|dc.contributor.advisor||Bishop, Robert H., 1957-||en
|dc.creator||Crain, Timothy Price, 1973-||en
|dc.description.abstract||This work documents the development of a real-time interplanetary orbit determination
monitoring algorithm for detecting and identifying changes in the spacecraft
dynamic and measurement environments. The algorithm may either be utilized
in a stand-alone fashion as a spacecraft monitor and hypothesis tester by navigators
or may serve as a component in an autonomous adaptive orbit determination architecture.
In either application, the monitoring algorithm serves to identify the orbit
determination filter parameters to be modified by an offline process to restore the
operational model accuracy when the spacecraft environment changes unexpectedly.
The monitoring algorithm utilizes a hierarchical mixture-of-experts to regulate
a multilevel bank organization of extended Kalman filters. Banks of filters operate
on the hierarchy top-level and are composed of filters with configurations representative
of a specific environment change called a macromode. Fine differences,
or micromodes, within the macromodes are represented by individual filter con-
figurations. Regulation is provided by two levels of single-layer neural networks
called gating networks. A single top-level gating network regulates the weighting
among macromodes and each bank uses a gating network to regulate member filters
Experiments are conducted on the Mars Pathfinder cruise trajectory environment
using range and Doppler data from the Deep Space Network. The experiments
investigate the ability of the hierarchical mixture-of-experts to identify three environment
macromodes: (1) unmodeled impulsive maneuvers, (2) changes in the solar
radiation pressure dynamics, and (3) changes in the measurement noise strength.
Two methods of initializing the gating networks are examined in each experiment.
One method gives the neurons associated with all filters equivalent synaptic weight.
The other method places greater weight on the operational filter initially believed
to model the spacecraft environment. The results will show that the equal synaptic
weight initialization method is superior to the one favoring the operational filter and
that processing range and Doppler data together is superior to processing Doppler
data alone. When processing range and Doppler with an equally initialized hierarchy,
all three macromodes are definitively identified by the top-level gating network
weights. Additionally, in the case of multiple successive macromode changes, the
hierarchy is generally able to recover from one macromode and identify a change
to another macromode.||
|dc.rights||Copyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.||en
|dc.title||Adaptive interplanetary orbit determination||en
|dc.description.department||Aerospace Engineering and Engineering Mechanics||en
|thesis.degree.department||Aerospace Engineering and Engineering Mechanics||en
|thesis.degree.grantor||The University of Texas at Austin||en
|thesis.degree.name||Doctor of Philosophy||en