Kam W Chan

US Patent:

57873682, Jul 28, 1998

Filed:

Nov 3, 1995

Appl. No.:

8/552613

Inventors:

Donald W. Gamble - Menlo Park CA
Xenophon H. Price - Menlo Park CA
Kam Kin Chan - San Jose CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 124

US Classification:

701 13

Abstract:

An attitude or orientation control system for spacecraft that provides for yaw axis error reduction and momentum dumping using a simple calculation involving only the momentum wheel speeds as input and which outputs two axis (roll and yaw) torque commands. The system utilizes the spacecraft 1) momentum wheels that store spacecraft momentum, 2) processing means for the calculation of control torques, and 3) torque actuators, e. g. , magnetic torquers, that can provide a torque axis anywhere in the spacecraft roll/yaw plane, and involves three fundamental steps, 1) the input of the momentum wheel speed mearsurements, and 2) the calculation of the required torques, using the wheel speed measurements, and and 3) the outputting of the required torques in a form appropriate for controlling the available actuators.

US Patent:

61424226, Nov 7, 2000

Filed:

Jun 21, 1999

Appl. No.:

9/337078

Inventors:

Jeffery D Stoen - Palo Alto CA
Kam Chan - San Jose CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 126

US Classification:

244164

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.

US Patent:

60682175, May 30, 2000

Filed:

Sep 22, 1997

Appl. No.:

8/934981

Inventors:

Jeffery D Stoen - Palo Alto CA
Kam Chan - San Jose CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 126

US Classification:

244164

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.

US Patent:

59574119, Sep 28, 1999

Filed:

Dec 24, 1997

Appl. No.:

8/998173

Inventors:

Tung Y Liu - Union City CA
Kam K Chan - San Jose CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 126

US Classification:

244169

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.

US Patent:

60534559, Apr 25, 2000

Filed:

Jan 22, 1998

Appl. No.:

9/010718

Inventors:

Xen Price - Redwood City CA
Thomas Randolph - San Carlos CA
Kam K. Chan - San Jose CA
Ahmed Kamel - Los Altos CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 126

US Classification:

244169

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.