Correlation Tracking for a Planetary Pointing and Tracking System

Abstract

The Planetary Pointing and Tracking System (PPTS) being developed at Jet Propulsion Laboratory is intended to provide precision pointing for science platforms on future autonomous planetary spacecraft. Future missions will impose very stringent platform pointing requirements due to low light levels and very high ground tracking rates. An integral part of PPTS is the correlation tracker, which has the potential to revolutionize autonomous guidance. The tracker provides two-axis pointing information concerning the position of the target body. It consists of a large-area charge-coupled device (CCD) imager and a microprocessor to control the CCD scanning function and data processing. The correlation tracker has three modes of operation: track, acquire and map. The track mode performs precision tracking of a target object. This is initiated after a target has been acquired. The map mode determes the centroidal coordinates, magnitude and size of bodies within the optical field of view. To improve precision pointing, various power spectra, such as shot noise and dark current, are derived. The probability of acquiring a target body is a function of signal-to-noise ratio and the noise equivalent angle. Derivations illustrating the application of these concepts are given. A discussion of mission analysis with the Uranian system as a representative example is provided.