Optical space telescope structures: The state of the art and future directions

Abstract

which permits observation in the infrared (IR) range. However, they operate in an extremely hostile environment, and furthermore, they must be launched into space, which means they must be able to sustain additional vibrational, thermal, and acoustic loading, and which restricts the volume to that which may be enclosed within the fairing. In both ground-based and space-based cases, in order to achieve desired optical accuracy of the reflectors, extremely precise surface tolerances -potentially of the order of nanometers -are required.The design of telescopes links many fields including optics, control, structures, and it is clear that for a successful telescope to be realised its design must be carried out at a systems level, incorporating all the necessary disciplines. The purpose of this review is to focus on the role that the structures community can play in the design of telescopes by defining the state of the art from a structural perspective. By so doing, it is hoped that future research may be more effectively informed. Telescope components and definitionsIt is first necessary to consider a broader description of the components of a telescope in order to contextualise the structural aspects. Therefore, in this section a brief introduction to the generalised structure of reflecting and refracting telescopes is provided, and key terminology and definitions are introduced. ABSTRACTFuture space telescopes will be required to have significantly greater aperture and lower areal density than is currently achievable. Gossamer spacecraft structures have been proposed as a means of achieving this, but the technologies are far from mature. A state-ofthe-art review is timely and necessary as new structural paradigms are being considered for the next generation of space telescopes. There is, however, a knowledge gap between the structural engineering community and the additional fields involved in the complete telescope system, leading to the proposal of structures which are unlikely to be launched. It is hoped that, by providing a resource by which structural engineers are made aware of the wider issues in telescope design, this review will serve to overcome this knowledge gap to facilitate productive collaboration.

De-wrinkling of pre-tensioned membranes

“…Once folded inside restricted payload volumes, they offer the highest packaging ratios of any deployable structure; and post-deployment, the mass-to-area, or "areal", density is much lower than conventional monolithic structures [1]. Correspondingly, they afford greater potential for launching sails and telescopes of ever increasing size, but after deployment the membrane must be stiffened to be effective in operation.…”

“…: (a) Schematic layout of a reflective membrane structure for use as space telescope, taken from [1]. The polygonal membrane, (i), shown here to be hexagonal, is connected to an edge structure, (ii), through tensioning cables, (iii), at its vertices.…”

Control of a Hypersegmented Space Telescope

“…Highly segmented concepts have also been introduced for ground-based telescopes [9], and other space telescope concepts with 1000 or more small segments have been proposed [10]. Membrane-based approaches have also been suggested for large lightweight space telescopes (see, e.g., the review by Santer and Seffen [11]); however, these may also require somewhat similar controls technology to provide adequate optical surface quality.…”