Gemini Spacecraft

Organization Description

Gemini Pedistle 

Navigation vents

Horizon Scan Mode 

Horizon Scan Mode

Horizon sensor outputs (pitch and roll) are processed by the ACE to orient and hold the spacecraft within a desired attitude deadband during orbit. Pitch attitude is maintained automatically to within +/-5 degrees of the horizon sensor +/-5 degrees output, and roll attitude is maintained automatically to within +/- 5 degrees of the horizon sensor zero degree null. Control about the yaw axis is accomplished by commands from the attitude hand controller in the same manner as in the pulse mode. Pulse control about the pitch and roll axes is also available to supplement the automatic control. A -5 degree bias voltage is summed with the pitch input to the ACE to maintain the 5 degree pitch down orientation. When the attitude error (pitch or roll) exceeds the 5 degree control deadband, the output of the ACE on-off logic is a pulse firing command. The pulse time is 18 milliseconds and the pulse repetition frequency is dependent upon how much the attitude error exceeds the 5 degree deadband. A lag network in this mode provides a pseudo rate feedback for rate damping without having to use the power-consuming rate gyros.