Abstract: In detail, the system includes at least one first pulley mounted on the first structural member and at least one-second pulley mounted on the second structural member. A cable is attached by one end to the first structural member and wound about the first and second pulleys and is attached by its second end to the second structural member. Preferably there are two or more first and second pulleys with the cable alternately wound between said first and second pulleys with one end of cable attached to the first structural member and the opposite end attached to the second structural member. Thus the cable holds the first and second structural members together. A system to sever the cable is included, which upon actuation will sever the cable allowing the two structural members to separate.

Abstract: A spacecraft orbit control system and method that provides orbit control of a spacecraft. The system comprises the spacecraft, one or more electric and/or chemical thrusters disposed on the spacecraft, and a control processor having control outputs coupled to the plurality of thrusters. An orbit control algorithm is implemented that determines the current orbit of the spacecraft, determines whether or not to perform stationkeeping, determines desired changes in certain orbit parameters if stationkeeping is to be performed, determines thruster firings that accomplish the desired orbit parameter changes, and fires the thrusters to perform spacecraft stationkeeping and provide spacecraft longitude control. The present invention may be used with any type of orbit determination procedure (such as GPS or ranging, with or without orbit propagation) and any type of stationkeeping algorithm that calculates thruster firings from desired orbit-parameter corrections.

Abstract: Spacecraft thruster systems are provided that can realize station changing, station keeping and momentum dumping in spacecraft while minimizing loss of spacecraft service time. The systems are formed with pairs of E and W thrusters, NE and SE thrusters and NW and SW thrusters whose thrust directions are each defined by respective polar angles &phgr; and slew angles &agr;. The E and W thrusters are especially suited for rapid station changing while the remaining thrusters generate normal, tangential and radial thrust components required for station keeping. Because all thrusters are directed through the spacecraft's center of mass during station changing and station keeping firings, the spacecraft's attitude is not disturbed and loss of service time is avoided. The thrusters are preferably gimbaled so that they can track spatial changes of the spacecraft's center of mass or, for momentum dumping, be offset from that center of mass.

Abstract: A microelectrical mechanical system (MEMS) microthruster array is disclosed. The MEMS microthruster array of the present invention can be used for maintaining inter satellite distance in small satellites. One microthruster array includes numerous microthruster propulsion cells, each having a vacuum enclosed explosive igniter disposed on one side by a breakable diaphragm and having a propellant-filled chamber on the opposite side of the diaphragm. Upon explosion of the explosive igniter, the first diaphragm breaks, which, together with the explosion of the explosive igniter, causes the propellant to expand rapidly, thereby providing exhaust gases which are ejected from an exterior face of the microthruster propulsion array, thereby providing a small unit of thrust.

Abstract: Various types of valves are disclosed, as well as the use of the same in a reaction control system for space travel vehicle applications. Multiple functions are provided by one of these valve designs by providing multiple flowpaths through the valve. An inflow and outflow tube of this multifunctional valve are fluidly interconnected with first and second chambers, respectively, within the valve. These first and second chambers are isolated from each other by a barrier assembly which may be “removed” at the desired type by a barrier rupture assembly to provide one of the noted multiple flowpaths (i.e., the inflow tube, the first chamber, the second chamber, and the outflow tube). A separate service port is fluidly interconnected with each of the first and second chambers, and a separate service valve may be disposed in each of these service ports to provide additional flowpaths for the multifunctional valve.

Abstract: A Stationkeeping Mode for a spacecraft having a gimballed momentum wheel for attitude control in which the stationkeeping is divided into short duration open-loop stationkeeping maneuvers to correct orbital errors, and interlaced with closed-loop momentum management operations to manage momentum stored in the momentum wheel. The sequence of open-loop pulses are spaced to deadbeat a given dominant flexible motion of the spacecraft. Between and during the thruster pulses, the gimbaled momentum wheel is maintained in the closed-loop feedback control using gyro sensor or other inertial reference measurements. Limitations on the range of the momentum storage device and its torque capability are minimized by combining the maneuver thruster pulses with pulses from other thrusters, or by reducing the fire time of one of the maneuver thrusters, to minimize momentum buildup.

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 integrated system for missile steering, which uses both jet reaction control (JRC) and aerofin control systems, is provided with a variable coupling mechanism for adjusting the relative responsiveness of the two systems in accordance with the pressurization state of the JRC system pressure chamber. In one embodiment, the pivoting action of a joystick which actuates the gas flow control pintles of the JRC system is permitted only under sufficient pressurization of the pressure chamber. In a second embodiment, the extent to which the pintles protrude from their controllable housings is adjusted according to the pressure in the pressure chamber. In this manner, when JRC is undesirable or is unavailable, the missile aerofins are permitted their full range of motion without being constrained by the pintles.

Abstract: A reduced toxicity fuel satellite propulsion system including a reduced toxicity propellant supply (10) for consumption in an axial class thruster (14) and an ACS class thruster (16). The system includes suitable valves and conduits (22) for supplying the reduced toxicity propellant to the ACS decomposing element (26) of an ACS thruster. The ACS decomposing element is operative to decompose the reduced toxicity propellant into hot propulsive gases. In addition the system includes suitable valves and conduits (18) for supplying the reduced toxicity propellant to an axial decomposing element (24) of the axial thruster. The axial decomposing element is operative to decompose the reduced toxicity propellant into hot gases. The system firther includes suitable valves and conduits (20) for supplying a second propellant (12) to a combustion chamber (28) of the axial thruster, whereby the hot gases and the second propellant auto-ignite and begin the combustion process for producing thrust.

Abstract: There is provided a method and system for simultaneous north-south stationkeeping and 3-axis momentum management for a geosynchronous orbiting spacecraft. The spacecraft has a first thruster, a second thruster, and at least three momentum wheels mounted on-board the spacecraft. The first and second thrusters are mounted adjacent to a north and a south face of the spacecraft, respectively, on an anti-earth side of the spacecraft and are aligned to produce thrust vectors slightly off from the spacecraft's center of mass. The first and second thrusters are independently fired at predetermined positions along the geosynchronous orbital path of the spacecraft. The thrust vectors provide attitude and orbital adjustment needed to correct north-south orbital position deviation and provide torque needed to desaturate the stored angular momentum of the momentum wheels.

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 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: An attitude control system and method operative with a thruster controls the attitude of a vehicle carrying the thruster, wherein the thruster has a valve enabling the formation of pulses of expelled gas from a source of compressed gas. Data of the attitude of the vehicle is gathered, wherein the vehicle is located within a force field tending to orient the vehicle in a first attitude different from a desired attitude. The attitude data is evaluated to determine a pattern of values of attitude of the vehicle in response to the gas pulses of the thruster and in response to the force field. The system and the method maintain the attitude within a predetermined band of values of attitude which includes the desired attitude. Computation circuitry establishes an optimal duration of each of the gas pulses based on the pattern of values of attitude, the optimal duration providing for a minimal number of opening and closure operations of the valve.

Abstract: A spacecraft attitude and altitude control system utilizes sets of three pulsed plasma thrusters connected to a single controller. The single controller controls the operation of each thruster in the set. The control of a set of three thrusters in the set makes it possible to provide a component of thrust along any one of three desired axes. This configuration reduces the total weight of a spacecraft since only one controller and its associated electronics is required for each set of thrusters rather than a controller for each thruster. The thrusters are positioned about the spacecraft such that the effect of the thrusters is balanced.

Abstract: Controlled momentum gyros are rotated to change the attitude of a satellite as rapidly as possible by rotating them along a great circle path on an imaginary spherical surface around the satellite. Adjustments the gyro rotations are made in two directions, along the spherical surface, as the satellite rotates. All the stored angular momentum in the gyros is used to rotate the satellite, rather than limiting the rotation of the gyros to avoid instabilities from singularities in traditional control laws.

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 neural network controller for a pulsed rocket motor tactical missile. The missile includes a fuselage or body, with a propulsion system. The pulsed propulsion system has a need for a logical control of the application of propulsion energy throughout the missile's flight. The controller is trained to provide optimal initiation of individual rocket motor thrust pulses based on tactical information available at various points/times in the missile's flight. The controller training is through use of training cases, in which the network learns to output a specific target value(s) when specific values are input. When trained with a large sample of training cases selected from the multidimensional population of interest, the neural network effectively learns the correlations between inputs and outputs and can predict input/output relationships not previously seen in any training case.

Abstract: A practical stationkeeping method and apparatus wherein an electric propulsion system on a satellite is used to correct north-south drift and the majority of east-west drift which is caused by orbital eccentricity growth. A chemical propulsion system on the satellite is used to correct the remainder of east-west drift due to the growth of orbital semimajor axis. The method and apparatus eliminate the need for additional electric thruster burns in case of an electric thruster failure and therefore eliminates associated power and mass penalties.

Abstract: A rocket propulsion system for spacecraft achieves greater economy, reliability and efficiency rocket by incorporating monopropellant RCS thrusters (1a-1f) for attitude control and bipropellant SCAT thrusters (5a-5c) for velocity control. Both sets of thrusters are designed to use the same liquid fuel, supplied by a pressurized non-pressure regulated tank, and operate in the blow down mode. In the propulsion system such station keeping and attitude control thrusters may function in conjunction with a large thrust apogee kick engine, which may also be of the SCAT thruster construction, that uses the same propellent fuel. Hydrazine and Binitrogen tetroxide are preferred as the fuel and oxidizer, respectively. The new system offers a simple conversion of existing monopropellant systems to a high performance bipropellant dual mode system without the extreme complexity and cost attendant to a binitrogen tetroxide--hydrazine bipropellant system.

Abstract: A compact single-propellant unitary propulsion system for placing a satellite into an orbit and subsequently correcting the orbit so that the satellite is stabilized on three axes comprises a liquid propellant tank secured to a satellite platform and having a reinforced bottom wall with an outlet and filter element, a distribution block welded to the reinforced bottom wall, at least one filling/emptying value mounted on the distribution block, and a set of at least two thrusters mounted on the distribution block and fed directly from the distribution block without additional pipework. The set of at least two thrusters point substantially along the axis of the tank, which is aligned with the axis of the satellite. The propulsion system may be fully assembled before it is integrated with the satellite.

Abstract: Control moment gyros in an array are rotated to reorient a satellite. Gyro angle is selected from one of three values based upon whether the stored angular momentum for the desired angle is below a singularity free value, greater than the singularity free value or is greater than the maximum available stored angular momentum.

Abstract: A spacecraft according to the invention includes a pair of propellant tanks, with the nominal center of mass of the spacecraft located therebetween. Propellant is coupled from the tanks to a velocity-change-inducing thruster by a controllable coupling arrangement. Unwanted torques may occur which tend to perturb the attitude. An attitude control arrangement generates an error signal in response to deviations of the attitude from the desired attitude. The error signal is processed to control the propellant coupling arrangement, to cause propellant to be used preferentially from at least one of the tanks in a manner which tends to move the actual center of mass relative to the axis of thrust or line of action of the thruster. In one embodiment of the invention, the controllable coupling arrangement includes a manifold for coupling propellant from the tanks to the thruster, a tank of pressurizing gas, and a controllable manifold coupling the tank of pressurizing gas to the propellant tanks.

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: A spacecraft control system having a spacecraft with a gimbaled thruster attached thereto. An actuator is operationally attached to the gimbaled thruster to control the angled position of the gimbaled thruster in two orthogonal directions. A position control system is provided which sends a control signal to the actuator which moves the gimbaled thruster to an angled position in response to the control signal, wherein the angled position of the gimbaled thruster controls the attitude and orbital velocity of the spacecraft.

Abstract: A satellite designed to be spin-stabilized in geostationary orbit which has, coaxial with a spin rotation axis, a satellite body surrounded with a cylindrical solar generator, an apogee maneuver system disposed along the axis and two axially disposed equipments. The apogee maneuver system has opposite one of the equipments at least two thrusters oriented parallel to the axis but offset relative thereto by the same distance. Equi-angularly spaced around the other of the two equipments, the thrusters are connected to a common liquid propellant feed system.

Abstract: A spacecraft, such as a geosynchronous weather or communications satellite, is constructed to include a plurality of low thrust thrusters mounted at predetermined locations on at least one of a spacecraft appendage or a spacecraft bus. The plurality of low thrust thrusters are fired in pairs for at least one of removing a disturbance torque or providing fine pointing attitude control. In one embodiment the low thrust thrusters are mounted on a solar array panel, thereby increasing the moment arm and enhancing the thrust output of the low thrust thrusters. In one embodiment a spacecraft has a plurality of low thrust thrusters arranged as at least two sets of two low thrust thrusters, individual ones of the low thrust thrusters of a set being disposed in a V-configuration and mounted at predetermined locations on at least one of a spacecraft appendage or a spacecraft bus. The plurality of low thrust thrusters are selectively fired for achieving control of 3-axes of spacecraft attitude or momentum.

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: Control moment gyros in an array are rotated to reorient a satellite by an attitude signal. If the signal causes a gyro to have position that will produce a singularity in attitude control, a disturbance is introduced into the signal to avoid the singularity.

Abstract: Spacecraft stationkeeping and momentum-dumping methods are facilitated by the use of selected diagonal pairs of thrusters which are positioned adjacent to nadir or antinadir spacecraft faces. The methods maintain an elliptical Sun-synchronous orbit, counter triaxiality forces and facilitate momentum-dumping of momentum and/or reaction wheels. They are particularly suited for inclined orbits.

Abstract: A spacecraft includes a thruster coupled to an outward-facing portion of each solar array such that the thruster plume faces outward from the spacecraft. With the thruster located outboard of any erosion-sensitive surfaces on the spacecraft, the thruster exhaust is directed away from the spacecraft. Since canting of the thrusters is no longer required, the mounting of the thruster in the outward-facing portion of each solar array increases the effective Isp of the thruster. A thruster drive assembly is coupled to each solar array, adjacent to the thruster, for positioning the thruster such that any thruster exhaust is directed away from the spacecraft. A central supply tank is conveniently coupled to a central body portion of the spacecraft for providing a common propellant supply to each of the thrusters.

Abstract: Structures and methods are provided to effect satellite maneuvers in the presence of disturbance torques with enhanced fuel efficiency. A thruster control loop is combined with a wheel control loop in which the wheels respond to an estimate of the disturbance torques (e.g., an angular acceleration estimate, a thruster torque command or a filtered thruster torque command) to create a counteracting gyroscopic torque. Simulations of the invention's methods have shown they have the authority of all-thruster control systems and fuel efficiency that rivals that that of all-wheel control systems.

Abstract: A three-axis stabilized spacecraft having roll, pitch, and yaw axes and when on station in orbit about the earth having a north face and a south face is equipped with a first and second thruster which may be electric thrusters. A first support device mounts the first thruster adjacent the north face and the first thruster is positioned a spaced distance away from the north face in a first direction parallel to the pitch axis and spaced from the pitch axis in a second direction normal to the pitch axis. A second support device mounts the second thruster adjacent the south face, the second thruster being positioned a spaced distance away from the south face in a third direction opposite the first direction and spaced from the pitch axis in the second direction. A gimbal mechanism pivotally mounts the first and second thrusters on the first and second support devices, respectively, for selectively positioning the attitude of the first and second thrusters.

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: In a spacecraft that controls its position and attitude by a plurality of bipropellant thrusters, controlled ejection and vaporization of a single remaining propellant species generates a thrust force to adjust the spacecraft's position and attitude, thereby allowing an extension of the spacecraft's useful life after the other propellant has been exhausted.

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 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: Satellite stationkeeping and momentum-dumping methods are facilitated by the use of diagonally-arranged thruster pairs which are positioned on a selected one of a nadir and an antinadir satellite face. A first one of the thruster pairs is directed so that its thruster forces are spaced by moment arms from the satellite's center of mass. Firings of this thruster pair are separated by a momentum-dumping right ascension difference that is chosen to enhance momentum authority. These firings generate momentum-dumping torques and contribute to stationkeeping velocity changes. A second one of the thruster pairs is directed so that its thruster forces substantially pass through the center of mass. Firings of this thruster pair are separated by a stationkeeping right ascension difference chosen to minimize fuel consumption while providing a major portion of stationkeeping velocity changes.

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 method of simultaneously controlling East/West and North/South positioning and unloading momentum of a spacecraft while orbiting an object. The spacecraft has a thruster array and a momentum accumulator. The method entails moving said spacecraft towards a node of the orbit. At a predetermined position on the orbit, separate from the node, a thruster of the thruster array is fired so as to control the orbital position of the spacecraft. While the thruster is being fired, momentum is dumped from the momentum accumulator at the predetermined position so that any loss in control in the attitude of the spacecraft is reduced.

Abstract: A three-axis stabilized spacecraft is subject to a velocity change in a desired direction by a thruster. Unavoidable alignment errors cause a body torque, which tends to slew the body away from the attitude which orients the thrust axis in the direction. The attitude control system eventually corrects the attitude, but the thrust during the attitude transient results in an error in the direction of the velocity change. This error in the direction accumulates during the attitude transient. When the attitude transient passes, no further pointing error occurs. A control system, operating without an accelerometer, determines the total error accumulated during the attitude transient, and processes the error signal to generate a supplemental torque demand signal, which is added to the torque demand signal produced by the attitude control system, to cause an oppositely-directed attitude transient to thereby cancel the original velocity change direction error.

Abstract: A spacecraft includes a plurality of thrusters mounted at predetermined locations on a spacecraft structure, individual ones the plurality of thrusters being fired for generating a torque about a desired axis. The firing of a thruster is partitioned into two firings that are offset in time by an amount .DELTA.t, wherein .DELTA.t=(1/2).times.(1/F).times.SF, where F is a dominant modal frequency, in Hertz, for any particular axis (nominally the 1st mode) of the spacecraft structure, and where SF is a scale factor that is adjustable about the frequency. In a presently preferred embodiment the thruster is a low thrust thruster that is mounted on a solar array panel, and the thrusters are fired in pairs.

Abstract: A filter for use in an attitude control system which may be subjected to vibrations from disturbances which have frequency contents that vary with time. Sensors on the system produce signals that contain the disturbance frequencies and a calculator connected to the source of disturbance produces a signal which varies as a function of the disturbance. The filter receives these signals and augments the control loop gain at the disturbance frequencies thereby enabling the attitude control devices to null the disturbance effects on the attitude of the system.

Abstract: In a process and apparatus for controlling the attitude of a spacecraft, drive signals for driving attitude control units of the spacecraft are generated based on control unit signals related to the three principle axes of a spacecraft oriented coordinate system, using the rule k=B.sup.I e+cu.sub.2. The drive matrix B.sup.I, a definite vector u.sub.2 and the constant c result from the application of a matrix decomposition according to the Singular Value Decomposition (SVD) method to a nozzle matrix B. The latter matrix contains as elements, the momentum and force vectors which can be generated by the attitude control units, and the drive matrix B.sup.I is multiplied directly with the vector e derived from the axis-related control unit signals.

Abstract: A spacecraft traveling in a volume of space receiving radiation from a radiation source and having a spacecraft body having a first axis of symmetry, X, a second axis of symmetry, Y, and a third axis of symmetry, Z. The spacecraft body rotates about a rotation axis, T, which defines a nonzero angle of inclination .lambda. relative to the Z axis. A radiation receiving element is rotatably attached to the spacecraft body along an axis, S. A control system is employed on the spacecraft for rotating the spacecraft body about the rotation axis T by an angular amount .gamma. and rotating the radiation receiving element by an amount so that the radiation receiving element is normal to the radiation source.

Abstract: Satellites are launched to a first orbit on a launch rocket. The satellites are connected together, forming a satellite cluster, that is propelled from the first orbit to a higher mission orbit by thrustors on each satellite. The satellite cluster is formed so that satellite cluster rotation from aerodynamic drag on the individual satellites is minimized. The thrustors are sequenced to control satellite cluster attitude during the transition to the second altitude. At the second altitude, the satellites are separated from the satellite cluster and propelled to their mission orbits using their own thrustors and attitude system.

Abstract: There is disclosed an angle positioning platform for positioning objects around first and second axes and a gearbox for same. The platform comprises a base, an intermediate stage, and an upper stage. The platform may have motors and first and second output gearboxes connected to the motors for driving the platform. The orientation of the stages of the platform permits the platform to be relatively compact in a stowed position and to have high angular rotation from the stowed position to a maximum travel position. The gearboxes may have a mechanism for isolating worm shafts and wormgears from heavy loads when the platform is in the stowed position. Another aspect of the invention is an output gearbox with a wormgear having stops for stopping rotation of a matingly engaged worm. Another aspect of the invention is a gearbox having torsion springs to counter backlash in the gearbox.

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: In the present invention four thrusters are provided as a group of thrusters for collision avoidance. These thrusters contain a component of translational thrust for collision avoidance injection in their respective outputs, and are capable of simultaneously generating posture control torque around two coordinate axes, which are orthogonal to a thrust axis, in order to maintain the directional stability of the thrust axis during the injection. When abnormality arises in a group of thrusters for ordinary use, collision avoidance is executed by replacing all the thrusters for ordinary use by these thrusters for collision avoidance.

Abstract: A spacecraft includes a body defining a center of mass, and an attitude control system, for generating attitude error signals representing deviation of the body from a desired attitude. A plurality of thrusters mounted on the body have nominally parallel thrust components, in a particular direction. The thrusters are arranged in pairs, which produce opposed torques. A velocity change controller is coupled to the thrusters, for generating pulsatory firing command signals for the thrusters for a particular total time duration, for achieving a desired velocity change in the desired direction.

Abstract: In a Hall effect thruster, especially for use in maneuvering satellites, a stream or plume of ions, used to produce the thrust is deflected, by appropriate adjustment of a magnetic field, so as to steer the satellite or other vehicle. The channel, along which the ions are accelerated, is preferably flared outwardly at its open end so as to avoid erosion which would otherwise be caused by the deflection. The adjustment of the magnetic field is preferably achieved by dividing an outer magnetic pole, surrounding the channel, into separate sectors and winding individual electric coils around the sectors. Control of the current through these individual coils is used to make the appropriate adjustments of magnetic field.