<title>Optical pointing stability achievement through isolation</title>

Abstract

The requirements concerning optical instruments stability on satellites are getting more and more stringent. At the same time, those instruments have to put up with a disturbed dynamic environment caused by other on- board equipments which can be made worse by flexible structures. A possible design option for achieving pointing stability can consist in isolating the optical sensitive payload from the host satellite. Such a concept is being studied by CNES (french space agency) on a small angular range (+/- 5 degree(s)) payload and a laboratory breadboard of a two axis gimbal 'softmount' system has been developed using flex pivots to carry out passive isolation. The instrument's Line-of-Sight (LOS) stabilization is performed through a control algorithm using acceleration feedback and positive feedback on relative position error in order to decrease the flex pivot resonance. These informations are determined respectively by angular accelerometers and capacitive encoders mounted on each axis. Another design option consists in a 'rigid mount'. In this case the LOS stabilization is performed by a strong control on inertial position error information. This alternative is being studied using a specific optical bench to provide the inertial position error. These two concepts are limited in performance and an optimal solution has to combine both principles to achieve the demanding pointing stabilization requirements of future satellite systems. This paper presents primarily first experimental results and highlights problems encountered, such as delay or flexible modes, as well as solutions proposed.