to the initial look angles and press ACQUISITION ENABLE (still retaining manual control). When the signal is acquired, the system will automatically switch to auto track. When this happens the operator will lose manual control of the antenna and must press ACQUISITION DISABLE to regain manual control. The joystick is a control stick which can individually or concurrently control the yoke and dish, and is most commonly used to drive the antenna out of stow (described below). Stow Mode When the antenna is not being used, it is stowed. In this mode, the antenna is automatically locked in position by two sliding pins (one for the yoke and one for the dish). The navigator's weather radar, which is located just aft of the antenna dish, is disabled when the antenna is not in the stowed position. This prevents the weather radar from being overloaded and damaged by energy being reflected off the rear of the dish. It also protects the flight crew from radiation exposure. Antenna References The antenna system requires both azimuth and elevation references in order to compute proper look angles. A compass card located in the ACA is slaved to the aircraft's Inertial Navigation System (INS) heading, and is used as the reference for azimuth (the antenna is therefore referenced to true heading). The INS heading simulator can be used to test the ACA in case of INS malfunctions and during pre-mission calibration. A gyroscope mounted in the antenna pedestal is used as the elevation reference. The gyroscope requires approximately 2 minutes to erect, so a 3-minute delay is introduced when the antenna system is powered on. The gyro is used to compensate for aircraft pitch and roll. If it should fail, the ACA has a zero pitch and roll simulator which can be actuated by the operator. These two references are used to keep the antenna pointed in true azimuth and elevation, regardless of the aircraft's heading, pitch, or roll. The dials at the antenna operator's position indicate true azimuth and elevation (compared to the mission control subsystem dials, which reflect yoke and dish position). The antenna position is limited to 100 degrees left or right of center in azimuth, and 100 degrees up to 30 degrees down in elevation. The maximum manual slew rate is 45 degrees per second, and the maximum automatic slew is rate is 17 degrees per second. Memory Bypass A memory bypass switch is provided to bypass rate and acceleration memory to enable antenna positioning by either the manual tracking mode or the automatic tracking mode.
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This Web Site Copyright © 2000-2017 Randy L. Losey - All other works Copyright © by their perspective owners
Antenna Control Console The most obvious feature of the ARIA is the radome which contains the 83-inch parabolic tracking antenna. The acquisition and tracking of telemetry signals is the function of this subsystem, which is controlled by the antenna control assembly (ACA), and the antenna operator. Bendix Corporation designed the original antenna control, Electrospace Systems designed the replacement antenna control in 1978. The replacement control was microprocessor based. There are two modes of antenna tracking. When the system is in automatic the antenna positioning is controlled by the antenna control assembly. When the system is in manual the antenna positioning is controlled by the antenna operator by the use of the hand wheels or joystick. The left hand wheel control adjusted the azimuth of the dish and the right hand wheel control allowed the operator to adjust the elevation of the dish. The antenna support pedestal attaches the antenna yoke assembly to the aircraft bulkhead. The pedestal is constructed with a 30 degree downward angle to allow the antenna to clear the radome when operating. Because of this downward angle the antenna control assembly has to perform a forward and backward coordinate conversion. Unless the azimuth of the dish is centered both the yoke and dish will have to be positioned to achieved point to any give place Automatic acquisition mode is selected by the antenna operator. Upon acquisition of the signal, the antenna system electronically simulates a conical scan of 3 dB off bore-sight to generate error signals that indicate in which direction the signal is off bore-sight. These error signals are routed to the telemetry/tracking receivers as amplitude modulation on the sum (data) channel, demodulated from the sum channel, and sent through the signal interface assembly to the tracking combiner/converter unit (TCCU) as tracking video. The TCCU converts the tracking video error signals to DC azimuth and elevation error voltages which are then routed through the antenna control assembly (ACA) to the servo amplifier, which in turn controls the clutches which engage drive motors to reposition the antenna. Trajectory Processor Unit The antenna may also be automatically controlled by the trajectory processing unit (TPU), which computes look angles (azimuth and elevation) for the antenna based on the proposed trajectory of the user's vehicle and the position of the ARIA. The versatility of the ACA is enhanced by the acceleration memory contained within the TPU. Should the vehicle's trajectory proceed non-nominally, the antenna will continue to track the vehicle and store the error buildup between the proposed trajectory and the actual trajectory in the acceleration memory. If the signal is then lost, the antenna will continue tracking along the original look angles, biased by the error buildup, until the signal is reacquired. Rate Memory If the TPU is not used on a mission and the antenna has been automatically tracking for at least 10 seconds, the antenna slew (motion) rate will be stored in rate memory. If the signal is then lost, the antenna will continue to move at the same rate as it did before loss of signal (LOS) for as long as 30 seconds, at which time the antenna will stop tracking and the LOS light will illuminate. This is a valuable feature during momentary blackouts. Manual Tracking During the actual data gathering interval of the mission, it is preferable to track automatically; but the need frequently arises to control the antenna manually, such as during pre-mission calibration (PMC), verification, before acquisition of signal (AOS), and after LOS. After placing the antenna system in manual mode, the operator has two ways to control the antenna hand wheels and joystick. The hand wheels are located on the front panel of the ACA, one for azimuth control and the other for elevation control. By monitoring the signal error meter, which indicates the antenna pointing error when a signal is present, the operator can manually correct the antenna position using the hand wheels. Typically, prior to AOS, the antenna operator will drive the antenna to the initial look angles and press ACQUISITION ENABLE (still retaining manual control). When the signal is acquired, the system will automatically switch to auto track. When this happens the operator will lose manual control of the antenna and must press ACQUISITION DISABLE to regain manual control. The joystick is a control stick which can individually or concurrently control the yoke and dish, and is most commonly used to drive the antenna out of stow (described below). Stow Mode When the antenna is not being used, it is stowed. In this mode, the antenna is automatically locked in position by two sliding pins (one for the yoke and one for the dish). The navigator's weather radar, which is located just aft of the antenna dish, is disabled when the antenna is not in the stowed position. This prevents the weather radar from being overloaded and damaged by energy being reflected off the rear of the dish. It also protects the flight crew from radiation exposure. Antenna References The antenna system requires both azimuth and elevation references in order to compute proper look angles. A compass card located in the ACA is slaved to the aircraft's Inertial Navigation System (INS) heading, and is used as the reference for azimuth (the antenna is therefore referenced to true heading). The INS heading simulator can be used to test the ACA in case of INS malfunctions and during pre-mission calibration. A gyroscope mounted in the antenna pedestal is used as the elevation reference. The gyroscope requires approximately 2 minutes to erect, so a 3-minute delay is introduced when the antenna system is powered on. The gyro is used to compensate for aircraft pitch and roll. If it should fail, the ACA has a zero pitch and roll simulator which can be actuated by the operator. These two references are used to keep the antenna pointed in true azimuth and elevation, regardless of the aircraft's heading, pitch, or roll. The dials at the antenna operator's position indicate true azimuth and elevation (compared to the mission control subsystem dials, which reflect yoke and dish position). The antenna position is limited to 100 degrees left or right of center in azimuth, and 100 degrees up to 30 degrees down in elevation. The maximum manual slew rate is 45 degrees per second, and the maximum automatic slew is rate is 17 degrees per second. Memory Bypass A memory bypass switch is provided to bypass rate and acceleration memory to enable antenna positioning by either the manual tracking mode or the automatic tracking mode.