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Proceedings Paper

Fine pointing control for a Next-Generation Space Telescope
Author(s): Gary E. Mosier; Michael Femiano; Kong Ha; Pierre Y. Bely; Richard Burg; David C. Redding; Andrew Kissil; John M. Rakoczy; Lawrence Donald Craig
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Paper Abstract

The Next Generation Space Telescope will provide at least ten times the collecting area of the Hubble Space Telescope in a package that fits into the shroud of an expendable launch vehicle. The resulting large, flexible structure provides a challenge to the design of a pointing control system for which the requirements are at the milli-arcsecond level. This paper describes a design concept in which pointing stability is achieved by means of a nested-loop design involving an inertial attitude control system (ACS) and a fast steering mirror (FSM). A key to the integrated control design is that the ACS controllers has a bandwidth well below known structural modes and the FSM uses a rotationally balanced mechanism which should not interact with the flexible modes that are within its control bandwidth. The ACS controller provides stable pointing of the spacecraft bus with star trackers and gyros. This low bandwidth loop uses nearly co-located sensors and actuators to slew and acquire faint guide stars in the NIR camera. This controller provides a payload reference stable to the arcsecond level. Low-frequency pointing errors due to sensor noise and dynamic disturbances are suppressed by a 2-axis gimbaled FSM locate din the instrument module. The FSM servo bandwidth of 6 Hz is intended to keep the guide star position stable in the NIR focal plane to the required milli-arcsecond level. The mirror is kept centered in its range of travel by a low-bandwidth loop closed around the ACS. This paper presents the result of parametric trade studies designed to assess the performance of this control design in the presence of modeled reaction wheel disturbances, assumed to be the principle source of vibration for the NGST, and variations in structural dynamics. Additionally, requirements for reaction wheel disturbance levels and potential vibration isolation subsystems were developed.

Paper Details

Date Published: 28 August 1998
PDF: 8 pages
Proc. SPIE 3356, Space Telescopes and Instruments V, (28 August 1998); doi: 10.1117/12.324507
Show Author Affiliations
Gary E. Mosier, NASA Goddard Space Flight Ctr. (United States)
Michael Femiano, NASA Goddard Space Flight Ctr. (United States)
Kong Ha, NASA Goddard Space Flight Ctr. (United States)
Pierre Y. Bely, Space Telescope Science Institute (United States)
Richard Burg, Johns Hopkins Univ. (United States)
David C. Redding, Jet Propulsion Lab. (United States)
Andrew Kissil, Jet Propulsion Lab. (United States)
John M. Rakoczy, NASA Marshall Space Flight Ctr. (United States)
Lawrence Donald Craig, NASA Marshall Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 3356:
Space Telescopes and Instruments V
Pierre Y. Bely; James B. Breckinridge, Editor(s)

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