A Method For Controlling The Attitude Of A Satellite Using The Earth S Magnetic Field

NASA Technical Note

A Method for Controlling the Attitude of a Satellite Using the Earth's Magnetic Field

The report investigates a means of controlling the attitude of a satellite in a circular orbit about the earth by the torque due to the interaction between the earth's magnetic field and the magnetic moments produced by currents in three orthogonal coils aboard the satellite. This system has the advantage over more conventional ones in that no mass is expended in the control process. It is designed to rotate the satellite about its longitudinal axis in a minimum amount of time while limiting the deviation of this axis from the local normal to the earth. The analysis is limited to the period during which the satellite's attitude is being changed by magnetically produced torques. When these torques are not applied, gravity gradient effects act as a restoring force to align the longitudinal axis with the local normal to the earth. The method is applicable to a satellite with symmetry such that the moment of inertia about its longitudinal axis is much smaller than those about body-fixed axes lying in a plane perpendicular to it and whose moments of inertia about axes in this plane are approximately equal. The model of the earth's magnetic field that is used is a dipole with its poles located at the observed geographical positions. The control system is developed to be applicable to the general type of satellite indicated above and to all orbits except those passing close to the magnetic poles. It is then applied to a particular satellite and type of orbit of interest to RADC. (Author).

Spacecraft Attitude Determination and Control

Roger D. Werking Head, Attitude Determination and Control Section National Aeronautics and Space Administration/ Goddard Space Flight Center Extensiye work has been done for many years in the areas of attitude determination, attitude prediction, and attitude control. During this time, it has been difficult to obtain reference material that provided a comprehensive overview of attitude support activities. This lack of reference material has made it difficult for those not intimately involved in attitude functions to become acquainted with the ideas and activities which are essential to understanding the various aspects of spacecraft attitude support. As a result, I felt the need for a document which could be used by a variety of persons to obtain an understanding of the work which has been done in support of spacecraft attitude objectives. It is believed that this book, prepared by the Computer Sciences Corporation under the able direction of Dr. James Wertz, provides this type of reference. This book can serve as a reference for individuals involved in mission planning, attitude determination, and attitude dynamics; an introductory textbook for stu dents and professionals starting in this field; an information source for experimen ters or others involved in spacecraft-related work who need information on spacecraft orientation and how it is determined, but who have neither the time nor the resources to pursue the varied literature on this subject; and a tool for encouraging those who could expand this discipline to do so, because much remains to be done to satisfy future needs.