1. Field of the Invention
The present invention relates to a system for an intelligent attitude and orbit control of a satellite, and more particularly to improved intelligent control apparatus and method where autonomous attitude and orbit control are performed onboard a satellite in normal and contingency modes.
2. Description of the Conventional Art
Conventionally, attitude determination and control are performed automatically onboard a satellite. There are patents to improved the accuracy of the attitude control system using inertial sensor and the star sensor. See U.S. Pat. No. 4,617,634, entitled, "Artificial Satellite Attitude Control System," dated Oct. 14, 1986. On the other hand, conventional orbit control method requires tracking of the satellite from the ground, calculation of the parameters to change the orbit, and transmitting commands to the satellite. But this method requires much financial and human resources. Also there exists potential for the human error in the process. Thus, Wertz proposed the method of maintaining an assigned orbit without control or intervention from the ground. See U.S. Pat. No. 5,528,502, entitled "Satellite Orbit Maintenance System," dated Jan. 18, 1996. The present invention provides a method and apparatus to control both attitude and orbit of a satellite autonomously based on intelligent decisions onboard the satellite.
For controlling orbit and attitude of a satellite automatically, the position of a satellite has to be determined (Navigation technique), and controlled (Guidance technique).
Navigation and guidance technique is being actively studied and some of them are being registered as patents.
Navigation technique is reported in the paper, "Autonomous Navigation" C. Jayles, F. Alby, J. Berthios, D. Pradines, Spaceflight Dynamics Part II, Edited by Jean-Pierre Carrou, CNES, 1995. And Navigation technique is disclosed as a patent, "Method and Apparatus for predicting the position of a satellite in a satellite based navigation systems (U.S. application Ser. No. 5,430,657).
Also, Guidance technique is reported in "TOPEX/POSEIDON Autonomous Maneuver Experiment (TAME) Design and Implementation" by T. Kia, J. Mellstrom, A. Klumpp, T. Munson, and P Vaze, Advances in the Astronautical Sciences, Guidance and Control 1997, Edited by Robert Culp and Stuart Wiens, American Astronautical Socienty Publication, pp. 41-56.
There are several reports and registered patents, for attitude control e.g., U.S. Pat. Nos. 5,534,965, 5,458,300 and 5,412,574.
It is desirable to have a system where the attitude the the orbit are maintained autonomously onboard the satellite autonomously onboard the satellite during the normal operational mode. Furthermore, in the contingency situation such as when the collision danger exists or when a sensor or an actuator fails, we require the satellite to maneuver automatically to avoid the collision or to operate without the failed sensor. Thus, an intelligent decision making process for the attitude and orbit control are highly desired quality.