| dc.description.abstract | Formation flying is a new paradigm in space mission design,
aimed at replacing large satellites with multiple small
satellites. Some of the proposed benefits of formation flying
satellites are: (i) Reduced mission costs and (ii) Multi mission
capabilities, achieved through the reconfiguration of formations.
This dissertation addresses the problems of initiatialization,
maintenance and reconfiguration of satellite formations in Earth
orbits. Achieving the objectives of maintenance and
reconfiguration, with the least amount of fuel is the key to the
success of the mission. Therefore, understanding and utilizing the
dynamics of relative motion, is of significant importance.
The simplest known model for the relative motion between
two satellites is described using the Hill-Clohessy-Wiltshire(HCW)
equations. The HCW equations offer periodic solutions that are of
particular interest to formation flying. However, these solutions
may not be realistic. In this dissertation, bounded relative orbit
solutions are obtained, for models, more sophisticated than that
given by the HCW equations. The effect of the nonlinear terms,
eccentricity of the reference orbit, and the oblate Earth
perturbation, are analyzed in this dissertation, as a perturbation
to the HCW solutions. A methodology is presented to obtain initial
conditions for
formation establishment that leads to minimal maintenance effort.
A controller is required to stabilize the desired relative
orbit solutions in the presence of disturbances and against
initial condition errors. The tradeoff between stability and fuel
optimality has been analyzed for different controllers. An
innovative controller which drives the dynamics of relative motion
to control-free natural solutions by matching the periods of the
two satellites has been developed under the assumption of
spherical Earth. A disturbance accommodating controller which
significantly brings down the fuel consumption has been designed
and implemented on a full fledged oblate Earth simulation. A
formation rotation concept is introduced and implemented to
homogenize the
fuel consumption among different satellites in a formation.
To achieve the various mission objectives it is necessary
for a formation to reconfigure itself periodically. An analytical
impulsive control scheme has been developed for this purpose. This
control scheme has the distinct advantage of not requiring
extensive online optimization and the cost incurred compares well
with the cost incurred by the optimal schemes. | en |
