Jorge E. Diaz

Date of Award

3-24-2016

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Electrical and Computer Engineering

First Advisor

Scott J. Pierce, PhD.

Abstract

In order for celestial navigation observing satellites to provide accurate positioning estimates, precise ephemerides of the observed satellites are necessary. This work analyzed a method to correct for satellite ephemeris to be used in celestial navigation applications. This correction is the measured angle differences between the expected location of the satellite, which is given by propagating publicly available Two-Line Elements (TLE), and their observed angles from a precisely known reference site. Therefore, the angle difference can be attributed completely to satellite ephemeris error assuming instrument error was accounted for. The intent is to calculate this correction from the reference site and relate it to remote sites that have visibility of the same satellite, but where its own location is known with some uncertainty. The effects of increased baseline distances from the reference site, in addition to time delays when the correction was calculated are studied. Satellite observations were simulated and propagated using TLEs. This simulated data was manipulated to calculate the angle difference and transform that angle to the viewpoint of the remote sites. This corrected observed angle was integrated using an extended Kalman Filter (EKF) with an inertial measurement unit (IMU) and a barometric altimeter. The performance of the position solution in the navigation filter was calculated as the error from simulated truth. The satellite ephemeris error measured at a reference location becomes less observable by a remote user according to the line-of-sight transformation due to the reference-satellite-remote geometry. A mathematical formula for calculating the applicability of projecting the remote site observation to other locations is developed and compared to simulated ephemeris errors. This formula allows a user to define geographic regions of validity through ephemeris error tolerance. Estimating the ephemeris error with regular updates from a reference site resulted in a reduction of inertial measurement unit (IMU) drift and reducing the distance root mean squared (DRMS) error by a maximum of 98% under certain conditions.

AFIT Designator

AFIT-ENG-MS-16-M-013

DTIC Accession Number

AD1053802

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