The drift rates of the attitude control gyros on the Viking Orbiters were calibrated several times in flight. The process by which these rates were estimated as functions of time is novel for a space flight project, although relatively standard estimation techniques were used. The process is described fully and the results obtained from the twelve Viking single-axis gyros are analyzed. Although the possibility was explored, no significantly repeatable function of drift rate vs time or temperature was discovered; the overall mean was found to predict drift rate with acceptable accuracy.
The utility of autonomous navigation for spacecraft operations is examined to define the related critical issues facing a spacecraft designer. From the various means available, relative navigation to other spacecraft, especially to GPS, is shown as the most cost-effective near-term means of approaching the goals of autonomous navigation, without necessarily achieving real autonomy. The latter will evolve with our confidence in artificial intelligence technology as an essential prerequisite to truly autonomous spacecraft operation, including the navigation task.
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