Abstract: A linear force actuator system for stabilizing a support structure employs a linear dc motor whose primary winding is driven by a pulse width modulation control signal representative of a force input, through which the secondary member of the motor which acts as an inertial mass, is to be controllably translated. For improved control accuracy, the actuator system of the invention employs a pair of feedback loops, one of which monitors the current in the motor's primary winding to maintain a constant force output to the secondary member and a secondary of which monitors long term deviations from the center of the secondary member and corrects for centering offsets. An opto-electronic position sensing arrangement monitors the movement of the secondary member whereby precise control of commutation of the coils of the primary winding and a smooth translation of the secondary member are obtained.

Abstract: Mechanical oscillations of a mechanism containing a stepper motor, such as a solar-array powered spacecraft, are reduced and minimized by the execution of step movements in pairs of steps, the period between steps being equal to one-half of the period of torsional oscillation of the mechanism. Each pair of steps is repeated at needed intervals to maintain desired continuous movement of the portion of elements to be moved, such as the solar array of a spacecraft. In order to account for uncertainty as well as slow change in the period of torsional oscillation, a command unit may be provided for varying the interval between steps in a pair.

Abstract: A nutation sensor and nutation control system using a relative spin phase sensor in a dual-spin stabilized satellite is disclosed. The relative spin phase sensor provides index pulses indicative of the relative spin phase and rate between the satellite rotor and platform. Nutation of the satellite perturbs the relative spin position of the rotor and platform and means are provided for analyzing index pulse arrive times to calculate nutation of the satellite. In the nutation control system, means are provided to apply a nutation damping torque to the satellite.

Abstract: The invention is a method of orienting a satellite in a geosynchronous orbit so as to direct a beam from an antenna mounted on the satellite to cover a desired target site, and pointing the beam axis at a desired bore site target. One embodiment of the method according to the invention includes a step of orienting the spin axis of a geosynchronous satellite at a direction angle which equals the inclination angle of the current orbital plane plus an adjustment or correction angle (.beta.), when the inclination angle is greater than zero. The correction angle is determined using one or both of the following equations:.beta.=BS-tan.sup.-1 {[ sin (bs-I)]/[6.61-cos (bs-I)]},or.beta.=.vertline.-(BS-tan.sup.-1 {[ sin (bs+I)]/[6.61-cos (bs+I)]}).vertline.,where, BS=the elevation angle of the bore site target in spacecraft coordinates, bs=the latitude of the bore site target, I=the inclination angle of the orbital plane with respect to the equatorial plane, and .beta.

Abstract: For controlling nutation of a three-axis stabilized satellite, the angular speed of a solar panel carried by the satellite is selectively and temporarily varied about an average value for modifying the inertia cross-product thereof and generating an angular momentum transverse to the angular momentum present in said body with a phase with respect to the nutation motion which tends to decrease the amplitude of the nutation motion.

Abstract: A nutation damping control for a dual-spin satellite is provided by tilting the axis of the rotor relative to the normal spin axis of the satellite and back a half nutation period later. The tilting is in the direction of the angular momentum vector component that is transverse to the rotor's spin axis.

Abstract: An active nutation damping system for a spacecraft may comprise a nutation sensor controlling an actuator, a thruster say, via a control system so as to produce nutation opposing torques. Following the realization that performance limits on known systems may be due to a simplistic dynamic analysis which assumes the spacecraft to be a rigid body when it may in fact comprise one or more oscillatory elements, for example a fuel tank in which fuel is able to `slosh` about freely, the damping system herein is operable to identify two types of nutation component, for one of which appropriate opposing torque components are generated while, for the other type, torque components are generated that, at first sight, would appear to increase the nutation components but which, in fact, improve the overall nutation damping performance.

Abstract: In a nutation damper system which includes a pendulum (30, 33, 34, 38) swingable at a natural frequency and a block element (35) which cooperates with the pendulum to damp nutations having a nutation frequency, a control member (40) electromagnetically coupled to the pendulum is provided for varying the natural frequency to a forced frequency substantially equal to the nutation frequency. The control member comprises an electromagnetic coil energized by a control signal having electric current produced by a control signal circuit which is proportional to a square of the nutation frequency. The block element may comprise either a permanent magnet or an electromagnet when a pendulum weight of the pendulum is of an electrical conductor. The electromagnet may intermittently be energized by a power source circuit. Alternatively, the block element may be of an electrical conductor when the pendulum weight is of a permanent magnet.

Abstract: The nutation damper comprises a closed flow path for a dense liquid, which may be a propellent and a pump for setting the liquid in periodic motion, thereby to dissipate or generate rotational energy controlled by a detector sensitive to a parameter relating to the nutation angle, according to the law of conservation of angular momentum. The principal application of the device is to the nutation damping of spinning spacecraft, in which the ratio between the moment of inertia about the spin axis and the lateral moment inertia is greater or less than 1.

Abstract: A method and apparatus for damping nutation in a spacecraft to essentially zero in less than one nutation period which has a spin axis, first and second transverse axes and a characteristic nutation frequency .lambda.. A time interval t.sub.1 after the transverse momentum of the spacecraft about one transverse axis, such as the Y axis has crossed zero, a torque of magnitude T.sub.Y is applied to the spacecraft about its Y transverse axis. After a time interval t.sub.2, the application of this torque is terminated. The time t.sub.1 =1/.lambda. cos.sup.-1 (h.sub.Y0 .lambda./2T.sub.Y) and the time t.sub.2 =2/.lambda. sin.sup.-1 (h.sub.Y0 .lambda./2T.sub.Y), where h.sub.Y0 is the peak body momentum about the Y transverse axis.

Abstract: A system for actively damping nutation of a satellite and/or aligning the pitch axis of a momentum bias satellite with some external reference includes a magnetic torquing means which is energized with currents of appropriate polarity and magnitude to effect the necessary torque to reduce nutation. A roll sensor produces signals proportional to the roll error of the satellite. A control signal is generated a predetermined time period after the roll error exceeds a predetermined threshold. The predetermined time period is a fraction x of the nutation period t.sub.n of the satellite or x+n(t.sub.n) where n is an integer.

Abstract: In a method of and apparatus for damping nutation of a spinning spacecraft (10), spin axis attitude disturbances are substantially reduced by controlling at least one nutation damping gas thruster (18) to fire with non-uniform gas pulses. During the beginning of a nutation control sequence, the duration of successive gas pulses is gradually increased (up pulsed) from zero to a predetermined maximum duration. The duration of successive pulses is then maintained constant for a time period. Finally, at the end of the nutation control sequence, the duration of successive gas pulses is gradually reduced to zero (down pulsed). Up pulsing of the gas thruster (18) is initiated in response to a predetermined maximum nutation angle measured by an accelerometer (20). Down pulsing of the thruster (18) is initiated in response to a predetermined minimum nutation angle. The number of variable and constant duration gas pulses delivered by the thruster (18) depends upon the mass distribution of the spacecraft (10).

Abstract: A preselected axis other than the axis of maximum moment of inertia of a momentum stabilized spacecraft is oriented for alignment with the total angular momentum vector of the spacecraft by rotating one or more rotors to a critical rate of rotation. The rotation of the rotor or rotors is maintained at the critical rate to effect the desired rotation. The axis of the rotor or the effective angular momentum vector of the resultant momentum of a plurality of rotors is aligned with the axis of the desired spacecraft orientation. Energy dissipation assures stability by dissipating energy on the spacecraft body at a faster rate of dissipation than the rate of energy dissipation on the rotor.

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: An attitude control and stabilization system for momentum biased satellites utilizing a pair of counterrotating flywheels mounted parallel to its yaw axis. The speed of one of the wheels of the pair is controlled by sensing and correcting the roll axis errors of the satellite.

Abstract: An apparatus for controlling nutation motion in a spinning body, comprising an angular accelerometer having its input axis perpendicular to the spin axis of the body, a flywheel having an axis of rotation perpendicular to the axis of the accelerometer and to the spin axis of the body, and a motor for driving the flywheel to attenuate or build nutation. The motor is controlled by circuitry that monitors the output of the angular accelerometer and drives the motor clockwise or counterclockwise during predetermined nutation angles synchronized to the zero crossover points of the accelerometer signal and centered about the nutation peaks. In one embodiment, the motor drive is phased to damp nutation motion to zero for stabilization.

Abstract: A controller for the attitude stabilization of a satellite. The controller odifies the action of a first control circuit by responding to the signals of attitude .phi. and angular velocity of attitude .phi. developed by the first control circuit. A second control circuit includes a comparator, two Schmitt trigger circuits, two AND elements and two OR elements. Signals from the AND elements and uncorrected thrust nozzle control signals from the first control circuit are supplied to the OR elements. The output of the OR elements control the thrust nozzles of the satellite.

Abstract: The invention relates generally to an improved system for sensing and compensating for external disturbance forces acting on a satellite while in orbit. A proof mass member is housed within an enclosure and shielded from external, non-gravitational forces. The proof mass is electromagnetically levitated to move in a purely gravitational orbit, along an axis aligned with the satellite's velocity vector. The proof mass is subjected to a controlled magnetic biasing field and is caused to have a constant reaction to the resultant biasing force, by means of a thermal control system which maintains constant resistivity of the proof mass, during operation. The position of the proof mass with respect to its axis is detected optically and is utilized to control the firing of spacecraft thrusters. As a result, the satellite is caused to maintain a substantially constant position relative to the proof mass and thereby also is caused to follow a purely gravitational orbit.

Abstract: A nutation damper apparatus capable of damping small nutation angles in a satellite. A permanent magnet mounted on the free end of a pendulum arm oscillates back and forth parallel to an adjacent conductive plate in the form of a circular segment having a cross-sectional area that increases from the center to its lateral ends, and induces in the plate a magnetic flux which is proportional to the deviation angle of the pendulum from its rest position.

Abstract: A motor active nutation damping system employing a rotor mounted accelerometer, a platform/rotor relative rate sensor, a despin motor and a controller. In the presence of nutation, the accelerometer senses a sinusoidal acceleration whose amplitude is proportional to nutation angle and whose frequency is rotor nutation frequency, i.e., the rate at which the transverse angular momentum vector appears to rotate in rotor fixed coordinates. The controller multiplies the filtered accelerometer signal by a square wave at relative rate generated by the relative rate sensor to obtain a signal consisting of sinusoids at platform nutation frequency and higher order frequencies.

Abstract: This invention relates to an attitude stabilizing system for a rod-shaped satellite in which stabilization is achieved by use of a spinning energy dissipator. The system can operate by being mounted on the rotor of a dual spin satellite or by being connected to the main body of the satellite through a motor and bearing assembly. In the latter situation, the stabilizer acts both as a nutation damper and a momentum source and thereby eliminates the need for an additional rotor element to provide the spacecraft momentum. The spinning energy dissipator may be designed to use four identical wheels mounted coaxially with and at the ends of the arms of a cruciform structure. The structure may then be spun about the axis perpendicular to the arms, to provide angular momentum along the spacecraft spin axis. In the event of any spacecraft nutation, the wheels experience the torques produced by inertial forces.