Attitude Determination of Satellites by Means of Real Time Data Processing

Abstract

The attitude of a satellite is very important not only for scientific observations but also for the house keeping, and attitude control of satellites is desirable. In order to accomplish the attitude control, measurements and determination of the attitude are necessary.
In this paper, the attitude determination of satellites by means of real time data processing is discussed.
Random errors are generally introduced to the output data of the sensors due to the noise in the electronic circuits and the random variation of the physical quantities measured, such as time and spatial variations of horizon. In the determination of the attitude, the choice of data processing in addition to the improvement of the acuracy of each sensor is necessary.
In this paper, attitude control using the geomagnetic field is assumed, and a filtering technique is applied to the attitude determination, which offers the basis of planning the attitude control. A method of attitude determination using a horizon sensor and a digital sun sensor is discussed, and the equations for the attitude determination are developed. The errors which should be expected in the measurements by each sensor are also discussed. By use of these results, digital simulations are made, and the accuracy and the time required in the attitude determination are studied. A sequential least squares method neglecting the dynamics of the attitude from the filtering technique is also discussed by simulations. The examples of the simulation show that 1∼4 degrees divergence in the attitude angle obtained from raw data can be improved to 0.1∼1 degree by both methods. When the filtering is applied and the estimated values of parameters in dynamics deviate largely from the true values, the error increases very greatly. From these facts, it is expected that the sequential least squares method is applicable in practice. It is confirmed that the attitude can be determined by both methods in one orbital period by utilizing all the data on the attitude in the orbit.