Abstract: Navigation satellite receiver measurements of the acceleration of a moving vehicle are used to derive valuable attitude information about the vehicle. Three-dimensional accelerometer measurements aboard the vehicle are used to determine the specific force vector in the bow frame. The navigation satellite receiver measurements allow determination of the specific force vector in the earth-fixed frame. The specific force vector measured in both vehicle and earth-fixed frames can be used with additional information to derive vehicle attitude.

Abstract: A method and apparatus determines attitude of a satellite (52) or other communications device traveling in a determinable path. The method comprises determining orientation data describing directions of one or more narrow-beam RF or laser communications channels (223, 225, 231, 233, 241, 251, 253, and 261; FIG. 2) and using the orientation data and known position of the satellite to determine the attitude of the satellite. The apparatus comprises one or more directional transmitters and receivers (310, 312, 314, 316, 318, and 320; FIG. 3) coupled to controller (330), where controller (330) accepts orientation controller data from the one or more directional transmitters and receivers and determines the satellite's attitude based on the orientation controller data and the known positions of the transmitters and receivers.

Abstract: A magnetic sensor that measures the angle of the sensor's sensitive axis relative to a local magnetic field compensates the navigation solution of a MEMS-IMU/GPS navigation system. A stable navigation solution is thereby maintained. The magnetic sensor is mounted on a body axis of the vehicle perpendicular the spin axis of the vehicle. As the vehicle spins, the magnetic sensor provides an analog output voltage that varies sinusoidally with vehicle roll with the zero crossings occurring when the sensor's sensitive axis is perpendicular to the local magnetic field. The magnetic sensor measurements combined with knowledge of the local magnetic field relative to the local level reference are used to correct the navigation solution's roll error. Following high rate sampling of accelerometers and gyros, and algorithm to computational de-spin in the navigation solution is executed whereby navigation processing may be implemented with a non-rolled vehicle body frame algorithm.

Abstract: A method for the on the whole minimum-fuel, computer-assisted control of an optionally determined number of thrusters, arranged as desired on a spacecraft, is to be specified, which method solves this linear optimization problem within the shortest possible time by reducing the computation expenditure. The method depends on the dual simplex algorithm and a suitably provided dual permissible start table. The dual permissible start table is set up on the basis of a previously computed optimum table and the transformation of the actual forces-moments vector belonging to the selected start table. Specific processing steps in the dual simplex algorithm are either not needed at all or are substituted with processing steps that require considerably less computation expenditure. Finally, a reduced table is used in place of the simplex table.

Abstract: A method is disclosed for targeting a satellite orbiting earth between to sites on earth based on an access time that is transmitted from a ground station. Control momentum gyros are used to change the satellite's attitude for targeting. A gryo rate is selected based the longest time to target. The longest time is a value selected from the access time, the time to reach the target based on the satellite's attitude and the time to reach the target based on the gyro rate.

Abstract: Disclosed is a method and apparatus (1'; 1") for tracking a stellar body (22) using a telescope (9; 32) of a spacecraft (e.g., a satellite) (10; 10"). In accordance with an embodiment of the invention, the telescope (9; 32) is provided with gimbal supports (18a; 18b), and is maneuverable relative to the spacecraft (10; 10'). The stellar body (22) is acquired by the telescope (9; 32) so that the stellar body (22) is within the field of view (FOV) of the telescope (9; 32). After the stellar body (22) is acquired, an operation is performed for controlling the attitude of the spacecraft (10; 10') to within pre-established deadband limits, and, as a result, the spacecraft (10; 10') and telescope (9; 32) are each assumed to have a desired orientation relative to the stellar body (22).

Abstract: Spacecraft cost, volume and weight are reduced with gyroscope calibration methods that can be effected with structures (e.g., a single-axis Sun sensor and a wheel system) which are typically carried by spacecraft for other purposes. In a method embodiment, these methods include an initial step 1) of calibrating a selected gyroscope and subsequent steps for each uncalibrated gyroscope of: 2) slewing the spacecraft by a slew angle and controlling attitude with the uncalibrated gyroscope for a selected time period to thereby couple its drift into the inertial axis of a calibrated gyroscope, 3) backslewing the spacecraft to return the calibrated gyroscope to its inertial axis, and 4) measuring an error angle generated by the uncalibrated gyroscope during the selected time period (e.g., with a Sun sensor or with the calibrated gyroscope).

Abstract: An attitude sensing system utilizing simplified techniques and apparatus includes a spacecraft control processor which receives signals from an inertial measurement unit and two attitude sensors. The spacecraft control processor calculates a time-varying gain matrix for estimating attitude errors and gyroscope drifts corresponding to the axes of the inertial measurement unit. In special cases where the separation angle between the attitude sensor vectors is less than approximately 10 degrees, the time-varying gain matrix is computed as a fixed gain matrix and a corresponding desensitizing factor.

Abstract: The present invention provides a system (200) for determining the ephemeris and attitude for a spacecraft based on optical payload pointing directions and the ephemeris of other spacecraft. An ephemeris determining subsystem (300) obtains ephemeris data (308) for one or more reference spacecraft. Optical payload pointing information (306) is obtained for the optical payload pointed to the reference spacecraft. The spacecraft ephemeris (312) is then calculated with ephemeris determination algorithms (302) based on the ephemeris data (308) and optical payload pointing information (306). Other available information, such as stored results of previous measurements and calculations, time (310), spacecraft attitude (304), information from non-payload sensors and ranging information may be used to enhance the accuracy or decrease the complexity of the ephemeris calculations. Spacecraft attitude can also be determined using reference spacecraft ephemeris data and optical payload pointing information.

Abstract: A method for inertially aligning a spacecraft along an axis, comprising the steps of using quaternion feedback control to reorient the spacecraft, and during the step of reorienting, using rate integrating gyroscopes in a pulse rebalance loop. The method operates to orient the spacecraft along an inertial direction of interest by the steps of operating a sensor to provide an initial fix on the inertial direction of interest; repetitively determining a difference between a commanded quaternion and a quaternion estimated based on sensed angular rates; and selectively applying torques to the spacecraft so as to drive the difference towards zero such that a spacecraft vector is aligned with the inertia direction of interest, thereby orienting the spacecraft. One mode of operation maintains the spacecraft fixed in orientation, while another mode of operation rotates the spacecraft about the direction of interest by using a bias-rate blind quaternion propagation technique.

Abstract: Autonomous slewing of a spacecraft about a desired axis using reaction wheels permits a maximum slew rate without wheel saturation even with one wheel failure. The slew is carried out if the total angular momentum of the spacecraft is less than a momentum storage threshold determined from reaction wheel availability. The momentum threshold may be found as the radius of a sphere inscribed in a polyhedron in momentum space, the polyhedron based on the maximum single wheel capacity and the geometry of the reaction wheel system as well as the reaction wheel availability. The momentum available for the slew is determined from the total angular momentum and the availability of each reaction wheel. The slew rate magnitude and slew direction are based on the available momentum.

Abstract: A method for controlling orbiting spacecraft uploads a plurality of parameters to an onboard processor, the parameters including a plurality of quaternion elements describing an inertial to orbit reference frame, and including radial position, radial velocity and angular rate of the spacecraft. Parameters are input for processing one of a plurality of propagation algorithms, preferably calculating said propagation algorithms with the uploaded parameters, computing enhanced time of day vectors, and computing ground time of day angles from the enhanced time of day vectors for adjusting the payload pointing angle, such as an antenna pointing angle, of the satellite. Preferably, the calculating step comprises integrating an orbital state vector with a second order Runge-Kutta integration algorithm. In addition, enhanced time of day fault processing provides an internal check on integration accuracy and is checked every time of day update.

Abstract: In a process for identifying an incorrectly measuring sensor which is part of a sensor arrangement on a spacecraft, external directional vectors are measured, relative to external objects, such as the earth, the sun or selected stars, or to external field vectors, such as the earth's magnetic field. Based on actual time and space coordinates of the spacecraft, respective actual external directional vectors are calculated with respect to an inertial system of coordinates, and the angles between these vectors are determined. These angles are compared with corresponding angles which exist between the directional vectors measured by a function of the sensor arrangement relative to a spacecraft-fixed system of coordinates. Based on this comparison a sensor which may measure incorrectly can be identified reliably.

Abstract: A method and apparatus for estimating attitude sensor bias in a satellite system uses attitude sensors and a spacecraft control processor. Attitude sensors provide output signals, which may contain bias. The present invention interprets the signals, determines the bias present in the signals, and generates an output signal to offset the bias in the signals from the attitude sensors, thereby leading to more accurate positioning of the satellite employing the present invention.

Abstract: An attitude determination system for an artificial satellite capable of performing star identification without need for the aid of ground station includes an image processing module (17) for processing star images observed at predetermined time points by a star sensor (16) mounted on the artificial satellite (1) for arithmetically determining direction vectors of the observed stars, a rotation estimating module (18) for estimating a rotational motion of the artificial satellite (1) between an attitude of the artificial satellite at a predetermined time point and an attitude of the artificial satellite at another time point, an elongation estimating module (19) for estimating elongations between the direction vectors of plural stars the images of which are picked up at a same time point by the star sensor and estimating the elongations between the direction vectors of plural stars the images of which are picked up at different time points by the star sensor on the basis of the estimated rotational motion, a st

Abstract: A three axis attitude readout system for geosynchronous spacecraft operating at geosynchronous and other orbit altitudes has a two axis sun sensor, a two axis Polaris star tracker, and an infrared single axis earth sensor for use when the sun is behind the earth. The three sensors cooperate with each other such that each sensor has characteristics overcoming inherent weaknesses in the other sensors. The overall system results in a highly accurate three axis readout which could not be achieved by using any of the three sensors alone. The sensor system is designed to be of low weight, low volume and low power consumption.

Abstract: A method for inertially aligning a spacecraft along an axis, comprising the steps of using quaternion feedback control to reorient the spacecraft, and during the step of reorienting, using rate integrating gyroscopes in a pulse rebalance loop. The method operates to orient the spacecraft along an inertial direction of interest by the steps of operating a sensor to provide an initial fix on the inertial direction of interest; repetitively determining a difference between a commanded quaternion and a quaternion estimated based on sensed angular rates; and selectively applying torques to the spacecraft so as to drive the difference towards zero such that a spacecraft vector is aligned with the inertia direction of interest, thereby orienting the spacecraft. One mode of operation maintains the spacecraft fixed in orientation, while another mode of operation rotates the spacecraft about the direction of interest by using a bias-rate blind quaternion propagation technique.

Abstract: A transmitting apparatus for use in non-geostationary satellites which allows compliance with the restrictions placed on PFD even when the Earth is located between the geostationary satellite and the non-geostationary satellite. The transmitting apparatus 10 for use in non-geostationary satellites having a transmitting section 16 which sends a transmitting signal to the geostationary satellite, comprises an Earth-sensing section 19 for detecting the presence of the Earth in the direction of transmission and a transmission direction-shifting section 20 for shifting the direction of transmission of the transmitting signal in response to detection of the Earth-sensing section 19 to prevent the Earth from being exposed to the transmitting signal. Instead of the transmission direction-shifting section 20, there may be used a power supply-suspending section which automatically suspends power supply to the transmitting section 16 thereby stopping transmission of the transmitting signal.

Abstract: A method for controlling the direction of a spacecraft of the type having a controller for calculating thrust forces comprises a plurality of thrusters disposed on said spacecraft in a spaced relationship relative to one another and aligning and locating each of said plurality of thrusters at a predetermined angle on said spacecraft relative to first, second and third orthogonally oriented axes such that the firing of any given pair of thrusters produces a torque about one of said spacecraft axes; and firing of all of said plurality of said thrusters in equal amounts at one time to cause the spacecraft to move in a linear manner along one of said three orthognally disposed axes.

Abstract: Spacecraft attitude is efficiently controlled by utilizing spatial noise and temporal noise in the calculation of gains to a Kalman filter. Spatial noise is modeled in a dynamic fashion so as to provide optimal spatial noise attenuation.

Abstract: Control moment gyros in an array are rotated to reorient a satellite. A pseudo inverse control is employed that adds a term to a Moore-Penrose pseudo inverse to prevent a singularity.

Abstract: The present invention provides an improved intelligent control apparatus and method of a satellite where the orbit and attitude control are executed autonomously onboard the satellite. The satellite makes an intelligent decision whether the satellite should be in normal operations mode or in the contingency mode, and if the satellite is in the normal mode, then attitude and orbit of satellite is controlled autonomously to maintain the predetermined attitude and orbit. If the satellite is in the contingency mode, then the satellite decides whether there is collision danger and executes emergency orbit maneuver automatically if such danger exists. Furthermore the satellite checks for the anomaly functioning sensors and actuators, and discontinues their usage.

Abstract: An earth sensor assembly for an orbiting spacecraft which includes a two dimensional microbolometer area array detector as the detective source for capturing full or partial infrared (IR) images of the earth. The earth sensor assembly further includes an input optic head assembly for collecting incident radiant power emitted from the earth and for directing it to a focal plane of the microbolometer area array. The microbolometer detector converts the detected radiant power into electric signals. Also included are sensor electronics and data processing means for processing the converted signals and determining the attitude of the spacecraft relative to the earth. Also disclosed is an algorithm for processing the earth image information generated by the microbolometer area array and for determining the three axis attitude (pitch, roll and yaw) of the spacecraft.

Abstract: A system and method for acquiring Sun pointing in a three-axis stabilized spacecraft including slewing at least one solar wing until the Sun is detected, determining an initial Sun vector, performing one or more rotations of the spacecraft body so as to bring the instantaneous Sun vector coincident with a preferred final Sun vector, at least one rotation about an optimal axis, and slewing at least one solar wing to a preferred attitude relative to the Sun. In one embodiment, the optimal axis is chosen so as to minimize the time required to achieve an optimal thermal attitude. In another embodiment, the optimal axis is chosen so as to minimize the time required to align the instantaneous Sun vector with the final desired Sun vector. In a further embodiment, the optimal axis is chosen so as to maintain Earth lock.

Abstract: A pseudo gyro emulates mechanical gyros by software processes by processing space system appendage measurement data and reaction wheel tachometer data within reference and control systems of a satellite using principals of conservation of momentum to compute the vehicular bus angular velocity rate data by accounting for the momentum transfer between the satellite, the bus, and the appendages for providing accurate relative vehicular position and angular velocity rate data as an integral part of attitude reference and control systems now having higher reliability, longer life times, lower power consumption, and more accurate vehicular angular velocity rate data generated within high bandwidth operations.

Abstract: An earth orbiting satellite is enabled to assume a "survival mode" of operation in which its x axis is aligned with the sun by observing characteristics of the movement of the frame of the satellite (e.g. its x axis) relative to the sun and performing calculations based on those operations. A more accurate result is achieved if a deliberate offset is introduced between the mean direction of the x axis and the sun's direction. The control arrangement for positioning the x axis with this offset is preferably adaptive, resulting in control of the satellite's thrusters so as to produce oscillation of the x axis in a way which allows suitable measurements to be taken.

Abstract: An onboard star tracking system is used to provide continuous attitude data based on a fixed star catalog. An orbital position reference for the sensed star data is estimated from uploaded data. The attitude is calculated based solely on the star sensor data referenced to the estimated orbital position and compared to mission attitude to generate an attitude adjustment.

Abstract: One or more deployable thermal panels (24, 28, 70) are actively controlled throughout the orbit of a satellite (20) to provide thermal dissipation. Adjusting the incident angle between the panel (24, 28, 70) and the sun and controlling the flow of fluid through optional flexible heat pipes loads and unloads heat to provide thermal stability for components (62) which have special thermal requirements. An optional antenna panel (70) on a nadir side (64) of the satellite (20) offers an antenna side (74) on one surface and a thermal radiating side (72) on an opposing surface. In addition, thermal panel movements are controlled (96) to provide counter-disturbance torques (140).

Abstract: A feedback motion compensation (FMC) component for use in a spacecraft having a payload. The FMC component includes a controller having sensor data inputs and an open loop dynamics model that is driven by actuator commands to produce a high accuracy attitude estimate suitable for payload motion compensation.

Abstract: A spacecraft ground loop controller (GLC), located on the Earth, interfaces with a satellite ground station receiving spacecraft telemetry from the downlink baseband equipment and automatically sending spacecraft commands through the command uplink baseband equipment to control the attitude of an orbiting spacecraft and achieve partial orbit control using commanded thruster firings and magnetic torquer polarity and magnitude. A cooperative approach of using all available thrusters, of both the primary and redundant strings, provides greater fuel savings.

Abstract: A system for autonomous on-board determination of the position of an earth orbiting satellite consists of a biaxially measuring earth sensor which defines the z-axis (yaw axis) of the satellite and of several biaxially measuring sun sensor measuring heads which are arranged on the satellite structure such that, with the exception of earth shadow phases, they supply a direction vector measurement. Out-of-plane movement of the satellite is propagated by means of a precise model of the satellite dynamics including natural disturbance forces and thrusts during maneuvers on board. In order to compensate sensor uncertainties and the effects of thermal deformations, the satellite orbit is precisely measured at regular intervals (approximately 3 months), and by means of this information, a calibration function (time function for a day) for compensating measured values is determined.

Abstract: The attitude (yaw, pitch and roll) of a home satellite is determined using position signals, derived from a GPS receiver on the home satellite and GPS receiver on other satellites, that are transmitted between the home satellite and the other satellites by an intersatellite communications link using gimbaled transceivers on the satellites. The home satellite determines its attitude from the gimbal elevation and azimuth and the position vectors between the satellites.

Abstract: For a switching of a magnitude of system gain in the driving of a load by a control system, a method of inhibiting formation of switching transients has a step of distinguishing between an estimate of a plant state, such as the attitude of a spacecraft, and an integral control state which allows the control system to provide actuation in response to long term disturbances, such as solar pressure, in operation of the system. In the case of a feedback configuration to the system with controller in a forward branch and an estimator in a feedback branch, a loop error signal serves to drive an actuator of the load via the controller. The method includes a further step of evaluating a portion of a controller input signal which is exclusive of an integral control state and which comprises a difference between a desired state and an estimate of the plant state.

Abstract: An earth chord sensor on board a satellite produces an electrical pulse as the satellite spins and sweeps the sensor across the earth. If the satellite is spinning at a low spin rate or if the sensor is measuring a long earth chord, the sensor produces an irregular pulse with sharp voltage peaks rather than a near trapezoidal pulse. The present invention digitizes the output of the earth chord sensor and a processor processes the digitized output through a data buffer to detect the leading edge peak and trailing edge peak of the pulse. The processor may detect the peaks through parabolic curve fitting among the digitized data points of the sensor output. The processor calculates the earth chord time as the time width of the pulse between the detected leading edge peak and trailing edge peak of the pulse and transmits, by telemetry, the calculated earth chord time to a ground station for use in satellite positioning.

Abstract: The sun search method for a satellite stabilized in three axes according to the invention uses a sun sensor device with a visual field possibly containing gaps, and a rotational speed gyro which measures in a measuring axis that is oriented arbitrarily. A regulating law with the form .tau.=-kGG.sup.T .omega. is used (.tau.=regulating torque, k=amplification factor, G=directional vector of measuring axis of rotational speed gyro, .omega.=rotational speed vector of the satellite). A rotational wheel momentum H which is not parallel to the measuring axis, is generated with the aid of an additional flywheel device.

Abstract: A multiple detector array is positioned in a satellite orbiting the earth for determining the attitude of the satellite with respect to the earth by detecting the earth's horizon. The multiple array of spaced detectors are mounted on a horizon sensor with a space detector viewing space, a horizon detector, with a field of view straddling the horizon and outer space space, a detector viewing the earth, and a gradient detector viewing the earth. Individual signals from these detectors are amplified and processed such that any gradients between the two earth viewing detectors are used to provide radiance compensation to correct for radiance errors in sensing the true position of the horizon.

Abstract: A method for simultaneously controlling satellite nutation, sun angle and attitude walk using a dual-slit sun sensor and thrusters. The sun angle and nutation angles are computed from sun sensor data, and the thrusters are fired when their use improves both sun angle and nutation. Precession around the sun line is controlled by constraining firing, in the simplest case, firing only when the angular momentum is precessed directly toward or away from the sun. Precession maneuvers are implemented by commanding a new sun angle and precession plane spin phase.

Abstract: Three rate gyros are mounted to a ballistic body to provide an autonomous navigation system. A roll gyro, a yaw gyro and a pitch gyro are rigidly fixed to the ballistic body. Each gyro is arranged to be responsive to a roll rate about an input axis that is substantially orthogonal to any other gyro. The roll-rate gyro has its input axis aligned parallel to the body spin axis. An on-board processor utilizes recursive Kalman-filtering to determine the roll angle, i.e., the local vertical direction, from the gyro outputs.

Abstract: A triaxially stabilized earth oriented satellite is provided with an attitude control system. The attitude control system contains a controller, final control elements for generating control torques around each of three axes of a system of coordinates (principle axes x, y, z) fixed relative to the satellite. Additionally, the attitude control system comprises, as measuring transducers, exclusively a direction vector measurement device, like a magnetometer or star sensor, a sun sensor array and an earth sensor. The process of the invention makes use of the apparatus as noted above and includes the steps of:A. determining an estimate for the rotating velocity of the satellite from a direction vector measurement;B. searching for the sun, depending on the size of the field of view of the sensor, by one or two search rotations at right angles to the optical axis;C. adjusting the direction of the sun relative to the optical axis; andD. adjusting the direction vector measurement to a reference direction S.sub.

Abstract: A transmitting apparatus for use in non-geostationary satellites which allows compliance with the restrictions placed on PFD even when the Earth is located between the geostationary satellite and the non-geostationary satellite. The transmitting apparatus 10 for use in non-geostationary satellites having a transmitting section 16 which sends a transmitting signal to the geostationary satellite, comprises an Earth-sensing section 19 for detecting the presence of the Earth in the direction of transmission and a transmission direction-shifting section 20 for shifting the direction of transmission of the transmitting signal in response to detection of the Earth-sensing section 19 to prevent the Earth from being exposed to the transmitting signal. Instead of the transmission direction-shifting section 20, there may be used a power supply-suspending section which automatically suspends power supply to the transmitting section 16 thereby stopping transmission of the transmitting signal.

Abstract: An apparatus for determining the bank angle of an aircraft and method includes a receiver for receiving navigational signals from NAVSTAR/GPS satellites in orbit about the earth, a signal processor for demodulating the satellite navigational signals, an arrangement for determining a sensitivity value, the sensitivity value being defined as the amount of bank angle displayed per rate of change of track heading, an arrangement for determining the rate of change of the aircraft track heading from the navigational signals, an arrangement for determining the bank angle of the moving aircraft from the sensitivity value.

Abstract: A three-axis attitude orientation system for a spacecraft is described. The single sensor provides roll and pitch information by locating the centroid of the earth and using this as a reference point. The system determines yaw by tracking the position of stars which appear in the field of view around the earth. Three-axis attitude is determined through ultraviolet imaging of the earth's limb and adjacent stars. A diffractive optics sensor and intensified CCD array are utilized for this purpose.

Abstract: A spacecraft traveling in a volume of space receiving radiation from the sun and encountering an undesired force. The spacecraft has a solar panel movably attached to said spacecraft. The spacecraft further includes a solar panel controller which controls the movement of the solar panel, wherein the controller moves the solar panel in a time modulated manner so that a torque is generated which compensates for the undesired force.

Abstract: A system for precisely determining directionality of an output beam includes a beam source and a body position identifier facing opposite directions, with a grating rhomb positioned to provide an attenuated sample beam from the beam source into the oppositely directed body positioned identifier. In the preferred embodiment, the beam source is a pulsed laser source and the body position identifier is a star tracker for forming a stellar map. The grating rhomb includes first and second grating members. The first grating member extends across the optical path of the output beam and has a geometry to diffract a minor portion of the output beam intensity while passing a major portion of the output beam for continued propagation in a first direction. The second grating member is positioned to traverse the field of view of the body position identifier.

Abstract: A spacecraft (10) carries a solar panel (17) which rotates to follow the sun, and also carries various thrusters (20). Thruster plume impingement on the solar panel affects the torque applied to the spacecraft body (12) in a manner which depends upon solar panel angle. The errors in the thrust during stationkeeping tend to perturb attitude, especially early in the maneuver, because of the delay inherent in the attitude control loop. A torque bias is summed with the residual torque demand signal to correct for the errors in torque. The torque bias signal is generated by a Fourier model of the torques, updated by an adaptive tuning filter, so that successive stationkeeping maneuvers progressively adapt the amplitude and phase of the Fourier coefficients in a manner which tends to minimize the residual torque demand and attitude error. Thus, the torque bias signal automatically approaches the correct value.

Abstract: The life of a target satellite is modified, i.e., extended or terminated by docking an extension spacecraft with the target satellite to form a docked satellite-spacecraft combination. The extension spacecraft is docked with and mechanically connected to the target satellite and includes guidance, navigation, and control systems for performing the rendezvous and docking maneuvers and for controlling the position of the docked spacecraft-satellite combination. The extension spacecraft also includes an onboard propellant supply for accomplishing the rendezvous and docking of the spacecraft with the satellite and for controlling the position of the docked spacecraft-satellite combination. A remote cockpit system is provided to permit human control of the extension spacecraft during proximity operations.

Abstract: A method and system of damping nutation of a spacecraft (20) having a desired spin axis along a first principal inertia axis utilizes a momentum source (28) oriented along a second principal inertia axis perpendicular to the first principal inertia axis. An angular rate of the spacecraft (20) is sensed along an axis transverse to both the first principal inertia axis and the second principal inertia axis. An angular rate signal representative of the angular rate is generated. The angular rate signal is processed to form a control signal representative of a desired torque to drive the momentum source. The desired torque has a first additive component proportional to a derivative of the angular rate to critically damp the nutation under an at least second order model of the spacecraft (20). The momentum source (28) is driven in dependence upon the control signal.

Abstract: A method and apparatus for steering a low-earth-orbit communication satellite requiring sun-orientation for solar-power accumulation is disclosed. Momentum-bias both maintains nadir pointing and adds yaw-steering moments for sun-trackig attitude control, simultaneously. The method has two principal steps: 1) open-loop momentum decoupling, for correcting the calculated steering torque, and closed-loop attitude compensation, to correct for perturbations about the calculated attitude in accordance with one of two control law definitions. This combines the advantage of stable gyroscopic attitude control with those of open-loop yaw steering.

Abstract: The apparatus is an earth horizon crossing indicator used in a spacecraft attitude control system, which uses power from a self-contained battery rather than power from the spacecraft electrical system. The battery is typically of the lithium thionyl chloride type. This reduces the weight and complexity of the spacecraft attitude control system and allows the resources of the spacecraft electrical system to be used for other devices.

Abstract: The earth horizon sensor apparatus uses first and second linear sensor arrays of sensor elements, the first and second linear sensor arrays being staggered with respect to each other. The sensor elements are preferably pyroelectric elements for detecting the presence or absence of infrared radiation from the Earth and Space. A microprocessor is used to determine which of the sensor elements subtends the diffuse horizon gradient and the constant zero radiance of Space. The attitude of the spacecraft is thereby calculated.