Abstract: An arrangement for the attitude stabilization of flexible vehicles, such as ircraft and spacecraft. Such vehicles, due to their lightweight construction and/or large spatial extension or high degree of slenderness, have structurally weakly-dampened bending vibrations and/or torsional vibrations. For generating the forces and moments required for stabilizing such vehicle, discontinuously operating units are used. In one embodiment, for each vehicle axis, an observer or Kalman filter is employed for obtaining estimated values of the state variables of the vehicle system to be controlled. The observer has a first transfer function of at most third order. A state controller device is responsive to the observer for controlling the state variables. A modulator network is responsive to the state controller device wherein the modulator network has a relay characteristic.

Abstract: Transients and steady state error induced in maneuvering a satellite due to a disturbance torque caused by thrust mismatch or differential in the alignment of thrusters with respect to the center of mass are minimized by introducing a torque balancing bias at the input of a thrust modulator of the thrusters prior to sensing position or attitude error. The bias may instantly off-modulate the thruster control signal to cancel the effects of attitude transients before errors develop. Other axes thrusters may be on-modulated instantaneously to compensate for cross-axis torque. The bias may be introduced into the satellite control scheme by manual ground control or in automatic on-board compensation based on stored parameters obtained for example from calibration measurements. Specifically, the torque balancing bias may be developed by reference to thrust mismatch detected and stored during previous maneuvers, thus anticipating expected attitude error without actual detection thereof.

Abstract: Disclosed is a method and apparatus estimating yaw error and roll and yaw disturbance torques from measured roll error and yaw momentum on a continuous on-orbit basis in an orbiting satellite. The information thus obtained can be used to continuously correct for the yaw error by means of, for example, activating a magnetic torquer. Two control loops are used in this invention, a fast loop to damp nutations by changing momentum wheel speed, and a slow loop of the Luenberger observer variety. The latter is a yaw error correction loop which also serves to unload yaw momentum. The satellite in which the invention was first incorporated is of the type having three momentum wheels, all situated in the plane orthogonal to the roll axis. In normal operation, two wheels, each having major momentum component along the pitch axis and minor momentum component along the yaw axis, are operable.

Abstract: A closed-loop system for precisely regulating the speed of an electrically driven rotating body. A tachometer rotor, mechanically linked to the rotating body, is provided with p "teeth " around its periphery. A sensor produces a pulse signal upon passage of each of these teeth, to generate a cyclical tachometer signal having a frequency p times the frequency of rotation. A tachometer counter counts this signal and produces a single output pulse after every n.times.p pulses from the sensor, such that the same one of the p teeth is responsible for triggering each of the successive output pulses, and variations in spacing between teeth do not cause variations in the period of the counter output. A high frequency clock is counted by a second counter, which transfers its count to a storage register and resets upon each pulse from the tachometer counter, such that the count held by the storage register is a continuously updated, highly accurate digital representation of the period of the rotating body.

Abstract: A stability augmentation system utilizing a limited authority series actuator has an adaptive washout circuit which automatically reduces the effective washout system washout time constant as a function of attitude error or series actuator displacement. For small errors and for disturbances due to gusting winds, the system washout time constants are slow, thus providing good stability. For large errors the circuit smoothly reduces the time constants to keep the series actuators from saturating.

Abstract: A spacecraft or transfer vehicle for transportation of a payload from a space shuttle parking orbit to a higher operation orbit, wherein the transfer vehicle utilizes housekeeping subsystems integrated into the payload, to avoid unnecessary duplication of these subsystems, for such functions as power supply, guidance, control, and communications. The transfer vehicle disclosed includes a propulsion system with at least one low-thrust bipropellant liquid rocket engine, to provide a "soft" or low-acceleration ascent, and employs two tanking stages, each having four propellant tanks, arranged symmetrically in a circular configuration. The first stage of four tanks is jettisoned during ascent, and the second stage, including the remaining four tanks, the rocket engine, and related supporting structure, is separated from the payload when the operational orbit is reached.

Abstract: A method for changing the spin rate of a spinning spacecraft having a dynamic balancing mechanism which utilizes the communications channel between the spacecraft and the receiving terminal, the master index pulse generator on the spacecraft, and the spacecraft axial thrusters. To change the spin rate, a dynamic imbalance of a known wobble angle and phase is introduced by the dynamic balancing mechanism. An axial thruster is then fired for a predetermined time interval thereby coupling a portion of the axial thrust force into the rotational energy of the spinning body.

Abstract: Apparatus for controlling the pointing position of the payload platform of a dual-spin satellite. A torque motor which controls the relative position of the payload platform is controlled by means of a closed-loop feedback system which points the line-of-sight of the platform at a predetermined position on the earth. The control circuitry comprises position and rate sensing devices which monitor the relative position of the line-of-sight and the relative rotational rate of the payload platform. The line-of-sight of the platform is compared to signals indicative of the angular subtense of the earth. If the line-of-sight is pointed at the earth, then position command signals control the torque motor. If, however, the line-of-sight of the platform is not directed at the earth, then rate command signals are summed with the position command signals and subsequently applied to the motor.

Abstract: To ensure that a body will be independent of gravitation for the performance of tests, an evacuable protection box is provided which encloses contact free the body from all sides.The protection box has contactless scanning units to monitor the position of the body in its inside. It is conducted along three axes by a guiding system firmly connected to the spacecraft.The movements along each of the three axes is accomplished by driving means controlled by the scanning units so that the protection box follows changed positions of the body relative to the spacecraft.

Abstract: A spacecraft configuration including a service module which carries optical stabilizing equipment for stabilizing the spacecraft relative to two inertially fixed targets together with solar arrays rigidly attached thereto so as to extend in the orbital plane and never obstruct the field of view of the optical stabilization equipment. The payload module is attached to one face of the service module by means of rotary interface structure to be able to continuously point to the earth.

Abstract: A method of sun and earth acquisition for satellites which are stabilized in three dimensions and are equipped with acquisition sensors is provided. The method enables the acquisition of the earth and sun to be concluded as quickly as possible. The method includes a series of cumulative or alternative steps for changing the attitude of the satellite relative to the sun. These attitude changes are governed by a simple set of control equations. An arrangement for effecting the method is also provided.

Abstract: The torque from differential solar pressure acting on a spinning spacecraft body and tending to tilt the spacecraft about an axis transverse to the spin axis, is reduced or eliminated by shifting the center of gravity of the spacecraft axially or longitudinally of the spin axis in a direction toward the center of solar pressure.

Abstract: A system for compensating the disturbance torques applied to a satellite, which eliminates the requirement for a thruster control loop. The disturbance torque itself is used as the compensating torque in order to super-impose to the incidental misalignment of the solar panel arrays an artificial misalignment that can cause the momentum vector to be adjusted to the desired direction in order to restore the correct attitude of the satellite. The direction of the momentum vector is controlled in orbit only by solar sailing, that is by organizing at prescribed times suitable manoeuvres of one of the solar panels in order to adjust the solar panel array configuration when the roll angle of the satellite exceeds a determined threshold value.

Abstract: A satellite, especially a geostationary satellite which may be stabilized in its three major axes and which has a spin wheel or momentum wheel supporting a position control system and which also has an engine or propelling system, is controlled by actuating the spin or momentum wheel at the latest when the satellite is in a phase of being transferred from one orbit to another orbit. Thereafter, the satellite is rotated about its axis which extends in parallel to the axis of the spin wheel or momentum wheel whereby the rotational impulse of the satellite is smaller than that of the momentum wheel. The stabilizing of the satellite relative to the three major axes is then made at the point in time when the satellite is to change from one orbit to another orbit whereupon the engine system for reaching the new orbit is switched on. The thrust of the engine system is so dimensioned that the position control system intended for a subsequent mission retains its orientation even during the phase of changing orbits.

Abstract: A dual-spin spacecraft having a momentum wheel spinning relative to a platform to provide bias momentum utilizes cross products of inertia (POI) existing in the platform between the spinning axis and the transverse axes to achieve nutation damping. When the platform is rotating or is displaced from a reference the cross products of inertia are also rotating or are displaced causing thereby degradation of the optimum nutation damping time constant. Two or more phase shifting networks are provided to be sequentially coupled into a control loop to shift nutation signals to effect optimum nutation damping at selected positions of the rotating or displaced platform without substantial nutation damping time constant degradation.

Abstract: In a method for changing the spin of bodies released from an aggregate, the bodies are connected by straps or bars which serve as tension or compression members. Spin of the connected bodies results in either compressive or tensile forces in the connecting member. Those forces in turn provide torque which counters or enhances the spin and converts that spin to or from translational energy. Once the spin of the bodies has been changed a predetermined amount, the connecting member is released.

Abstract: The energy storage is effected kinetically. The system includes a first feedback loop with a time constant .tau.1 including a regulator connecting the supply busbar to a device for controlling momentum wheels used for the kinetic energy storage and the torque control. A second feedback loop, of time constant .tau.2, transmits velocity data .omega. from the momentum wheels to a processing unit, constituted by a microprocessor, which controls the wheel actuating device. A third feedback loop, of time constant .tau.3, supplies the processing unit with the data regarding the torque required by the satellite piloting device.

Abstract: An improvement in torque control systems for reaction wheel assemblies and the like used primarily for stabilizing space vehicles such as satellites including means for integrating the torque command signal and combining the integrated torque command signal with a feedback signal proportional to the angular speed of the rotor of the reaction wheel assembly thereby producing an error signal proportional to the difference between the integrated torque command signal and the angular speed signal. The error signal is coupled to the rotor spin motor which produces a resultant output torque that has been compensated for disturbance torques and other anomalies whereby the resultant torque applied to the rotor and consequently to the satellite is substantially equal to the commanded torque.