gyroscope de roulis

CONT: The scanner operates continuously, with its drive phase locked to the data system's master clock. An encoder signals the start of each scan. Aircraft roll compensation is accomplished by matching this start signal to the output of the roll gyro and delaying the start of data collection on the scan line enough to put the center pixel in the nadir position.
CONT: Background: Spacecraft Control. The incident was preceded by a routine calibration of the spacecraft's three roll gyroscopes (gyros). The three gyros, all aligned with the spacecraft roll axis, which is normally pointed toward the sun, measure incremental changes in roll attitude (orientation about the axis in space where the spacecraft rolls).