For WST to deliver the exceptional quality and quantity of science data demanded by the astronomy community, the Telescope and Instruments must be designed as an integrated system with the Enclosure and surrounding Infrastructure providing the support to enable efficient operation in an environmentally sustainable manner.

Telescope design

The telescope is deemed to simultaneously provide two distinct, seeing-limited focal surfaces. An alt-az mount is the most plausible kinematic arrangement. The 11-m class primary mirror will be segmented. With a view to mitigating cost and risks, optomechanical subunits (e.g. primary and secondary mirror units) would remain within the technological boundaries, which are demonstrated with the ELT. For example, the specification for the WST primary mirror segment assemblies, including supports and controls, could be nearly identical to that of the ELT - thereby simplifying design, development, production and operation considerably. Local control strategies would also duplicate ELT solutions to the maximum possible extent. Compensation of atmospheric turbulence being ruled out - at least for the largest of the two fields -, wavefront control ought to cover low spatial and temporal frequencies only, à la VLT.

At system level, the telescope is bound to respond to specific instrumentation requirements. Ideally, it will have to accommodate large instrument volumes in a dimensionally stable environment, while retaining sufficient structural stiffness to mitigate external perturbations - e.g. wind buffeting - and while retaining a compact dome design.

The optical solution is till open and several alternatives are being explored, with either refracting or reflecting field correctors. For historical reference we show on the right the design of a compact 11 m aperture telescope concept (Pasquini et al, 2017) with a MOS at the Cassegrain focus (5 square degrees field of view) and the IFS at the Coude focus.