Abstract: Method and apparatus for calibration of a set of rate gyros on a three-axis stabilized satellite in orbit, the satellite including an attitude sensing system including the set of rate gyros, a set of actuators and control logic adapted to apply to the set of actuators control signals U derived from measurement signals M supplied by the attitude sensing system. From a time t.sub.0 satellite attitude errors (E1) relative to a reference frame of reference and constant drifts (E2) of the set of rate gyros about three axes (XYZ) of the satellite are estimated conjointly. The estimated values of the attitude errors and the difference between the measured speeds (.omega.) of the set of rate gyros and the estimated values of the constant drifts are applied in real time to the control logic and these estimated values of the constant drifts are stored when they become constant to within a first predetermined tolerance and the estimated values of the attitude errors become constant to within a second tolerance.

Abstract: Earth acquisition from the Sun pointing attitude starts with angular displacement of the satellite so that, in the field of view of a Sun sensing system, the direction of the Sun is brought into an orientation S' such that subsequent rotation of the satellite about the orientation S' brings the Pole Star into the field of view of a star sensing system whose optical axis is substantially parallel to the pitch axis. During this rotation the stars sensed are compared with those in a catalog containing, in addition to the Pole Star, stars likely to be encountered upon such movement. At least two of these stars are identified and then the Pole Star is captured. The satellite is then rotated in pitch until the Earth is sensed and captured.

Abstract: A roll/yaw attitude control system for a three-axis stabilized satellite in an at least approximately Equatorial orbit embodies a processor circuit connected between a roll, yaw and pitch attitude sensing device including a terrestrial sensor and a stellar sensor adapted to detect the Pole Star and an actuator device having a kinetic moment system substantially oriented along the pitch axis and a magnetic dipole generator system disposed at least approximately in a roll/yaw plane. The processor circuit embodies a short-term roll/yaw control loop adapted to estimate the roll and yaw attitude angles and angular speeds and to determine set point signals for some elements of the actuator device and a long-term roll/yaw control loop adapted to estimate roll/yaw attitude angles and external disturbances and to determine a dipole signal to be applied to the magnetic dipole generator system or to backup actuators.