93-156
The Attitude Accuracy Consequences Of On-Orbit Calibration Of The Extreme Untraviolet Explorer Attitude Sensors By The Flight Dynamics Facility At Goddard Space Flight Center*
J. Hashmall** W. Davis** and R. Human***
Abstract
The science mission of the Extreme Ultraviolet Explorer (EUVE)
requires attitude solutions with uncertainties of 27, 16.7, 16.7 arcseconds (3a) around the roll, pitch, and yaw axes, respectively. The primary input to the attitude determination process is provided by two NASA standard fixed-head star trackers (FHSTs) and a Teledyne dry rotor inertial reference unit (DRIRU) 11. The attitude determination requirements approach the limits attainable with the FHSTs and DRIRU. TheFlight Dynamics Facility (FDF) at GSFC designed and executed calibration procedures that far exceeded the extent and the data volume of any other FDF-supported mission. The techniques and results of this attempt 10 obtain attitude accuracies at the limit of sensor capability and the results of analysis of the factors that limit the attitude accuracy are the primary subject of this paper.
The success of the calibration effort is judged by the resulting measurement residuals and comparisons between ground- and onboard-determined attitudes. The FHST star position residuals have been reduced to less than 4 arcsec per axis‹a value that appears to be limited by the sensor capabilities. The FDF ground system uses a batch least-squares estimator to determine attitude. The EUVE onboard computer (OBC) uses an extended Kalman filter. Currently, there are systematic differences between the two attitude solutions that occasionally exceed the mission requirements for 3a attitude uncertainty. Attempts tounderstand and reduce these differences are continuing.
*This work was performed under National Aeronautics and Space Administration (NASA)/Goddard Space Flight Center (GSFC), under contract NAS 5-31500. This paper is declared a work of the U.S. Government and is notsubject to copyright contract in the United States.
**Computer Sciences Corporation (CSC), 10110 Aerospace Road, Lanham-Seabrook. Maryland 2.0706.
*** NASA Goddard Space Flight Center Greenbelt, Maryland 20771.