The prescribed convergence time control issue of spacecraft with parametric uncertainty in inertia and disturbance is investigated in this paper. It is solved by presenting an adaptive sliding mode control framework. As a stepping stone, a new practical predefined-time stability theorem is presented for a class of nonlinear systems. Its maximum convergence time is independent of initial states and is explicitly prescribed via a gain determined by designers. Based on this theorem, an adaptive predefined-time sliding-mode manifold is developed. Then, a chattering-free and nonsingular predefined-time controller is designed. The spacecraft attitude dynamics’ states are governed into a tiny neighborhood with arbitrary small radius after the prescribed time. The performance of this control frame[1]work is validated through two simulation examples.