An apparatus and method of unified orbit and attitude control for
acquisition and maintenance techniques of multiple satellites in a
formation based on GPS input, utilizing Modern Feedback Control for
providing precise autonomous on-board orbit and attitude control. This
control system can place and maintain any satellite in its designated
location in a formation, while simultaneously providing the capability to
attain and maintain the attitude of any of the satellites in the formation
with respect to the reference `head-of-fleet` satellite. Utilizing the two
different options of GPS signal, code pseudo range for orbit determination
and control and phase pseudorange for attitude determination and control,
the relative orbit and attitude state vectors of all the satellites in the
formation is determined and modern advanced multivariable feedback control
techniques, for example, linear quadratic Gaussian/loop transfer recovery
controllers for orbit control and Sliding Controller or Lyapunov
Controller for attitude control are used to provide a unified orbit and
attitude control. The control of acquisition and maintenance for multiple
spacecraft formation flying is a tracking problem, which can be converted
into a regulator problem using the relative orbit and relative attitude
kinematics and dynamics.