Trade-off for very large space telescope mirrors

The objective is to perform an assessment of feasibility and a trade-off at system-level for the implementation of large space telescopes in future science (and Earth observation) payloads fully in line with the needs identified by the Future Technology Advisory Panel (FTAP). Roadmaps shall be established for the various options for the development and manufacturing of such telescopes.

Currently the size limit for primary mirrors of large telescopes is - due to the available Ariane-5 fairing - typically at 3.5m (Herschel). Future science (and most likely also Earth observation missions) will call for larger telescope sizes due to more demanding requirements on the light collecting efficiency and angular resolution. Different possibilities can be envisaged to increase the size of telescopes:- maximising the diameter of the rotational symmetric monolithic primary mirror compatible with the dimension of existing launcher fairings;- maximising the size of an off-axis elliptical primary mirror by making best use of existing launcher fairing volumes most likely in combination with an unfoldable secondary mirror;- introducing a segmented primary mirror that will be deployed in-orbit (like JWST) using existing fairings;- increasing the size of a monolithic mirror assuming a larger fairing (diameter 8m) will be available.System designs shall be established and traded-off to identify the most suitable design and approach for extending the light collection efficiency and angular resolution of large space telescopes. The trade-off shall include design complexity, risk and manufacturing cost. The primary mirror of the selected concept shall be designed in line with typical environmental and performance requirements. Roadmaps for all feasible implementation solutions shall be established for the development of such a mirror. Development needs for manufacturing and testing facilities shall be identified.Two parallel studies shall be implemented. Multi-disciplinary cooperation with support from mechanisms and structure experts will be implemented for the execution of this activity.