Design of Pocket-GMT: an optical emulation of the Giant Magellan Telescope
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Design of Pocket-GMT: an optical emulation of the Giant Magellan Telescope Josephine Munro1 · Marcus Lingham1 · Luke Gers1 · Nicholas Herrald1 · Tony Travouillon1 · Antonin Bouchez2 Received: 30 April 2020 / Accepted: 14 September 2020 / Published online: 6 October 2020 © Springer Nature B.V. 2020
Abstract The concept design for a laboratory based telescope emulator for the Giant Magellan Telescope (GMT) is described here. The Giant Magellan Telescope has a primary mirror comprised of 7 segments, and a secondary mirror with matching segmentation. The phasing of the GMT is a complex problem; a phasing testbed, Pocket-GMT, has been designed by a group within the Research School of Astronomy and Astrophysics at the Australian National University for the Giant Magellan Telescope Corporation. Pocket-GMT uses a novel technique to split the bending modes between a piston/tip-tilt surface and a deformable mirror. Pocket-GMT will demonstrate successful phasing of an optical miniature GMT by the planned prototype wavefront sensing systems. By reproducing the optical characteristics of the GMT on a small scale, Pocket-GMT will reduce the risk associated with the phasing system and provide a platform to test the telescopeFLs instrumentation prior to commissioning. Keywords Giant magellan telescope · Pocket-GMT · Phasing · Testbed · Active optics
1 Introduction With the increase in size and complexity of ground based astronomical telescopes, it has become conducive in some circumstances to test key functionality and components within the laboratory prior to implementation. Such work has tended to revolve around the pre-commissioning of various adaptive optics schemes including [4–6, 11, 12, 23]. In the context of the Extremely Large Telescopes currently being built that
Josephine Munro
[email protected] 1
Australian National University, Canberra, Australia
2
Giant Magellan Telescope Corporation, Pasadena, USA
290
Experimental Astronomy (2020) 50:289–302
have a primary mirror diameter larger than 20 meters, the European Southern Observatory (ESO) have commissioned the Miniscule Extremely Large Telescope (MELT) to help shape the requirements of their instruments [15]. This paper reports a concept design for a phasing testbed for another Extremely Large Telescope, the Giant Magellan Telescope (GMT), which has a primary mirror diameter of 24.5 m. It is not currently viable with modern day technologies to manufacture a monolithic primary mirror for Extremely Large Telescopes due to the upscale of cost and complexity. Therefore it is necessary for larger primary mirrors to be comprised of multiple smaller segments. The primary mirror (M1, the control surface) of GMT is made up of seven circular segments, each of them 8.4 m in diameter. As shown in Fig. 1, co-aligned to each M1 segment are seven smaller segments that make up the secondary mirror (M2). The six segments of M1 that surround the central mirror are off-axis aspherical, while the central mirror is on-axis aspherical with a hole through the centre to allo
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