Abstract: A system and method for controlling de-orbit of a spacecraft is presented. Embedded command modules are commanded directly from a central command and telemetry module. Latch valves, thruster valves, and solar wing drive of the spacecraft are operated in response to inputs to the embedded command modules. The spacecraft is maneuvered to a safe disposal orbit in response to commands from the central command and telemetry unit.

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 spacecraft with a reaction wheel system can be autonomously safed by setting the solar wings to continuous tracking, determining a slew rate vector based on the total angular momentum, and slewing the spacecraft using the slew rate vector until commanded to stop autonomous safing. In a typical application, the spacecraft has a reaction wheel assembly with four wheels arranged to form a right regular pyramid. Two reaction wheels on opposite edges of the pyramid form a first pair and the two remaining reaction wheels forming a second pair. The slew axis of rotation is found by determining as a selected pair the first pair if either reaction wheel in the second pair is inoperative, otherwise determining as the selected pair the second pair and determining as the slew axis of rotation the normalized projection of the axes of rotation of the selected pair onto the base. The slew direction is determined by the sign of the total angular momentum component along the slew axis of rotation.

Abstract: A system and method for acquiring the Earth by a three-axis stabilized spacecraft in the presence of a significantly time-varying Sun-Earth angle including obtaining an Earth cone described by rotating the nadir vector about the Sun vector, slewing the spacecraft about an axis until the Earth sensor boresight touches an edge of the Earth cone, updating the Earth cone due to the changing Sun-Earth separation angle, performing a spiral coning maneuver about the updated Earth cone until the Earth sensor detects the Earth, and locking onto the Earth so as to hold the Earth sensor boresight coincident with the nadir vector. Additionally, the spacecraft may be rotated about the nadir vector so as to bring the spacecraft into a desired final attitude.

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 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.