Hughes Electronics Corporation

The Boeing Company

Hughes Aircraft Company

Other

Bernard M Anzel

Yiu-Hung Monte Ho

Richard A Noyola

John F Yocum, Jr

David K Abernethy

Keith F Keitel

A method for performing east-west station keeping for a satellite in an inclined synchronous orbit is described. The method includes averaging a value of a right ascension of the ascending node for an inclination vector associated with the satellite over a period of the control cycle, and managing corrections for the satellite such that an eccentricity vector, directed at perigee, is substantially collinear with the inclination vector.

Methods and apparatus for node-synchronous eccentricity control

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. The normal tangential and radial thrust components of the thruster systems are arranged so that station changing, station keeping and momentum dumping are still realized after the failure of any thruster pair.

Thruster systems for spacecraft station changing, station keeping and momentum dumping

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.

Stationkeeping and momentum-dumping thruster systems and methods

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.

Fuel efficient methods for satellite stationkeeping and momentum dumping

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.

Momentum unloading using gimbaled thrusters

A geostationary orbital box is divided by radially-oriented planes to form orbital sub-boxes. A thruster system facilitates station keeping satellites in each of these orbital sub-boxes. The thruster system includes thruster pairs that are positioned on an anti-nadir face of each satellite and directed through the satellite's center of mass. In addition, multiple satellites can be stationed in each of the sub-boxes by causing them to rotate in a chosen one of a clockwise and a counterclockwise direction and to be spaced from each other in at least one of a radial direction and a normal direction. To enhance the fine-grain control of each of the satellites, the thruster system preferably uses ion-propulsion thrusters.

Satellite co-location methods

A method of stationkeeping for a three-axis stabilized satellite having four thrusters mounted in a generally rectangular configuration on an anti-nadir face of the satellite, each of the four thrusters having a line of thrust which passes through the center of mass of the satellite, the four thrusters including a northwest thruster, a northeast thruster, a southwest thruster, and a southeast thruster. The method includes the step of rotating the satellite about a pitch axis that is perpendicular to a normal to the anti-nadir face of the satellite. The northwest thruster and the northeast thruster are canted away from the anti-nadir face in a north direction with respect to a north-south axis which passes through the center of mass of the satellite. The southwest thruster and the southeast thruster are canted away from the anti-nadir face in a south direction with respect to the north-south axis. The northeast thruster and the southeast thruster are slewed in an east direction about the north-south axis and the northwest thruster and the southwest thruster are slewed in an west direction about the north-south axis. Next, the northeast thruster and the northwest thruster are fired near an orbit ascending node and the southeast thruster and the southwest thruster are fired near an orbit descending node, wherein each of the four thrusters is fired in accordance with the amount that the satellite is rotated about the pitch axis.

Method and apparatus for stationkeeping a satellite offset by pitch

A method and apparatus for satellite station keeping is disclosed in which six thrusters are mounted on the anti-nadir face of a satellite with their direction of thrust passing through the center of mass (CM) of the satellite. The thrust lines of the north trio of thrusters and the south trio of thrusters make an angle .theta. with the satellite north-south axis in a northern and southern direction, respectively. The four outer thrusters are laterally separated and slewed by an angle .alpha. about the north-south axis. Each outer thruster produces three components of .DELTA.V, i.e. normal, tangential and radial (toward the Earth), thereby providing complete control of the three orbit vectors, inclination, eccentricity and mean motion. The north and south center thrusters are positioned in the Local-Vertical North-South plane and produce only normal and radial .DELTA.V components, providing control for momentum dumping and, in the event of failure, inclination control. In the event of a thruster failure where one of the pairs of thrusters is shut down, four thrusters remain to maintain station keeping.

Method and apparatus for a satellite station keeping

A method and apparatus for satellite station keeping is disclosed in which four thrusters are mounted on the anti-nadir face of the satellite with their direction of thrust passing through the center of mass of the satellite. The thrust lines of the north pair (20, 22) of thrusters and the south (24, 26) pair of thrusters make an angle .theta. with the satellite north-south axis in a northern and southern direction respectively. The thrusters are laterally separated and slewed by an angle .alpha. about the north-south axis. Each thruster produces three components of .DELTA.V, i.e. normal, tangential and radial (toward the Earth), thereby providing complete control of the three orbit vectors, inclination, eccentricity and mean motion. In the event of failure of a thruster, the thruster diagonally opposite the failed thruster is shutdown and the remaining diagonal pair of thrusters is used to maintain station keeping.

An improved method for satellite station keeping is disclosed. The method provides for station keeping of a three axis stabilized satellite 10 using only two thrusters 20 and 22. The thrusters 20 and 22 can be ion or liquid propulsion thrusters and are mounted on the anti-nadir face 18 of the satellite 10. The north thruster 20 is canted at an angle .THETA. from the north-south axis 16 of the satellite 10 in a northern direction and the south thruster 22 is canted at the angle .THETA. from the north-south axis 16 in a southern direction. Both thrusters 20 and 22 are also translated to the east or west along an east-west axis 14 of the satellite 10 and swiveled at variable angles .alpha..sub.1 and .alpha..sub.2 respectively. A specific teaching of the invention discloses techniques for determining the angles .alpha..sub.1 and .alpha..sub.2 and the firing positions for the thrusters 20 and 22 to maintain the satellite 10 in a stationary orbit. In a specific embodiment, a backup thruster 24 is provided to counter the radial acceleration buildup from a failure of one of the thrusters 20 or 22. Also, in a specific embodiment, first and second slide mechanisms are provided to translate the first and second thrusters 20 and 22 to the east or west along the east-west axis 14 of the satellite 10 for a change in the angles .alpha..sub.1 or .alpha..sub.2 in order to maintain the lines of thrust from the thrust of the thrusters 20 and 22 respectively through the center-of-gravity of the satellite 10.

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El Segundo, CA, United States of America

Bernard M Anzel