  This paper investigates the attitude control problem of spacecraft, with the
objective of achieving precise performance criteria including precise settling
time, steady-state error, and overshoot elimination. To tackle this challenge,
we propose the Precisely-Assigned Performance (PAP) control scheme. Firstly, we
utilize a parameterized function to explicitly characterize a reference for the
transient responses, termed the Reference Performance Function (RPF).
Subsequently, leveraging the concept of the RPF, we define a
performance-satisfied tube region and introduce the concept of control barrier
functions to derive a sufficient condition for the state trajectory to converge
and remain confined within this tube region. By introducing the concept of
Sontag's universal formula for stabilization, a PAP controller, constructed
based on the backstepping method, is then designed to guide the system to
satisfy these affine constraint conditions, and a disturbance observer is
further integrated to handle perturbations. Theoretical proofs are presented to
demonstrate the controller's capability to establish the boundedness of the
overall system and ensure that each state trajectory will converge into the
performance-satisfied region within a finite time duration under any
conditions. Finally, numerical simulation results are presented to validate the
effectiveness of the proposed method.
