  This paper deals with the dynamics and controls of a quadrotor unmanned
aerial vehicle that is connected to a fixed point on the ground via a tether.
Tethered quadrotors have been envisaged for long-term aerial surveillance with
high-speed communications. This paper presents an intrinsic form of the dynamic
model of a tethered quadrotor including the coupling between deformations of
the tether and the motion of the quadrotor, and it constructs geometric control
systems to asymptotically stabilize the coupled dynamics of the quadrotor and
the tether. The proposed global formulation of dynamics and control also avoids
complexities and singularities associated with local coordinates. These are
illustrated by numerical examples.
