Use of nonlinear identification in robust attitude and attitude rate estimation for SAMPEX
Abstract
A method is described for obtaining optimal attitude estimation/identification algorithms for spacecraft lacking attitude rate measurement devices (rate gyros), and then demonstrated using actual flight data from the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) spacecraft. SAMPEX does not have onboard rate sensing, and relies on sun sensors and a threeaxis magnetometer for attitude determination. The absence of rate data normally reduces both the total amount of data available and the sampling density (in time) by a substantial fraction. In addition, attitude data is occasionally unavailable (for example, during sun occultation). As a result, the sensitivity of the estimates to model uncertainty and to measurement noise increases. In order to maintain accuracy in the attitude estimates, there is an increased need for accurate models of the rotational dynamics. The Minimum Model Error(MME)/Least Square Correlation(LSC) algorithm accurately identifies an improved model for SAMPEX to be used during periods of complete data loss or extreme noise. The model correction is determined by estimating only one orbit(the identification pass) just prior to the assumed data loss(the prediction pass). The MME estimator correctly predicted the states during the identification phase, but more importantly determines the necessary model correction trajectory, d(t). The LSC algorithm is then used to find this trajectory's functional form, H(x(t)). The results show significant improvement of the new corrected model's attitude estimates as compared to the original uncorrected model's estimates. The possible functional form of the correction term is limited at this point in the study to functions strictly of the estimated states. The results, however, strongly suggest that functions based on the relative position of the satellite may also be possible candidates for future consideration.
 Publication:

Flight Mechanics/Estimation Theory Symposium 1995
 Pub Date:
 May 1995
 Bibcode:
 1995fmet.symp..217M
 Keywords:

 Algorithms;
 Attitude (Inclination);
 Explorer Satellites;
 Least Squares Method;
 Mathematical Models;
 Nonlinearity;
 Optimal Control;
 Parameter Identification;
 Satellite Tracking;
 State Estimation;
 Statistical Analysis;
 Correlation;
 Errors;
 Gyroscopes;
 Magnetometers;
 Solar Sensors;
 Spacecraft Trajectories;
 Spectral Sensitivity;
 Three Axis Stabilization;
 Astrodynamics