Modelling and control of satellite formations

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Title: Modelling and control of satellite formations
Author: Vaddi, Veera Venkata Sesha Sai
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 .
URI: http : / /hdl .handle .net /1969 .1 /329
Date: 2004-09-30


Modelling and control of satellite formations. Available electronically from http : / /hdl .handle .net /1969 .1 /329 .

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