Lee W Barker

US Patent:

6453220, Sep 17, 2002

Filed:

Jan 31, 2000

Appl. No.:

09/493595

Inventors:

Lee A. Barker - San Jose CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

G05D 100

US Classification:

701 3, 701 14-, 701 13, 701226, 701300

Abstract:

An easily implementable satellite constellation stationkeeping algorithm for maintaining the relative positioning among satellites of a low earth orbit constellation with minimal maneuvering while maintaining the constellation altitude over the effects of atmospheric drag. The satellite constellation stationkeeping algorithm may be implemented as a system or method that uses atmospheric drag perturbations to extend the stationkeeping cycle of the satellites in the low earth orbit constellation while simplifying the implementation algorithm and performing minimal maneuvers. In an exemplary satellite constellation stationkeeping algorithm, a plurality of satellites or a ground station are configured with a controller that implements an absolute altitude control algorithm. The plurality of satellites are launched into a respective plurality of slots of a low earth orbit. The orbital position of each satellite is controlled using the absolute altitude control algorithm such that each satellite is allowed to drift to or near the edge of a positional box that defines its slot, and the altitude of each satellite is selectively driven to a fixed target altitude which is a function of position and drag, using one or more thrusters for example, to reverse the satellite drift in its slot.

US Patent:

20040046691, Mar 11, 2004

Filed:

Aug 22, 2002

Appl. No.:

10/225972

Inventors:

Lee Barker - San Jose CA, US
Xenophon Price - Redwood City CA, US

International Classification:

H04B007/185

US Classification:

342/355000, 342/358000

Abstract:

Payload performance is optimized by determining yaw trajectory employing a method which develops a mathematical expression to define the payload in terms of ‘n’ location(s) on the earth; determining the pointing error of the ‘n’ location(s); combining the error so as to product a single performance parameter and minimizing the value of the performance parameter by appropriately varying yaw.

US Patent:

62531255, Jun 26, 2001

Filed:

Mar 1, 2000

Appl. No.:

9/516927

Inventors:

Lee A. Barker - San Jose CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 124

US Classification:

701 13

Abstract:

Satellite control data in the form of state vectors and state vector products are generated representing the position and geometric relationships of the space craft to the Earth, sun, moon, and specific locations on the Earth. These data is used to control attitude, SADA steering, antenna pointing, momentum upload, and Earth sensor intrusion. An onboard orbit propagator predicts the data and integrates the data into the various control systems for the respective function.

US Patent:

61645974, Dec 26, 2000

Filed:

Aug 5, 1999

Appl. No.:

9/368980

Inventors:

Lee A. Barker - San Jose CA
Benjamin Lange - San Francisco CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 124

US Classification:

244168

Abstract:

Methods that provide stationkeeping maneuvering of a yaw steered spacecraft that orbits around a central body, such as the Earth, and experiences solar radiation pressure produced by the sun. The methods comprise the following steps. A spacecraft having a solar array is launched into orbit at a desired orbital location. Once the spacecraft is in orbit at the desired orbital location, a reflected component of the solar radiation pressure is caused to selectively apply a force to the spacecraft that moves the spacecraft to perform stationkeeping maneuvers. The reflected component of the solar radiation pressure may be caused to selectively apply a force to the spacecraft in two exemplary ways. In one embodiment, the spacecraft is yaw steered to follow a yaw steering profile so that the axis of the solar array is substantially normal to a plane containing the sun vector and nadir vector. The orbit of the spacecraft is then controlled to provide stationkeeping by applying an additional bias to the yaw steering profile.

US Patent:

62378767, May 29, 2001

Filed:

Jul 28, 2000

Appl. No.:

9/627482

Inventors:

Lee A. Barker - San Jose CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

B64G 124

US Classification:

244164

Abstract:

Satellite attitude control methods for use during orbit raising operations to follow a predefined thrust trajectory that meets geometric constraints imposed by sensor and/or telemetry and control antenna fields of view while optimizing the sun angle on the solar array. The method uses low thrust electric propulsion for geosynchronous satellite orbit raising from a transfer orbit to the final geosynchronous orbit. In implementing the methods, a predefined thrust trajectory is generated that is designed to raise a satellite from a transfer orbit to a geosynchronous orbit. A direction-cosines matrix, or quaternion, is generated that aligns a thrust vector defined in the satellite body frame with the predefined thrust trajectory and rotates the satellite body about that vector. Attitude control is performed in accordance with the direction-cosines matrix to align the thrust vector defined in the satellite body frame with the predefined thrust trajectory and rotate the satellite body about that vector to optimize the sun angle on the solar array.

US Patent:

63176602, Nov 13, 2001

Filed:

May 25, 2000

Appl. No.:

9/578992

Inventors:

Lee A. Barker - San Jose CA
Xenophon Price - Redwood City CA

Assignee:

Space Systems/Loral, Inc. - Palo Alto CA

International Classification:

G05D 100
G05D 300
G06F 700
G06F 1700
G06F 1900

US Classification:

701 13

Abstract:

A method for use on a satellite that automatically inhibits scanning of an Earth sensor to handle sensor intrusions by the sun, moon, or other celestial bodies. In implementing the method, a predicted state vector for the satellite, derived from an orbit propagator, is generated. An attitude profile for the satellite is generated. Then, the satellite state (predicted state vector) and attitude profile are processed to determine Earth, sun, and moon vectors in a satellite body frame of reference at any instant. The Earth, sun, and moon vectors are compared to the Earth sensor field of view and sensor field of view limit boxes to determine if scan inhibiting or Earth sensor switching should occur. The affected Earth sensor is inhibited or switched if an intrusion of the sun and/or moon into the field of view of the Earth sensor is predicted.