The Magellan Telescopes are a set of twin 6.5 meter ground based optical/near-IR telescopes operated by the Carnegie Institution for Science at the Las Campanas Observatory (LCO) in Chile. The primary mirrors are f/1.25 paraboloids made of borosilicate glass and a honeycomb structure. The secondary mirror provides both f/11 and f/5 focal lengths with two Nasmyth, three auxiliary, and a Cassegrain port on the optical support structure (OSS). The telescopes have been in operation since 2000 and have experienced several small earthquakes with no damage. Measurement of <i>in situ</i> response of the telescopes to seismic events showed significant dynamic amplification, however, the response of the telescopes to a survival level earthquake, including component level forces, displacements, accelerations, and stresses were unknown. The telescopes are supported with hydrostatic bearings that can lift up under high seismic loading, thus causing a nonlinear response. For this reason, the typical response spectrum analysis performed to analyze a survival level seismic earthquake is not sufficient in determining the true response of the structure. Therefore, a nonlinear transient finite element analysis (FEA) of the telescope structure was performed to assess high risk areas and develop acceleration responses for future instrument design. Several configurations were considered combining different installed components and altitude pointing directions. A description of the models, methodology, and results are presented.
The preliminary design of the 25 m Giant Magellan Telescope (GMT) has been completed. This paper describes the design of the optics, structure and mechanisms, together with the rationales that lead to the current design. Analyses that were conducted to verify structure and optical performance are summarized. Science instruments will be mounted within the telescope structure. A common instrument de-rotator is provided to compensate for field rotation caused by the alt-az tracking of the telescope. The various instrument stations and provisions for mounting instruments are described. Post-PDR development plans for the telescope are presented.
The Giant Magellan Telescope (GMT) is an optical-infrared 25 Meter ELT to be located in Chile. It is being designed and constructed by a group of U.S. and international universities and research institutions. The Gregorian Instrument Rotator (GIR) for GMT will be a structural-mechanical assembly 9.4 meters in diameter and 6.9 meters long. The complete assembly including structure, instruments and mechanisms has a rotating mass of 117,000 kg. It will be supported by a unique bearing system using high-capacity precision industrial rollers. The rollers will support the GIR via two large hardened and ground runner bearings integral with the structure. The bearing system includes an upper axial bearing with (8) rollers and an upper and lower radial bearing, each using (10) identical rollers. The bearing system will have the advantages of adjustability, low friction, low noise (jitter), and low cost. The rollers have a manufacturer-rated capacity 4 times greater than their maximum working load in GMT. It is important that the hardened runner bearings have a life in this application comfortably greater than the life of the GIR in the telescope. A test was devised and executed to confirm the life of the runner bearing surface (track) and to characterize the bearing friction. The bearing system design and test details and results are described.
We describe the Michigan/Magellan Fiber System (M2FS) under construction for use on the Magellan/Clay telescope.
M2FS consists of four primary components including: (1) A fiber-fed double spectrograph (MSPec) in which each
spectrograph is fed by 128 fibers (for a total multiplexing factor of 256) and each is optimized in to operate from 370-
950 nm; (2) A fiber mounting system (MFib) that supports the fibers and fiber plug plates at the telescope f/11 Nasmyth
focal surface and organizes the fibers into ‘shoes’ that are used to place the fibers at the image surface of the MSpec
spectrographs;, (3) A new wide-field corrector (WFC) that produces high-quality images over a 30 arcmin diameter
field; (4) A unit (MCal) mounted near the telescope secondary that provides wavelength and continuum calibration and
that supports a key component in a novel automated fiber identification system. We describe the opto-mechanical
properties of M2FS, its modes of operation, and its anticipated performance, as well as potential upgrades including the
development of a robotic fiber positioner and an atmospheric dispersion corrector. We describe how the M2FS design
could serve as the basis of a powerful wide-field, massively multiplexed spectroscopic survey facility.
The Giant Magellan Telescope (GMT), one of several next generation Extremely Large Telescopes (ELTs), is a 25.4
meter diameter altitude over azimuth design set to be built at the summit of Cerro Campanas at the Las Campanas
Observatory in Chile. The primary mirror consists of 7 individual 8.4 meter diameter segments resulting in an equivalent
collecting area of a 21.5 meter diameter single mirror. The telescope structure, optics and instrumentation has a rotating
mass of approximately 1250 metric tons and stands approximately 40 meters tall. This paper reports the results of our
ongoing preliminary design and development of the GMT structure and its major mechanical and opto-mechanical
components. A major recent redesign of the Gregorian Instrument Rotator (GIR) resulted in significant changes to the
telescope structure and several mechanisms. Design trade studies of various aspects of the main structure, hydrostatic
bearing system, main axes drives, M2 positioner, M3 subsystem and the corrector-ADC subsystem have refined the
preliminary design in these areas.
The Giant Magellan Telescope (GMT) is an optical-infrared 25 Meter ELT to be located in Chile. It is being designed
and constructed by a group of U.S. and international universities and research institutions<sup>1</sup>.
Structural performance of large telescopes can be enhanced significantly with the added stiffness that results from
distributing loads to many points in the structure. In defining the two rotating assemblies in an altitude-over-azimuth
mount more than a kinematic set of constraints can lead to hydrostatic bearing oil film failure due to unintended forces
that result from runner bearing irregularities. High Frequency Over Constraint (HFOC) increases stiffness without risk of
oil film failure. It was used successfully on the Magellan 6.5 Meter Telescopes.
GMT will employ this and two additional methods to enhance stiffness at frequencies from DC wind up through the
telescope primary mode frequencies of ~11 Hz. This will be achieved without excessive hydrostatic bearing pad forces.
Detailed discussion of GMT's hydrostatic constraints, azimuth track and optics support structure (OSS) runner bearing
illustrations, and performance criteria are provided for the design.
The Giant Magellan Telescope (GMT) Mirror cells provide positioning, support, with active optics compensation, and
thermal control of the seven 8.4 meter primary mirror segments. Each mirror cell is a large steel welded structure, and in
the case of the outer off axis segments, is designed to be interchangeable for any one of the 6 possible mirror positions.
The mirror support and active optics compensation are provided through a series of single axis and three axis pneumatic
actuators that control the force used to support the mirror at a total of 165 positions and allows for support of the mirror
in any one of the six positions. Mirror positioning is provided by a stiff hexapod actuator system between the mirror and
the mirror cell. Mirror thermal control is provided by a series of fans that pressurize the mirror cell and condition the air
before it is directed into the mirror through 1700 nozzles.
The Giant Magellan Telescope (GMT) is a 21.5-meter equivalent aperture optical-infrared ELT to be located in Chile. It is
being designed and constructed by a group of U.S. and international universities and research institutions<sup>1</sup>.
The concept design of the telescope structure was summarized in an earlier SPIE paper<sup>2</sup> and described in greater detail in the
GMT Conceptual Design Review document<sup>3</sup>. The structure design has matured during the current Design Development Phase.
Important among design improvements has been optimization of the secondary truss with the goal of significantly reducing
telescope pointing errors due to wind loading. Three detailed structural changes have resulted in calculated pointing error
reductions of ~30%. The changes and their contributions to the improved performance as well as other tested features are
Additional refinements to the structure include the instrument mounting system, with a stationary folded-instrument platform
plus Gregorian Instrument Rotator utilizing hydrostatic bearings. More detailed features, such as revised C-ring bracing to
improve instrument access, are described.
PANIC (Persson's Auxiliary Nasmyth Infrared Camera) is a near-infrared
camera designed to operate at any one of the f/11 folded ports of the 6.5m Magellan telescopes at Las Campanas Observatory, Chile. The instrument is built around a simple, all-refractive design that reimages the Magellan focal plane to a plate scale of 0.125"/pixel onto a Rockwell 1024x1024 HgCdTe detector. The design goals for PANIC included excellent image quality to sample the superb seeing measured with the Magellan telescopes, high throughput, a relatively short construction time, and low cost. PANIC has now been in regular operation for over one year and has proved to be highly reliable and produce excellent images. The best recorded image quality has been ~0.2" FWHM.
A concept design has been developed for the Giant Magellan Telescope (GMT). The project is a collaboration by a group of U.S. universities and research institutions to build a 21.5-meter equivalent aperture optical-infrared telescope in Chile. The segmented primary mirror consists of seven 8.4-meter diameter borosilicate honeycomb mirrors that will be cast by the Steward Observatory Mirror Laboratory. The fast primary optics allow the use of unusually compact telescope and enclosure structures. A wide range of secondary trusses has been considered for the alt-az mount. The chosen truss employs carbon fiber and steel and, due to its unique geometry, achieves high stiffness with minimal wind area and primary obscuration. The mount incorporates hydrostatic supports and a C-ring elevation structure similar in concept to those implemented on the Magellan 6.5-m and LBT dual 8.4-m telescopes. Extensive finite element analysis has been used to optimize the telescope structure, achieving a lowest telescope resonant frequency of ~5 Hz. The design allows for removal and replacement of any of the 7 subcells for off-telescope mirror coating with no risk to the other
mirrors. A wide range of instruments can be used which mount to the top or underside of a large instrument platform below the primary mirror cells. Large instruments are interchanged during the day while small and medium-sized instruments can be enabled quickly during the night. The large Gregorian instruments will incorporate astatic supports to minimize flexure and hysteresis.
The Magellan Inamori Kyocera Echelle (MIKE) is a double echelle spectrograph designed for use at the Magellan Telescopes at Las Campanas Observatory in Chile. It is currently in the final stages of construction and is scheduled for commissioning in the last quarter of 2002. In standard observing mode, the blue (320-480 nm) and red (440-1000 nm) channels are used simultaneously to obtain spectra over the full wavelength range with only a few gaps in wavelength coverage at the reddest orders. Both channels contain a three-group set of all-spherical, standard optical glass and calcium fluoride lenses which function as both camera and collimator in a double pass configuration. A single, standard echelle grating is used on each side and is illuminated close to true Littrow. Prism cross-dispersers are also used double-pass, and provide a minimum separation between orders of 6 arcsec. Spectral resolution is 19,000 and 25,000 on the red and blue sides, respectively, with a 1 arcsec slit. Typical rms image diameter is less than 0.2 arcsec, so that resolution increases linearly with decreasing slit width. The standard observing mode will use a slit up to 5" long, however a fiber-fed mode will also be available using blocking filters to select the desired orders for up to 256 objects at a time. In this paper, we describe the optical and mechanical design of the instrument.
We present the design for an optical spectrograph for the 6.5-meter Magellan II Telescope. The spectrograph covers the full visible spectrum in a single exposure at very high efficiency through a dual-channel design and the use of volume phase holographic (VPH) gratings in lieu of traditional surface gratings. A pair of symmetric fold mirrors about the grating keep the spectrograph in Littrow configuration, eliminating the need for an articulated camera. Efficient VPH prescriptions have been developed for all resolution modes up to R=11,000. The resulting design is, mechanically and optically, relatively simple, compact, and inexpensive.
The Magellan Project 6.5 Meter Telescope is an alt-azimuth Tripod-Disk design currently under construction. The telescope, which is a joint project of the Carnegie Observatories and the University of Arizona, will be located at the Las Campanas Observatory, Chile. An overview of the structural design, including its evolutionary history, is presented. In addition, two critical mechanical systems which have been prototyped and tested are described. The direct friction drives are used on the telescope main axes and instrument rotators. The vane-end actuator system is used to maintain collimation and focus on any of the four secondary mirror assemblies for which the system is designed.
The present evaluation of the design philosophy of the Apache Point Observatory's 3.5-m altazimuth-fork mount telescope gives attention to such detail-design problems as the mirror-cover system, the upper azimuth bearing and support system, and the spherical bearing mountings. A four-roller constraint for the upper azimuth bearing and support system proved to be a superior design solution than the originally intended two-roller constraint. A cone-shaped structure on the lower fork defines the azimuth axis; the center of the drive disk defines the top end of the axis while the spherical roller thrust bearing defines the lower end.