Active optics for next generation of space observation instruments

Abstract

Thales Alenia Space has been involved in the design and the development of space observation instruments for over 40 years. This paper will explain why active optics is needed for next generation of instruments for Earth observation. We will also describe what kind of solution is preferred and why. We will give an overview of the development status on the associated technologies. Indeed, the future missions will have to deal with better performance, better optical quality while from manufacturing point of view, the total mass, the development schedule and the final cost have to be reduced. These constraints induce a new generation of solutions based on large entrance optics associated to high lightweight ratio which naturally provide solutions sensitive to gravity deformation. In these conditions, the enhancement of the final performance can only be guaranteed by using active optics in flight. A deformable mirror is therefore foreseen to be implemented in future large telescopes in order to correct manufacturing residues, ground/flight evolution including gravity. Moreover, low mass and low cost require more compact designs which entail solutions more sensitive to misalignment. An active positioning mechanism is then also needed in order to correct the telescope alignment during operation conditions. Thales Alenia Space has been selected by CNES to develop and qualify active optics building blocks and then to test and demonstrate the improvement that new active technologies can bring in a full size instrument representative of the next generation of observation instruments. An overview of the current development status and the achievable performances is given.

Active lens and mirror technology through tailored thermal expansion

“…3 The application range for active optics varies from complex camera lenses to laboratory equipment for shaping wavefronts to exact specifications. 2,4,5 There has been some excellent advances in this field through the development of various systems that fulfil such needs, such as piston driven fluid lenses, 6 liquid crystal lenses, 7 and microfluidics. 8 There are also solutions for actively controlled mirror components such as piezo stack driven deformable mirrors which find their use in adaptive optics within ground based astronomical observation.…”

“…Similarly an array of deformable mirrors could find their use in adaptive optics for a tuneable mirror to correct for atmospheric disturbances as well as earth observation. 5 The structures in the mirror array can be completely continuous which is possible from the indirect heating via the layer separating method for creating individual elements.…”

Full scale active telescope engineering model

“…Thales Alenia Space France has developed an end-to-end design philosophy, combining the choice of the most suited technology for the Primary Mirror, the active components (MM2 and Madras), the wave-front sensing element, together with an end-to-end software taking into account all parameters. The active telescope design rationales for Extremely High Resolution in Earth observation have been developed in [1]. The variations of attitude during the orbit lead to thermal flux variations.…”