  This paper focuses on the design of a stabilizing control law for an aerial
vehicle which is physically connected to a ground station by means of a tether
cable. By taking advantage of the tensile force acting along the taut cable, it
is shown that the tethered UAV is able to maintain a non-zero attitude while
hovering in a constant position. The control objective is to stabilize the
desired configuration while simultaneously ensuring that the cable remains taut
at all times. This leads to a nonlinear control problem subject to constraints.
This paper provides a two-step solution. First, the system is stabilized using
a cascade control scheme based on thrust vectoring. Then, constraint
satisfaction is guaranteed using a novel Reference Governor scheme.
