Date of Award

3-14-2014

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Electrical and Computer Engineering

First Advisor

James A. Louthain, Ph.D, PhD.

Abstract

Atmospheric turbulence causes tilt distortion that requires telescopes to track and remove image jitter effects. This research develops an adaptive tilt tracking system to measure and compensate for centroid gain volatility while tracking extended objects. The adaptive tracker counteracts deviations in tilt measurement and correction, due to unintended centroid gain changes. Non-adaptive trackers experience sub-optimal bandwidths and possible instabilities. The adaptive tracker utilizes a quadrant (QUAD) cell tilt detector to measure tilt distortion and its centroid gain relates measured intensity imbalances amongst the four cells to tilt distortion. Additionally, this gain becomes a random variable as it is determined by random image spot characteristics. The tracked LEO object and atmospheric seeing govern spot characteristics. This research develops an innovative methodology that rotates the LEO object's image to create a more favorable intensity distribution for the QUAD-cell. Along with image rotation, an adaptive gain term yields significant improvements in QUAD-cell measurement performance, up to 91% for the simulated tilt processes. Using the image rotation and adaptive gain methodology, this research realizes an adaptive tilt tracker model that dithers the fast steering mirror to detect non-optimal centroid gains. Results show the adaptive tracker effectively counteracts centroid-gain deviations.

AFIT Designator

AFIT-ENG-14-M-78

DTIC Accession Number

ADA613029

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