The Apache Point Observatory Galactic Evolution Experiment (APOGEE) uses a dedicated 300-fiber, narrow-band
near-infrared (1.51-1.7 μm), high resolution (R~22,500) spectrograph to survey approximately 100,000 giant stars across
the Milky Way. This three-year survey, in operation since late-summer 2011 as part of the Sloan Digital Sky Survey III
(SDSS III), will revolutionize our understanding of the kinematical and chemical enrichment histories of all Galactic
stellar populations. We present the performance of the instrument from its first year in operation. The instrument is
housed in a separate building adjacent to the 2.5-m SDSS telescope and fed light via approximately 45-meter fiber runs
from the telescope. The instrument design includes numerous innovations including a gang connector that allows
simultaneous connection of all fibers with a single plug to a telescope cartridge that positions the fibers on the sky,
numerous places in the fiber train in which focal ratio degradation had to be minimized, a large mosaic-VPH (290 mm x
475 mm elliptically-shaped recorded area), an f/1.4 six-element refractive camera featuring silicon and fused silica
elements with diameters as large as 393 mm, three near-infrared detectors mounted in a 1 x 3 mosaic with sub-pixel
translation capability, and all of these components housed within a custom, LN2-cooled, stainless steel vacuum cryostat
with dimensions 1.4-m x 2.3-m x 1.3-m.
Astronomy is changing. Large projects, large collaborations, and large budgets are becoming the norm. The
Sloan Digital Sky Survey (SDSS) is one example of this new astronomy, and in operating the original survey, we
put in place and learned many valuable operating principles. Scientists sometimes have the tendency to invent
everything themselves but when budgets are large, deadlines are many, and both are tight, learning from others
and applying it appropriately can make the difference between success and failure. We offer here our experiences
well as our thoughts, opinions, and beliefs on what we learned in operating the SDSS.
The Sloan Digital Sky Survey is the largest redshift survey conducted to date, and the principal survey observations have all been conducted on the dedicated SDSS 2.5m and 0.5m telescopes at Apache Point Observatory. While the whole survey has many unique features, this article concentrates on a description of the systems surrounding the dual fibre-input spectrographs that obtain all the survey spectra and that are capable of recording 5,760 individual spectra per night on an industrial, consistent, mass-production basis. It is hoped that the successes and lessons learned will prove instructive for future large spectrographic surveys.
The SDSS telescope is housed, when not in use, in a roll-off enclosure. This enclosure rolls away from the telescope a distance of 60 feet, leaving the telescope fully exposed for operations.
Design considerations for wind and solar loading, thermal venting, conditioning and stability are reviewed. Originally, the enclosure had been constructed to minimize its surface area obstruction to the telescopes field of view. This design feature, however, offered little room to perform engineering tasks during non-operational time. An upgrade to the structure, in the form of raising the roof, was instituted. This improvement greatly enhanced the engineering and testing functions performed on the telescope, thereby increasing operational efficiency and the time allotted to engineering tasks.
Problems maintaining and associated with weather sealing, lightning protection, truck wheel alignment, altitude effects on truck controllers and thermal conditioning are examined. Communication and electrical connections between stationary and moving elements of the enclosure are described. Two types of systems, to date, have been used - one a reel and the other a slider system. Advantages and disadvantages of both are examined from the perspective of four years experience.
This paper will describe the concerns, parameters and restrictions in the design and construction of the instrument rotator used on the SDSS telescope.
The rotator provides support for two 600 Lb. Spectrographs, through all axes motion, without causing harmful radial moments to be translated to its inner ring which supports the mosaic imaging camera. This is accomplished using an outer-inner ring design. The outer ring is a thin-walled box structure incorporating the drive surface and is attached to the inner ring through a steel membrane. This rotator design requires the telescope’s primary support structure to provide final structural integrity. Due to this feature, a special fixture was needed to transport the rotator from the vendor and to install it onto the telescope.
Positional accuracy and feedback is provided by an optical tape and read-head system manufactured by Heidenhain and attached to the inner ring. The drive motor was designed to use the same motor as those employed for the other two telescope axes, thus minimizing the spare-parts inventory and maintenance. Its drive pinion is of a pinch design, with the pinion axis parallel to rotator radius. A great deal of attention and planning was required in the construction of the box frame outer ring and the induction heat-treating of the drive surface.
Drive surface tolerances were maintained within +/-0.001 inches, and internal stress cracks from heat-treating were minimal.
The Telescope Performance Monitor (TPM) installed at the Sloan Digital Sky Survey (SDSS) located at Apache Point Observatory provides access to real-time and archived engineering data. The modularity present in the underlying Experimental Physics and Industrial Control System (EPICS) toolkit allows the observers and operations staff to develop their own approaches to data access and analysis. These techniques are summarized and the use of the TPM to solve critical project issues including analysis and correction of thermal management problems are presented.
This paper describes how the Sloan Digital Sky Survey telescopes are operated. A brief introduction to the survey science goals, hardware, and software systems is provided. Operational issues are discussed such as staffing, observing planning, real-time quality assurance, and data handling, with an emphasis on how we maximize operational efficiency.
Optimizing the performance of a telescope requires the ability to accurately measure and monitor the spatial variation of temperature in critical components. Surfaces near a telescope may warm or chill ambient air and cause image degradation. It is desirable to monitor the temperature of such systems. The design, fabrication and testing of a reliable, low-cost, multiplexed temperature measurement system with a resolution and stability approaching 0.01 degree(s)C is described. This system, with 176 temperature sensors, will be used to monitor the performance of a 3.5 m borosilicate mirror ventilation system. It is applicable to a broad range of telescope and telescope enclosure temperature measurement problems.