Progress of ESO's 100-m OWL optical telescope design

Abstract

Even as a number of 8-to 10-m class telescopes come into operation worldwide, the scientific challenges these instruments and their space-based counterparts already address imply that future increases in lightgathering power and resolution will have to exceed conventional scaling factors. Indeed, it can be exp ected that the same progress in telescope diameter and resolution achieved throughout the century must now be realized within, at most, one or two decades. The technologies required to assert the validity of such an extrapolation appear to be within reach. Large telescopes successfully commissioned within the last decade have demonstrated key technologies such as active optics and segmentation. Furthermore, current design methods and fabrication processes imply that the technological challenge of constructing telescopes up to the 100-m range could, in some critical areas, be lower than those underlying, two decades ago, the design and construction of 8 -to 10-m class telescopes. At system level, however, such giants are no size-extrapolated fusion of VLT and Keck, but fully integrated adaptive systems. In this paper we elaborate on some of the science drivers behind the OWL concept of a 100-m telescope with integrated adaptive optics capability. We identify major conceptual differences with classical, non-adaptive telescopes, and derive design drivers accordingly. We also discuss critical system and fabrication aspects, and the possible timeline for the concept to be realized.

Future giant telescopes: integration of MCAO into telescope design

“…Assuming that the reliability issue is resolved, we consider two families of designs based on two-mirror basic configurations: Ritchey-Chrétien and aplanatic Gregorian systems. Many variants of such two-mirror telescopes exist with apertures of 8-10 m. Current ELT projects [3][4][5][6][7][8][9] feature similar twomirror basic configurations, except for the European ELT and OWL designs [2,10]. One of the reasons for high popularity of the two-mirror designs is their relatively straightforward configurability to provide gravity stable foci on the Nasmyth platforms, which are essential for many science instruments.…”

“…Recent advances in adaptive optics (AO) [1] allowed astronomers to improve the angular resolution of existing telescopes by reducing the atmosphere-induced blurring effects. The current plans for building the future extremely large telescopes (ELTs) [2][3][4][5][6][7][8][9][10] featuring multi-conjugate AO (MCAO) systems [11][12][13][14][15][16][17][18][19][20] are justified by their potential to reach the diffraction limit over an extended field of view (FoV) with the resolution of a few milliarcseconds. Current difficulties in manufacturing large deformable mirrors (DMs) limit their direct use in the main telescope system [21].…”

OWL phase A status report

“…The optical design of OWL [5] is based on a 6-mirror solution, with spherical primary, flat secondary, and a fourelements corrector. The total field of view is limited by rapidly increasing vignetting beyond 10 arc minutes field diameter.…”

Properties of Zerodur mirror blanks for extremely large telescopes

“…Thereby one has to consider that a telescope like OWL with a primary mirror diameter of 100 m represents a collection area of seven times the total collecting area of every optical telescope ever built 13 . The cost estimation for the OWL project is almost 1 billion Euros in capital investment for the final design and construction 14 . So the discussed large astronomical projects have to handle extreme technical challenges, but also an enormous budget and a high economical risks.…”