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: An onboard attitude control system is constructed to utilize a four reaction wheel system having a reference axis, wherein at least three of the reaction wheel spin axes are oriented obliquely to the reference axis. Current attitude is estimated based on uploaded orbital data, onboard sensed earth and sun position data, and attitude data sensed by a three axes gyroscope system. Current attitude is compared to mission attitude to calculate an error which is transformed to a trihedral axes adjustment command to actuate the reaction wheel system.

Abstract: In an electric propulsion system used for transferring a satellite to its operational orbit, a solar array adjustment system is controlled to compensate on a continuous basis for the attitude gyrations required by electric thrust vector optimization. The solar array control operates to maintain the solar array in a perpendicular orientation to the sun vector for optimum power generation.

Abstract: A spacecraft orientation procedure, in accordance with a first embodiment of the invention, is practiced with a sun sensor to bring the x (roll) axis of the spacecraft parallel to a ray of the sun, and with a gyro sensor and an earth sensor of the spacecraft in conjunction with one instruction provided either autonomously or by a ground tracking station regarding an orientation of a spacecraft reference plane to enable locating the earth by the earth sensor. Furthermore, in accordance with a second embodiment of the invention, the orientation is established without aid from the ground tracking station by use of at least one telemetry and command antenna having a continuous field of view, as measured in one plane, which is greater than a semicircle. In the second embodiment, the orientation procedure provides for rotation of the spacecraft about the x axis for a scanning of the antenna to intercept command signals broadcast from the earth, thereby to locate the earth in a first reference plane.

Abstract: A spacecraft (201) maintains its north-south positioning by using one of two pairs of single-gimballed throttled thrusters (221-224) on a face of the spacecraft (201). The throttles (118) and gimbals (116) of the thrusters (221-224) are controlled to produce torques on the spacecraft (201) that will maintain a desired attitude for the spacecraft (201) while simultaneously desaturating the momentum stabilizing wheels ( 120, 121 ) of the spacecraft (201).

Abstract: An improved method for transitioning a spacecraft from a thruster (5) controlled, station keeping mode to an operational, on-orbit mode, in which attitude control is maintained using internal momentum wheels (3). The method first utilizes a thruster compensation technique to supplement the conventional transition mode control system. This compensation uses empirical thruster data to derate thruster (5) efficiency for extremely short pulse durations necessarily used in transition mode operation. Secondly, a three step deadbeat thruster (5) sequence is employed in which a first pulse linearizes spacecraft (1) motion prior to orienting and stopping nutation. This linearization provides improved accuracy in computing and shortens the waiting time for subsequent thruster (5) firings.

Abstract: The present invention is a control system for a seven-degree-of-freedom robotic arm. The robotic arm (10) includes two links (12 and 14), each having two degrees of freedom, and a spherical wrist (26) having three degrees of freedom. The kinematics of the spherical wrist are decoupled from the kinematics of the arm. The four degrees of freedom of the arm create a redundancy which provides versatility in the positioning of the arm. Fixing the redundant arm parameter and locating the end point (24) of the end effectuator path away from areas of limited mobility results in a marked simplification of the algorithms which describe the equations of motion of the arm. Additionally, further computation reduction can be achieved by updating the control gains less frequently than every microprocessor cycle, such as updating once for every five degrees of pitch angle rotation of either joint.