PULSAR: development of a mirror tile prototype for future large telescopes robotically assembled in space

Abstract

The H2020 project PULSAR (Prototype for an Ultra Large Structure Assembly Robot) development objective is to create three demonstrators that that will pave the way for the construction of large structures in orbit. The study case considered in PULSAR is the assembly of a segmented primary mirror for next generation 35m space-based telescope. In the frame of this project, CSEM is developing Single Mirror Tile demonstrators (SMT) that host a positioning mechanism capable of adjusting the position of the hexagonal mirror in order to compensate for inaccuracies generated by the robotic assembly. This mechanism has a tripod architecture. It is composed of three linear actuators and of transmission stages, each made of a flexible pivot and of a gimbal. This mechanism allows for controlling the mirror position along three degrees of freedom (piston translation and tip and tilt rotations). The piston stroke is required to be ±3 mm with a resolution of 1 µm and a repeatability better than 5 µm while the tip/tilt strokes are ±1° with 4 µrad of resolution and 20 µrad of repeatability. The design of the tiles benefits from CSEM extensive experience in compliant mechanisms and additive manufacturing applied to the domain of scientific instrumentations for space applications.