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Description:
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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 . |