Giant Segmented Mirror Telescope (GSMT) Structure – A Conceptual Design

January 30, 2003

The Giant Segmented Mirror Telescope (GSMT) is a 30-m fully-steerable ground-based optical/infra-red telescope with actively controlled segmented mirrors. This paper presents the initial point design for the telescope structure which was used to evaluate the expected structural behavior needed in developing other aspects of the telescope design, in particular, the adaptive optics system. The primary mirror consists of 618 hexagonal 1.152-m mirror segments supported on 91 rafts. A typical raft supports seven mirror segments. There are two level of actuation; each mirror segment is supported by actuators mounted on the raft structure and each raft is supported by another level of actuators mounted on the elevation structure. A radio telescope-type design is used for its structural advantages as well as for accommodation of large instruments. In particular, the location of the elevation bearings allows for an efficient support of the primary and a smaller azimuth structure. The elevation structure consists of (1) a space truss backstructure that supports the rafts, (2) a braced tripod structure that supports the prime focus instrument or secondary mirror, and (3) the transition structure and elevation wheel that connect the backstructure to the elevation bearings and provide support for the drive arc and the counterweight. The azimuth structure accommodates a large Nasmyth platform. Issues covered in this paper include: natural frequencies, response to wind buffeting, deflection limits to accommodate actuator strokes, span between elevation bearings, braced tripod to minimize blockage, and configuration to maximize space for instruments.

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