Kam H Chan

US Patent:

7277384, Oct 2, 2007

Filed:

Apr 6, 2000

Appl. No.:

09/544196

Inventors:

Kam Chan - San Jose CA, US
Mathew Lodge - San Jose CA, US
Shoou Jiah Yiu - Los Altos CA, US

Assignee:

Cisco Technology, Inc. - San Jose CA

International Classification:

G01R 31/08

US Classification:

370230, 370235, 709225

Abstract:

A program and a method for a gateway are provided to deny incoming calls to prevent overload. The program provides a maximum CPU utilization threshold CPUT, which is set by the user. When a new incoming call is presented to the packet telephony gateway, the program checks a present CPU utilization CPUP. If the present CPU utilization CPUP is greater than the threshold, the call is refused. This insures that sound quality of the calls currently being handled is maintained, and that existing calls are never dropped.

US Patent:

7874519, Jan 25, 2011

Filed:

Feb 22, 2007

Appl. No.:

11/709614

Inventors:

Bruce Brumfield - Vacaville CA, US
Xenophon H. Price - Redwood City CA, US
George E. White - San Jose CA, US
Philip C. Hirschberg - Fremont CA, US
Kam Chan - Saratoga CA, US

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 1/36

US Classification:

244171

Abstract:

Methods and apparatus for a spacecraft () orbiting about a celestial body such as the Earth to reacquire operational three-axis orientation with respect to that body. A method embodiment of the invention comprises determining () a set of actual conditions of the spacecraft, comprising a position of the spacecraft () in inertial space as a function of time and a set of angular rotation rates of the spacecraft () with respect to a coordinate frame of the spacecraft (), determining () an actual instantaneous direction of the sun with respect to the coordinate frame, and propagating () an estimated actual sun direction with respect to the coordinate frame as a function of time; determining () a desired sun direction with respect to the coordinate frame as a function of time; rotating () the spacecraft () and adjusting angular rotation rates of the spacecraft () so that an actual angle between the spacecraft () coordinate frame and the sun as a function of time substantially coincides with the desired sun direction with respect to the coordinate frame as a function of time; and, rotating () the spacecraft () around an axis defined by a line between the sun and the spacecraft until () the celestial body is observed by a celestial body sensor of the spacecraft.

US Patent:

20120097797, Apr 26, 2012

Filed:

Dec 15, 2011

Appl. No.:

13/326654

Inventors:

Byoungsam Woo - San Jose CA, US
Mohammad Saghir Munir - Union City CA, US
Kam K. Chan - Saratoga CA, US

Assignee:

SPACE SYSTEMS/LORAL, INC. - Palo Alto CA

International Classification:

B64G 1/10
G05D 1/00
B64G 1/24

US Classification:

2441586, 701 3

Abstract:

Three-axis spacecraft momentum management is performed for a spacecraft traveling along a trajectory, by an actuator including at least one thruster disposed on a single positioning mechanism. As the spacecraft travels along the trajectory, a desired line of thrust undergoes a substantial rotation in inertial space. When the spacecraft is located at a first location on the trajectory, the single positioning mechanism orients the thruster so as to produce a first torque to manage stored momentum in at least one of a first and a second of the three inertial spacecraft axes. When the spacecraft is located at a second location on the trajectory, the single positioning mechanism orients the thruster so as to produce a second torque to manage stored momentum in at least a third of the three inertial spacecraft axes.

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:

60006617, Dec 14, 1999

Filed:

Sep 22, 1997

Appl. No.:

8/935044

Inventors:

Xen Price - Menio Park CA
Kam Chan - San Jose CA
Jeffery Stoen - Palo Alto CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 124
B64G 138
B64G 136

US Classification:

244164

Abstract:

A feedback motion compensation (FMC) component for use in a spacecraft having a payload. The FMC component includes a controller having sensor data inputs and an open loop dynamics model that is driven by actuator commands to produce a high accuracy attitude estimate suitable for payload motion compensation.

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.