Large fully retractable telescope enclosuresstill closable in strong wind

摘要

Two prototypes of fully retractable enclosures with diameters of 7 and 9 m have been built for the high-resolution solartelescopes DOT (Dutch Open Telescope) and GREGOR, both located at the Canary Islands. These enclosures protectthe instruments for bad weather and are fully open when the telescopes are in operation. The telescopes and enclosuresalso operate in hard wind. The prototypes are based on tensioned membrane between movable but stiff bows, which foldtogether to a ring when opened. The height of the ring is small. The prototypes already survived several storms, withoften snow and ice, without any damage, including hurricane Delta with wind speeds up to 68 m/s. The enclosures canstill be closed and opened with wind speeds of 20 m/s without any problems or restrictions. The DOT successfullydemonstrated the open, wind-flushing concept for astronomical telescopes. It is now widely recognized that also largefuture telescopes benefit from wind-flushing and retractable enclosures. These telescopes require enclosures withdiameters of 30 m until roughly 100 m, the largest sizes for the ELTs (Extreme Large Telescopes), which will be built inthe near future. We discuss developments and required technology for the realization of these large sizes.