This paper proposes an explicit reference governor-based control scheme
for the velocity-free spacecraft attitude maneuver problem subject to
the pointing constraint, the angular velocity constraint, and the input
constraint. The proposed two-layer control scheme guarantees asymptotic
stability of the attitude while satisfying the aforementioned
constraints. The inner layer relies on output feedback control via an
immersion and invariance technology-based angular velocity observer,
enabling attitude stabilization without measuring angular velocity. By
analyzing the geometry of the pointing constraint, the upper bound of
the angular velocity, and the optimization solution of the control
input, the safety boundary described by the invariant set is obtained in
the reference layer. Additionally, we introduce the dynamic factor
related to the angular velocity estimation error into the invariant set
to prevent states from exceeding the constraint set due to unmeasurable
angular velocity information. The shortest guidance path is then
designed in the reference layer. Finally, we verify the effectiveness of
the proposed constrained attitude control algorithm through numerical
simulations.