The Next Generation Space Telescope. Proposed Pointing Control System
B. Scott May, Grad. Student, Option in Civ. Engrg., Calif. Inst. of Tech.
Pasadena, CA 91125; formerly, Dept. of Civ. Engrg., The Johns Hopkins Univ.,
Baltimore, MD 21218-2686, Student Member ASCE
and Nicholas P. Jones, Assoc. Prof., Dept. of Civ. Engrg., The Johns Hopkins
Univ., Baltimore, MD 21218-2686, A.M. ASCE.
Abstract:
The pointing control system of the Hubble Space Telescope (HST) represents the
current state-of-the-art for the precision control of a large spacecraft. The
proposed Next Generation Space Telescope (NGST) will require an
order-of-magnitude increase in pointing resolution over that of HST. The use
of active optics in the form of a steerable secondary mirror has been proposed
for NGST to satisfy these requirements. The primary motivation for this study
was to demonstrate the feasibility of satisfying the pointing-stability
requirements by sensing the guide star position and steering the optical path
of the telescope with the active secondary mirror. To study the requirements of
the control system, a two-degree-of-freedom model which retains the rigid-body
mode of the telescope as well as its first oscillatory mode was constructed.
The corresponding optimal control law was developed and implemented in a
discrete manner to examine the behavior of the system subject to typical
spacecraft excitations.