Reduced-Effort Control Laws for
Underactuated Rigid Spacecraft
Recent results show that a nonsmooth, time-invariant
feedback control law can be used to
rotate an axi-symmetric rigid spacecraft to the zero equilibrium using
only two control torques.
This method, however, may require a significant amount
of control effort, especially for initial conditions close to
an equilibrium manifold corresponding to rotations about the unactuated
principal axis.
In this paper a control law is proposed which
reduces the control effort required to perform rest-to-rest maneuvers
for initial conditions close to this equilibrium manifold.
Specifically, the phase space of the system is divided into two parts, one
corresponding to initial conditions producing large control effort (the
``bad'' region) and
the other corresponding to initial conditions producing small control
signals (the ``good'' region).
The proposed control law then renders this undesirable
equilibrium manifold unstable
driving the trajectories of the closed-loop system into the ``good'' region,
where the original control law is subsequently used.
Numerical simulations indicate reduction of the control magnitude at the
order of 80-90 \% for initial conditions close to the equilibrium
manifold.
Full paper postscript version (253K).
Click here
return to main homepage.