Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reexamination Certificate
2000-02-24
2001-09-18
Zanelli, Michael J. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C244S166000
Reexamination Certificate
active
06292722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to control of orbiting spacecraft, especially for controlling spacecraft yaw and roll excursions caused by solar torques and thruster firings and, more particularly, for augmenting magnetic torquer management of solar torque with thruster availability in case larger than expected external torques are imparted on the spacecraft.
2. Description of the Prior Art
Earth-orbiting spacecraft, such as communications satellites, require orientation control to minimize excessive movements in pitch, yaw, and roll, that can effect their remaining in proper orbit, and that can interfere with their pointing in a proper direction to insure the reception of signals transmitted therefrom at receiving stations on the ground. Various systems are provided on the spacecraft to affect this control involving momentum wheels, thrusters, magnetic torquers, and sensors for yaw, roll, and pitch. For example, one such control system uses momentum bias for preventing the set yaw orientation from drifting. However, the spacecraft is regularly undergoing disturbances, from such factors as solar torques and thruster firings, that can cause variations in the yaw angle from the desired orientation and beyond allowable ranges of operation. The current approach to dealing with this problem uses a combination of the yaw sensors and magnetic torquers to maintain the desired yaw orientation.
Unfortunately, there are variations in the earth's magnetic field and, indeed, it even disappears on occasion rendering the magnetic torquers less effective or even totally ineffective. Furthermore, there are often disturbances on the spacecraft itself which affect the capability of the magnetic torquers. For example, magnetic torquers are known to interact adversely with solar torques and with the B-Field, that is, the earth's magnetic field. Still another drawback of known systems is that when a maneuver is performed by the spacecraft, torque disturbances are thereby imparted to the spacecraft which are often sensed by the computer as a solar torque or a B-field anomaly. To avoid excessive correctional operations by the magnetic torquers under the direction of the on-board computer, it is therefore often necessary to temporarily disable the magnetic torquers, sometimes for an extended duration.
It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice. The actuation and deployment concept embodied by this invention is different from all of the devices reviewed above.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus and method for controlling yaw and roll excursions in a spacecraft having on-board components such as magnetic torquers, a roll thruster, momentum wheels, a wheel controller, an earth sensor, and a Digital Integrating Rate Assembly (DIRA). An observer module on the spacecraft receives inputs containing information comprising the unbiased roll error from the earth sensor, yaw momentum measured from the wheel speeds, and commanded yaw and pitch momentum output from the wheel controller, and produces therefrom output signals indicative of yaw estimate, yaw momentum estimate and torque disturbances estimate. A controller module on the spacecraft receives the output signals and combines them with inputs containing information comprising minimum yaw error and roll thrust yaw controller gain and minimum yaw error and roll thrust yaw momentum controller gain, and produces therefrom a signal for commanding the operation of the magnetic torquers to change roll momentum when within the dead band of the signal and, alternatively, for commanding the operation of both the magnetic torquers and the roll thruster to change roll momentum when the threshold of the dead band is exceeded. By so doing, the yaw attitude and yaw excursions are controlled.
A primary feature, then, of the present invention is the provision of a spacecraft control system in which magnetic torquers and thrusters are in active control simultaneously.
Advantages of the system of the invention over known prior art include the following:
(1) it manages momentum with larger than expected momentum disturbances;
(2) it manages momentum with magnetic torquer failure;
(3) it manages momentum through magnetic storms;
(4) it can operate through thruster unloads;
(5) it can operate through EW stationkeeping maneuvers;
(6) it can operate through NS stationkeeping maneuvers;
(7) it can operate through fuel slosh momentum shifts;
(8) it can operate through initial on-orbit out-gassing events;
(9) it only fires thrusters in extenuating circumstances;
(10) it fires thrusters without operator intervention; and
(11) it manages wheel speed run off with magnetic torquers.
Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.
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Cielaszyk David
Holmes Thomas J.
Gibson Eric M
Perman & Green LLP
Space Systems Loral, Inc.
Zanelli Michael J.
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