Design of the Deployment Mechanism for the Primary Mirror Elements of a Deployable Space Telescope

Abstract

Applications for space telescopes require ever higher resolutions. This is driving space telescopes to keep getting bigger as they need a large primary mirror to achieve these resolutions. Such large instruments are also heavy and cost a lot of money to launch. Current launchers offer a limited amount of space making it impossible to launch a telescope with a monolithic mirror larger than five meters in diameter. Over the last few decades, the interest in utilizing segmented deployable mirrors in order to achieve larger effective apertures has steadily increased. The Space Systems Engineering department of the faculty of Aerospace Engineering at the TU Delft started working on a deployable synthetic aperture telescope in 2014 and is now continuing the research in cooperation with ESA, TNO and ADS. The optical design of the Deployable Telescope System (DTS) is already in an advanced stage. However, much work remains to be done. One of the main challenges is designing a highly accurate and stable deployment mechanism for the primary mirror elements of this instrument. Position and orientation tolerances for the primary mirror elements have been determined in a previously performed top down systems engineering approach. The most critical requirements are on the piston and tilt of the mirrors. The required piston and tilt accuracies of each mirror element are 2[μm] and 2[μrad] respectively. The key to achieving accurate deployment is to separate the deployment motion into a course deployment of the mirror segments, followed by a separate fine calibration stage that allows for accurate tip, tilt and piston control. From the literature study that precedes this thesis proposal, it was concluded that it is a challenging task to design a deployment mechanism for the deployable telescope that can offer sufficient accuracy. The goal is to design the mechanism such that it is reliable, lightweight and suitable to the current optical design. The design should allow for the mirror segments to be folded close to the telescope body so that the stowed instrument fits within a minimal envelope. This thesis covers the design process for the deployment mechanism for the primary mirror elements of the telescope. Successfully designing a deployment mechanism with all these qualities will be a big step forward in realizing the DTS. Due to the deployable design, this telescope can be an order of magnitude less heavy and requires a lot less space inside a launcher when compared to current telescopes. The concept will also allow for the development of telescope mirrors much larger than five meters in diameter.