The SUNRISE Telescope

With its aperture of 1 m and nearly 25 m focal length, the SUNRISE tele­scope is the lar­gest and most power­ful so­lar tele­scope that has ever left the Earth. It uses in­no­va­tive mir­ror tech­no­lo­gies, ac­tive in-flight align­ment and image sta­bi­li­za­tion sys­tems. Thanks to its high spa­tial re­so­lu­tion of less than one tenth of an arc­second, the tele­scope is ca­pable of resolving struc­tures smaller than 100 km on the so­lar sur­face.

The SUNRISE tele­scope is a Gregory-type re­flec­tor con­sis­ting of a pa­ra­bo­lic pri­ma­ry mir­ror (M1) with 2.5 meters fo­cal length and an elip­tical se­con­da­ry mir­ror (M2). These mir­rors are built into a light-weight and very stable carbon fibre struc­ture. Two plane folding mirrors (M3 and M4) behind the primary mirror re­direct the light from the tele­scope to the post­focus ins­tru­men­ta­tion (PFI) sitting piggy-back on the telescope.

Solar telescopes require special mea­sures to pro­tect their ins­tru­ments from the Sun’s ra­diation. Du­ring the ob­ser­va­tions, nearly 1 kW solar ra­di­ation is con­cen­tra­ted on a disk of about 22-mm dia­meter in the first fo­cal spot. Since the ins­tru­ments ana­lyze only a small area on the Sun, a great part of the in­co­ming light needs to be de­flec­ted to pre­vent it from da­ma­ging the ins­tru­ments. At this po­si­tion a heat re­jec­tion wed­ge (HRW) acts as field stop. Two ammonia-filled heat­pipes connect the HRW to de­di­ca­ted ra­di­ators to pre­vent the HRW from over­heating, thus avoi­ding Schlie­ren build-up, which could cause wave­front de­for­ma­tions.

The HRW has a central hole of about 2.5 mm dia­meter (about 10 % of the dia­meter of the Sun’s image). Only the light pass­ing through this hole will hit the tele­scope‘s se­con­da­ry mir­ror to be trans­mit­ted to the ins­tru­ments.

The secondary mir­ror can be ac­ti­vely con­trolled to micro­meter pre­ci­sion in or­der to pro­vide diffrac­tion-limited op­ti­cal per­for­man­ce even in va­rying en­vi­ron­men­tal con­di­tions (tele­scope ele­va­tion and chan­ging ther­mal en­vi­ron­ment due to passing over cloud decks, sea/land/ice).

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