Eigenstructure versus optimal control for decoupling

A study about how to design a control law that not only keeps following a reference attitude but also maintains attitude decoupling due to the vehicle manoeuvres has been performed. A control law was designed for a satellite launcher vehicle using eigenstructure assignment and optimal control method in order that the vehicle tracks a reference attitude and also to decouple the yaw response from roll and pitch manoeuvres and to decouple the pitch response from roll and yaw manoeuvres. It has been noticed that in order to achieve this objective it is necessary to use a linear coupled model to design the control law instead of the usual linear uncoupled model used to design the tracking control law. The design was based on a complete linear coupled model obtained from the complete vehicle non-linear model by linearisation at each trajectory point. A comparison of the system stability working with both control laws has also been performed. After all, the design was assessed with the vehicle time varying non-linear model showing a good performance and robustness. The used design method is explained and a case study for the Brazilian satellite launcher VLS is reported. By the end of the work some suggestions about how to implement this control law have also been studied. [Copyright &y& Elsevier]