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Manual Thrust Vector Control

This capability is provided during first- and second-stage ascent by substituting the inputs from the rotational hand controller for the automatic commands from guidance to gimbal the main engines and SRBs during first stage or the main engines during second stage. The digital autopilot remains active to process the flight crew's input. This is referred to in this mission phase as manual thrust vector control. MTVC is available at lift-off (SRB ignition command plus 0.365 second). One of the control stick steering push buttons at the glareshield/eyebrow panel F2 or F4 must be depressed before MTVC is available.

Once MTVC is activated, the vehicle is in a rate command/attitude hold mode in all axes. When the RHC is in detent, with MTVC selected, the vehicle is in attitude hold. The DAP holds the vehicle in the attitude it had when the RHC was in detent. A rate command equal to zero replaces the rate command generated in guidance and control steering. The attitude error for the DAP is computed by integrating the measured rates of the rate gyro assemblies. However, there are limits on vehicle rates and attitude errors. If the limits are exceeded when attitude hold is requested by placing the RHC in detent, attitude hold will not be initiated until the rates and errors are within limits.

When the RHC is removed from detent, a rate command proportional to the amount of deflection replaces the rate command previously generated. The attitude error is zeroed. The larger the deflection of the RHC, the larger the command. The flight control system compares these commands with inputs from the rate gyro assemblies and accelerometer assemblies (what the vehicle is actually doing-motion sensors) and generates control signals to produce the desired rates. When the commander or pilot releases the RHC, it returns to center and the vehicle maintains its current attitude (zero rates).

Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 04/07/2002
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