|
Description:
|
Automated spacecraft docking is a concept of operations with several important
potential applications . One application that has received a great deal of attention
recently is that of an automated docking capable unmanned re -supply spacecraft . In
addition to being useful for re -supplying orbiting space stations , automated shuttles
would also greatly facilitate the manned exploration of nearby space objects , including
the Moon , near -Earth asteroids , or Mars . These vehicles would allow for longer
duration human missions than otherwise possible and could even accelerate human
colonization of other worlds . This thesis develops an optimal docking controller for an
automated docking capable spacecraft . An innovative vision -based relative navigation
system called VisNav is used to provide real -time relative position and orientation
estimates , while a Kalman post -filter generates relative velocity and angular rate estimates
from the VisNav output . The controller's performance robustness is evaluated
in a closed -loop automated spacecraft docking simulation of a scenario in circular
lunar orbit . The simulation uses realistic dynamical models of the two vehicles , both
based on the European Automated Transfer Vehicle . A high -fidelity model of the
VisNav sensor adds realism to the simulated relative navigation measurements . The
docking controller's performance is evaluated in the presence of measurement noise ,
with the cases of sensor noise only , vehicle mass errors plus sensor noise , errors in
vehicle moments of inertia plus sensor noise , initial starting position errors plus sensor noise , and initial relative attitude errors plus sensor noise each being considered .
It was found that for the chosen cases and docking scenario , the final controller was
robust to both types of mass property modeling errors , as well as both types of initial
condition modeling errors , even in the presence of sensor noise . The VisNav
system was found to perform satisfactorily in all test cases , with excellent estimate
error convergence characteristics for the scenario considered . These results demonstrate
preliminary feasibility of the presented docking system , including VisNav , for
space -based automated docking applications . |