Abstract: A method, apparatus, article of manufacture for determining the attitude of a spacecraft having at least one star sensor. The method comprises the steps of selecting a first reference star sensor from among the star sensors; designating two stars observed by the first reference star sensor as a primary star pair; identifying a candidate star pair corresponding to the primary star pair, wherein the candidate star pair is selected from a star catalog having a plurality of entries; estimating an inertial orientation of the first star sensor at least in part from the identified candidate star pair; and determining the spacecraft attitude from the estimated inertial orientation of a reference star sensor selected from a group comprising the first star sensor.

Abstract: A method, computer system, and program product for optimizing a useful objective function with respect to a dynamic parameter vector and a static parameter vector. The method, called the static/dynamic control (MDC) method, either minimizes or maximizes the useful objective function subject to a state equation, initial conditions, terminal conditions, constraints, and dynamic limitations. The SDC method includes an algorithm having two formulations: a period formulation and a fully continuous formulation. With the period formulation, the dynamic optimization variables associated with the dynamic limitations are permitted to be discontinuous, parametric functions of time. With the fully continuous formulation, the dynamic optimization variables are permitted to be continuous, non-parametric functions of time. The SDC method is computer implementable and employs an iterative process including an inner loop and an outer loop.

Abstract: Described is a device for determining the attitude on board of a satellite (1) with a data transfer device for carrying out optical data exchange between at least two satellites (1, 3); a device for determining one's own attitude; a device for determining the directional vectors in an inertial co-ordinate system from one's own attitude and from attitude data of at least two satellites (1, 3), said attitude data having been transmitted by means of the data transmission device; a device for determining the directional vector directed to the satellites (1, 3) of which there are at least two, in a fixed-body co-ordinate system of the satellite; and a device for attitude determination from the directional vectors determined. Also described is a method for carrying out attitude determination.

Abstract: A spacecraft includes an articulating sunshield assembly that is capable of simultaneously performing thermal control functions and solar torque balancing for the spacecraft. The sunshield assembly includes a pair of shield members that can be controllably positioned as the spacecraft orbits about a primary body. Control functionality is provided for periodically adjusting the positions of the shield members to maintain a neutral solar torque stability condition for the spacecraft. In one embodiment, solar torque balancing is performed in each of three independent rotational directions or planes (i.e., roll, pitch, and yaw) using the sunshield assembly. Functionality is also provided for performing momentum dumping tasks using the sunshield assembly in place of, or in conjunction with, on-board thrusters.

Abstract: An attitude control system comprising a controller and a noise screen device coupled to the controller. The controller is adapted to control an attitude of a vehicle carrying an actuator system that is adapted to pulse in metered bursts in order to generate a control torque to control the attitude of the vehicle in response to a control pulse. The noise screen device is adapted to generate a noise screen signal in response to the control pulse that is generated when an input attitude error signal exceeds a predetermined deadband attitude level. The noise screen signal comprises a decaying offset signal that when combined with the attitude error input signal results in a net attitude error input signal away from the predetermined deadband level to reduce further control pulse generation.

Abstract: An improved satellite system that limits or eliminates the dynamical rotational response of a satellite body to solar array asymmetrical and symmetrical flexing. The improvement is made by rotating one of a pair of solar arrays to an angle relative to the other solar array along a satellite pitch axis. The solar arrays are then rotated to a position wherein a maximum surface area of solar panels located on the pair of solar arrays is exposed to direct sunlight. The improvement enhances the ability of the satellite to maintain high precision angular stability under operational disturbances without costly and complex structural stiffening solutions.

Abstract: An attitude control system uses a first order partial derivative of an error signal, representing a difference between a commanded pitch attitude and a sensed, actual pitch attitude. The first order partial derivative forms a cross product with the Earth's magnetic field to provide a X axis torque rod dipole command, which powers the torque rod in a way that causes a satellite to move toward its commanded attitude.

Abstract: A system (30) for adjusting the orientation of a spacecraft adapted for use with a satellite (10). The system (30) includes a first control circuit (32, 38, 40) for canceling any momentum of the spacecraft via a counter-rotating spacecraft bus (16, 18). A second controller (32, 42, 44, 46, 48) orients the spacecraft via the application of internal spacecraft forces. In a specific embodiment, the spacecraft bus (16, 18) serves a dual use as storage section and includes a mass (16) having a moment of inertia on the same order as the moment of inertia of the satellite (10). The satellite (10) includes a bus section (16) and a payload section (14). The mass (16) includes the bus section (16). The first control circuit (32, 38, 40) runs software to selectively spin the mass (16) to cancel the momentum of the satellite (10). The software computes an actuator control signal, via a computer (32), that drives a first actuator (38) that spins the mass (16).

Abstract: This invention provides an offline attitude determining apparatus capable of detecting an artificial satellite attitude at a high precision in wide band. Averaging and addition processing are carried out on a low-frequency attitude interpolation signal generated by interpolating a low-frequency attitude detection signal obtained by inputting an attitude angle determination signal generated by a sequential Kalman filter computation device and a high-frequency attitude detection signal obtained by inputting a high-frequency attitude angle sensor detection signal extracted by a high-frequency attitude angle sensor data extracting device into a band pass filter computation device, so as to generate a high-precision attitude detection signal. By combining the low-frequency attitude detection signal with the high-frequency attitude detection signal with an interpolation processing computation device and an attitude data generator, the attitude can be determined at a high precision in wide band.

Abstract: In a method for maintaining the orbital position of a geostationary satellite by compensating perturbational effects of interfering influences, a range of the satellite orbit is determined, relative to a space-fixed reference system, in which the perturbational effects on the satellite position by the interfering influences reaches a maximum. Position maintaining actuators of the satellite are activated within the determined range.

Abstract: An integrated system for providing 3-axis attitude-control, energy-storage, and electrical power in which two counter-rotating inertia-wheels are tandem mounted with rotational axis oriented on and parallel to the longitudinal-axis of an airframe. A horizontal- and vertical-translating support is centrally-located between the wheels and houses a common wheel-bearing mount communicating with and supporting both inward-pointing inertia-wheel shafts. The preferred embodiment further consists of two outwardly-mounted tilt wheel bearing and suspension means, each communicating with and supporting an inertia-wheel outward-pointing shaft. Taken together, these supports and their associated two-axis actuator enable both wheels to be tilted equally in opposite directions to generate a combination of pitch and yaw reaction torque. Further, an electric generator integrally mounted to each inertia-wheel, and an electric load controller connected to each electric generator enable the creation of reaction roll torque.

Abstract: A control system for providing attitude control in spacecraft. The control system comprising a primary attitude reference system, a secondary attitude reference system, and a hyper-complex number differencing system. The hyper-complex number differencing system is connectable to the primary attitude reference system and the secondary attitude reference system.

Abstract: A controller and control method that perform satellite orbit-keeping maneuvers and proportionally scale orbit-keeping pulses to automatically minimize disturbance torques on-board a satellite. The controller and control method may also be used to remove residual momentum stored in spinning momentum wheels.

Abstract: An automatic, on-board system for orbiting spacecraft that controls and reduces short-term transients caused by roll momentum unloads by manipulating the states of the nutation damper through resetting one of the states in the polynomial transfer function to a value in proportion to the magnitude of the expected roll momentum unload and creating a transient equal and opposite in magnitude to that expected by the roll unload. The compensator will, of its own accord, automatically damp out the resulting transient. Thus the short-term transient is reduced without biasing the spacecraft in roll. No angle bias need be changed or removed.

Abstract: A method, apparatus, and article of manufacture for directing a payload coupled to a spacecraft substantially at a target location is disclosed. The method comprises the steps of determining spacecraft orbital parameters and spacecraft payload attitude parameters; and directing the payload at the target location by applying a spacecraft bus steering law determined at least in part from the orbit and attitude parameters. The apparatus comprises a navigation system for determining spacecraft orbit parameters and spacecraft attitude parameters, and for applying a spacecraft bus steering law to direct the payload substantially at the target location. The spacecraft bus steering law is determined at least in part from the determined spacecraft orbital parameters, the determined spacecraft attitude, and determined payload attitude parameters. In one embodiment, the apparatus includes a payload attitude control system for directing the payload relative to the spacecraft bus.

Abstract: A system for managing electrical energy and for controlling attitide of a satellite has an attitude control unit which controls a plurality of reaction wheels oriented about different axes for instance three wheels. An on-board electricity power supply network has a solar array, a payload and a storage unit connected to a power line. The storage unit comprises a buffer supercapacitor and one inertia wheel unit with a respective motor/generator and typically two contra-rotating wheels. Interchanges between the storage units and the power supply line are controlled by a regulator which attenuates power demand transients and thus torque transients on the inertia wheel or wheels.

Abstract: The attitude of a tiltable body is tracked and controlled on the basis of signals outputted from gyros and tilt sensors. The signals outputted from the gyros are transformed and integrated to produce estimated position information in the form of a modified quaternion in which the yaw component is constrained to a zero value. Modified quaternion information in the same form is also generated from signals outputted from the tilt sensor and is used to detect and correct an error component in the estimated position information. Gyro drift is also corrected based on the output of the tilt sensor.

Abstract: Orientation system and process of an artificial satellite in low orbit. Aerodynamic control surfaces producing rotations of the satellite by upper-layer atmosphere are combined along two axes to magnetic couplers (1, 2, 3) producing rotating movements along the three principal axes of pitch, roll and yaw thanks to the Earth's magnetic field. Great precision may be obtained in orienting the satellite without substantial energy consumption. Command laws are provided.

Abstract: A magnetic torquer (10) for spacecraft attitude control, providing a torque that is controllable over an extended range greater than a normally used linear range, and thereby providing a higher ratio of maximum torque to device weight. In one form of the torquer, a feedback loop including a sensor (20), a signal subtraction circuit (24), a controller (28) and an adjustable power supply (16), continuously determines a corrected command signal that results in the generation of a desired magnetic moment and a corresponding torque, over the extended range, regardless of non-linearity across the extended range. In an alternate form of the torquer, the corrected command signal is generated from a mathematical model (56) of the magnetic torquer (10). Use of the invention also minimizes the effect of any residual magnetic moment that might by present when the actuating current is reduced to zero.

Abstract: Stellar attitude-control systems and methods are provided with enhanced accuracy because they recognize that important star tracker errors exhibit a boresight symmetry and that these errors can be accurately defined by weighting a measurement-noise covariance matrix R(tn) with variances that are functions of off-boresight angles of detected stars. A method of the invention derives off-boresight angles &thgr; from star-tracker signals of detected stars. These off-boresight angles &thgr; are combined with variance coefficients &agr; to generate off-boresight variances rob(tn) that are functions of the off-boresight angles &thgr; and, in particular, correspond to star tracker color shift errors. A gain matrix K(tn) is then calculated with a weighted measurement-noise covariance matrix R(tn) that includes the off-boresight variances rob(tn). This gain matrix is used to generate an attitude estimate matrix X*(tn) for use in spacecraft attitude control.

Abstract: A spacecraft orbit control system and method for controlling the orbit of a spacecraft during orbit raising includes processing spacecraft position data to meet the spacecraft attitude sensing needs for long duration, low thrust orbit raising bums. The actual spacecraft position as determined by a global positioning system (GPS) receiver is compared with the desired spacecraft position to generate an error signal indicative of a spacecraft position error for adjusting the attitude of the spacecraft as thrusters move the spacecraft. The attitude of the spacecraft is adjusted to eliminate the spacecraft position error such that the actual spacecraft position corresponds with the desired spacecraft position and the spacecraft maintains a desired orbit during the orbit raising.

Abstract: A method, apparatus, article of manufacture, and a memory structure for controlling an attitude and a nutation of a spacecraft spinning about a first axis. The method comprises the steps of measuring a spacecraft attitude rate &ohgr;1(t) about a second axis substantially orthogonal to the first axis; generating a rate correction value &agr;&ohgr;1(t)/&lgr;0, wherein &lgr;0 is an inertial nutation frequency of the spinning spacecraft, and &agr; is a proportionality factor; determining a spacecraft attitude angle &phgr;2(t) about a third axis substantially orthogonal to the first axis and the second axis; generating an error signal e(t) as &phgr;2(t)+&agr;&ohgr;1(t)/&lgr;0; and applying a torque to rotate the spacecraft along the second axis. The article of manufacture comprises a program storage device storing instructions implementing the instructions described above.

Abstract: A microaltimeter measures altitude or range highly accurately from an orbiting vehicle. The microaltimeter has a low power solid state laser that is pulsed at a rate above 1 kilohertz. The pulses are delivered to a small telescope which sends them to a planetary surface and receives return reflections. A high efficiency photon detector measures received photons and supplies received photon signals to a process or which makes a time-based bin-wise comparison to find the time of flight and hence the range.

Abstract: A moment control device for positioning a spacecraft which employs a plurality of spinning bodies operable to impart a desired torque to a space craft, the bodies being constructed in a unitary combination and the unitary combination being mounted to the spacecraft to be positioned.

Abstract: An apparatus and method of unified orbit and attitude control for acquisition and maintenance techniques of multiple satellites in a formation based on GPS input, utilizing Modern Feedback Control for providing precise autonomous on-board orbit and attitude control. This control system can place and maintain any satellite in its designated location in a formation, while simultaneously providing the capability to attain and maintain the attitude of any of the satellites in the formation with respect to the reference ‘head-of-fleet’ satellite.

Abstract: A method, apparatus, article of manufacture, and a memory structure for compensating for instrument induced spacecraft jitter is disclosed. The apparatus comprises a spacecraft control processor for producing an actuator command signal, a signal generator, for producing a cancellation signal having at least one harmonic having a frequency and an amplitude substantially equal to that of a disturbance harmonic interacting with a spacecraft structural resonance and a phase substantially out of phase with the disturbance harmonic interacting with the spacecraft structural resonance, and at least one spacecraft control actuator, communicatively coupled to the spacecraft control processor and the signal generator for inducing satellite motion according to the actuator command signal and the cancellation signal.

Abstract: A method of velocity precision pointing of spin-stabilized spacecraft or rockets is disclosed.

Abstract: Apparatus and methods for performing satellite proximity operations such as inspection, recovery and life extension of a target satellite through operation of a “Satellite Inspection Recovery and Extension” (“SIRE”) spacecraft which can be operated in the following modes (teleoperated, automatic, and autonomous). The SIRE concept further consists of those methods and techniques used to perform certain (on-orbit) operations including, but not limited to, the inspection, servicing, recovery, and lifetime extension of satellites, spacecraft, space systems, space platforms, and other vehicles and objects in space, collectively defined as “target satellites”. The three basic types of SIRE proximity missions are defined as “Lifetime Extension”, “Recovery”, and “Utility”. A remote cockpit system is provided to permit human control of the SIRE spacecraft during proximity operations.

Abstract: An apparatus for star catalog equalization to enhance attitude determination includes a star tracker, a star catalog and a controller. The star tracker is used to sense the positions of stars and generate signals corresponding to the positions of the stars as seen in its field of view. The star catalog contains star location data that is stored using a primary and multiple secondary arrays sorted by both declination (DEC) and right ascension (RA), respectively. The star location data stored in the star catalog is predetermined by calculating a plurality of desired star locations, associating one of a plurality of stars with each of the plurality of desired star locations based upon a neighborhood association angle to generate an associated plurality of star locations: If an artificial star gap occurs during association, then the neighborhood association angle for reassociation is increased.

Abstract: A method, apparatus, article of manufacture for compensating for solar wing thermal shock in a spacecraft. The method comprises the steps of determining solar wing compensation to compensate for the thermal shock disturbance and rotating the solar wing about a second axis according to the determined compensation, wherein the second axis is substantially perpendicular to the first axis and to a vector from the spacecraft to the sun. The solar wing compensation can be based on predicted solar wing deflections due to thermal shock perturbations, or if available, solar wing temperature measurements. In an embodiment of the present invention applicable to satellites with multiple solar wings, asymmetric control is applied by independent adjustment of the thermal shock compensation loop controlling each solar wing. In yet another embodiment of the present invention, the solar wing position actuator is further commanded by a feedback control loop using the measured spacecraft attitude.

Abstract: A method of injecting a missile, having a solid fuel motor, into a satellite orbit. The method includes determining an along-track displacement and cross-track displacement with respect to the satellite orbit. The method also includes determining a velocity-to-be-gained for the satellite orbit, with respect to the current missile velocity. Along-track and cross-track wasting of the solid fuel motor are used to reach the satellite orbit, at the proper velocity for the satellite orbit, when the solid fuel motor burns out.

Abstract: A method for use on a satellite that automatically inhibits scanning of an Earth sensor to handle sensor intrusions by the sun, moon, or other celestial bodies. In implementing the method, a predicted state vector for the satellite, derived from an orbit propagator, is generated. An attitude profile for the satellite is generated. Then, the satellite state (predicted state vector) and attitude profile are processed to determine Earth, sun, and moon vectors in a satellite body frame of reference at any instant. The Earth, sun, and moon vectors are compared to the Earth sensor field of view and sensor field of view limit boxes to determine if scan inhibiting or Earth sensor switching should occur. The affected Earth sensor is inhibited or switched if an intrusion of the sun and/or moon into the field of view of the Earth sensor is predicted.

Abstract: A method of controlling the orbit of an inclined, eccentric geosynchronous satellite by maintaining its perigee location while simultaneously preventing a reference point on the orbit from moving too far relative to a normal position over the Earth. Doing this changes the semimajor axis of the orbit, which when perturbed away from the geosynchronous value, creates a drift rate relative to the Earth. To correct the argument of perigee and maintain the prescribed tolerance on ground track position, multiple maneuvers must be performed to control the drift rate. The relationship between maximum allowable velocity change and time between maneuvers is defined by the required correction to the argument of perigee and the allowable motion of the reference point.

Abstract: A method and apparatus for controlling a spacecraft having a first axis is disclosed. The apparatus comprises a momentum wheel unidirectionally rotatable about a spin axis substantially co-aligned with the first axis; a momentum wheel mount for tilting the momentum wheel about at least one of two axes substantially orthogonal to the spin axis; and a processor in communication with the momentum wheel and the momentum wheel mount. The processor commands either the momentum wheel speed or the momentum wheel tilting to control the attitude of the spacecraft in a first orientation and in a second orientation inverted from the first along the first axis, using the same control law.

Abstract: A spacecraft having a body, one or more appendages coupled thereto, and a controller that implements methods that rotate the one or more flexible appendages to point it (them) towards the Sun to reduce spacecraft attitude pointing disturbances and improves spacecraft attitude pointing. The steps of the one or more appendages are timed to deadbeat the disturbance imparted to the spacecraft body. Timing of the appendage steps may be such that the periodic disturbances are phased to substantially cancel each other, or phased to decrease the magnitude of the net disturbance. The present invention also cancels solar array slew disturbances. The present invention cancels predictable disturbance torques before they produce a pointing error, improving the spacecraft pointing performance.

Abstract: A system and method of estimating the attitude of a spacecraft is disclosed. A three-axis inertial-based estimate of spacecraft attitude is produced and is compared to a stellar-based estimate of spacecraft attitude. A Kalman filter having states associated with gyro scale factor and/or misalignment errors compares the stellar-based attitude estimate to the inertial-based estimate of attitude and apportions the total error into three time varying matrices. A first time varying matrix is associated with gyro scale factor and misalignment errors, a second time varying matrix is associated with gyro bias errors, and a third time varying matrix is associated with attitude errors. The time varying matrices are applied as corrective feedbacks to the inertial-based estimate of spacecraft attitude and are adaptively adjusted to minimize the error therein.

Abstract: A momentum control system for driving the momentum of a spinning spacecraft to zero while it spins around a sunline. The system includes a sun sensor for determining the position of the sun, a suite of tachometers for determining the momentum stored in the spacecraft, and a stored movement sensor. Each of the readings from these sensors is fed to a controller. The controller also monitors the magnitude of the spacecraft overturning momentum and the windmill momentum. If the overturning momentum is outside acceptable limits then the rotation rate of the spacecraft is modulated to drive the overturning momentum towards zero. If the windmill momentum exceeds acceptable limits, the angle of the solar panel is adjusted to drive the windmill momentum towards zero.

Abstract: A satellite (30) programmed for sun-nadir steering and having a solar wing (36) mounted to the satellite body (35) and being selectively moveable about two mutually orthogonal axes (A, B). The solar wing (36) is mounted to the satellite body (35) by a pair of gimbals (43, 45) thus allowing two degrees of freedom and thereby permitting the solar wing (36) to be rotated about the two mutually orthogonal axes (A, B). A first motor (42) in operative engagement with the gimbal (43) selectively rotates the solar wing about the axis (A), while a second motor (46) in operative engagement with the gimbal (45) selectively rotates the solar wing about the second axis (B). A control circuit (40) is in operative engagement with the first and second motors and selectively causes the first motor to rotate the solar wing about the first axis to a predetermined position, and selectively causes the second motor to rotate the solar wing about the second axis to a predetermined position.

Abstract: Control systems and methods are provided which enhance acquisition range, transient response and offset pointing accuracy in beacon-assisted orientation of a spacecraft to a desired spacecraft attitude Adsrd. The methods receive a beacon signal with antennas that are arranged in a fixed angular relationship to thereby form an attitude error signal Serr whose magnitude is a measure of the attitude difference between a current spacecraft attitude Acrnt and the desired spacecraft attitude Adsrd. A sum power P&Sgr; that is the sum of the signal powers from the antennas is sensed and a signal modifier Smod is generated that increases with decreases in the sum power P&Sgr;. The attitude error signal Serr is then modified with a term (1+Smod) to form an enhanced attitude error signal Serrenhd. In one embodiment, the signal modifier Smod is n|Pmax−P&Sgr;|m wherein n and m are positive numbers and Pmax is the sum power P&Sgr; when the attitude error is zero.

Abstract: A star tracker coupled to the spacecraft having a star catalog associated therewith. A sun sensor is coupled to the spacecraft. A control processor is coupled to the star tracker and the sun sensor. The processor obtains star data using a star tracker and an on-board star catalog. The processor generates a coarse attitude of the spacecraft as a function of the star data, and establishes a track on at least one star in the on-board star catalog. The processor calculates a sun tracking rate, and obtains a normal phase attitude as a function of the star data and the coarse attitude. The information is used to slew the spacecraft to a desired attitude.

Abstract: For an antenna on a satellite in an inclined orbit about the Earth, cross-track motion resulting from the rotation of the Earth can be reduced in antenna coordinates by yawing the antenna (preferably by yawing the entire satellite, for example, by using a reaction wheel system) by an appropriate angle, which varies throughout the orbit.

Abstract: A method and system for minimizing attitude errors resulting from dynamic spacecraft maneuvers or time-varying mismatched attitude sensor measurements. The method includes time-tagging a primary attitude value from a primary attitude sensor and storing the value and associated time stamp in a buffer. A secondary attitude value, generated by a secondary attitude sensor, having a different associated time-stamp is then time-matched to the primary attitude valve. The corrected spacecraft attitude is then calculated as a function of the time-matched primary and secondary attitude values. In one aspect of the invention, the primary attitude sensor generates attitude data at a faster rate than the secondary attitude sensor. This primary attitude data is stored in a buffer such that, when the secondary attitude data becomes available, several nearest-in-time primary attitude data points are retrieved from the buffer. These data points are then used to interpolate a higher time-matched resolution data point.

Abstract: A system and method for determining the attitude in an inertial frame of a spacecraft spinning about an axis in a body frame including determining momentum vector direction in the inertial frame; determining momentum vector direction in the body frame; acquiring information from an at least single-axis sensor; obtaining reference information on the at least single-axis sensor; updating the attitude in the inertial reference frame using the momentum vector direction in the inertial frame, the momentum vector direction in the body frame, the output of the at least single-axis sensor, and the reference information on the at least single-axis sensor; and propagating the attitude using data from one or more inertial sensors.

Abstract: A smart docking surface consisting of closely spaced cantilevered sensor/actuator structures capable of precisely repositioning an object having a ferro-magnetic surface in contact with the smart docking surface. It is designed for use in a micro gravity environment for the final docking sequence of two small (<100 kg) satellites. Its purpose is to reduce the complexity of the docking process where a precise mating is required.

Abstract: A receiver clock bias signal for a spacecraft in motion is is used to obtain a real-time navigation Kalman filter solution of the clock bias and provide a robust autonomous GPS time reference, even when there are less than 4 GPS satellites within the view of the receiver in the spacecraft. The Kalman filter of the spacecraft provides an accurate solution of the clock bias, with less than 4 GPS satellite signals, by means of a system which uses the knowledge of the dynamic motion of the satellite in conjunction with GPS signals for a robust estimation of time. The system provides an accurate GPS time reference by transferring timing information from an atomic reference standard (GPS) to a spacecraft in motion by directly measuring the GPS signal and without depending upon the tracking of multiple GPS satellites or a static receiver. Implementation in current aerospace qualified GPS receivers, e.g.

Abstract: The attitude of a spacecraft is controlled during an eclipse without the dependence on auxiliary power by configuring the spacecraft so that it will receive solar power after solar eclipse is passed. The spacecraft is then oriented with respect to a sun line. The spacecraft is then spun so that it maintains a desired angular momentum throughout the eclipse and provides passive stabilization of the attitude. After the eclipse has passed, the spacecraft power is restored and the spacecraft attitude is detected. All spacecraft units are then powered up and thereafter, normal on-station attitude is re-established and normal spacecraft operations are established.

Abstract: A method is provided for controlling the attitude of a momentum biased spacecraft about all three mutually orthogonal axes during a thruster firing maneuver without separately sensing angular displacement, angular rate, or angular acceleration about the spacecraft yaw axis. The method includes a transient phase during which a yaw feedforward torque is computed based on the known pitch/yaw coupling due to thruster geometry, and a steady state phase, during which feedback gains are adjusted to estimate yaw attitude based on coupling of a steady state disturbance torque about the roll axis of the spacecraft and a steady state disturbance torque about the yaw axis of the spacecraft.

Abstract: A method and apparatus are provided that effect spacecraft wheel desaturation by controlling the magnetic torquers aboard the spacecraft. An attitude control system energizes a magnetic torquer coil or set of magnetic torquer coils using a power source having an initial polarity and then monitors the spacecraft's response to the torque created by the coil's magnetic field. By measuring the spacecraft's response to the torque created by the energized magnetic torquers, the direction of the earth's magnetic field is determined. Once the direction of the earth's magnetic field is known, the proper polarity may be applied to the coil to achieve the desired torque. The control system of the present invention synchronously demodulates the craft's angular velocity, estimated from signals obtained from the attitude sensors, using a small dither signal that is superimposed on the control current used to energize the magnetic torquer coil.

Abstract: An earth observation system capable of observing the earth globally and uniformly in a steady observation operation mode while observing a given district on the earth in a high-frequency observation operation mode, as occasion requires, includes a plurality of observation satellites each equipped with an orbit transfer facility, an observation data receiving system, an observation satellite operating ground system, an observation command facility such as anti-disaster task forces, institutes or the like. In the steady observation operation mode for observing globally the earth, M observation satellites are constellated on each of L sun-synchronized quasi-recurrent orbits each having a same altitude and a same inclination (where L and M represents natural numbers). In the high-frequency observation operation mode for observing a particular district on the earth, M satellites are constellated on each of L sun-synchronized recurrent orbits each having a nominal altitude of 561 km and a nominal inclination 97.

Abstract: Satellite attitude control methods for use during orbit raising operations to follow a predefined thrust trajectory that meets geometric constraints imposed by sensor and/or telemetry and control antenna fields of view while optimizing the sun angle on the solar array. The method uses low thrust electric propulsion for geosynchronous satellite orbit raising from a transfer orbit to the final geosynchronous orbit. In implementing the methods, a predefined thrust trajectory is generated that is designed to raise a satellite from a transfer orbit to a geosynchronous orbit. A direction-cosines matrix, or quaternion, is generated that aligns a thrust vector defined in the satellite body frame with the predefined thrust trajectory and rotates the satellite body about that vector.