Michael Warner

ISPI: a wide-field NIR imager for the CTIO Blanco 4-m telescope

The Infrared Side Port Imager ISPI is a facility infrared imager for the CTIO Blanco 4-meter telescope. ISPI has the following capabilities: 1-2.4 micron imaging with an 2K x 2K HgCdTe array, 0.3 arcsec/pixel sampling matched to typical f/8 IR image quality of ~0.6 arcsec and a 10.5 x 10.5 arcmin field of view. First light with ISPI was obtained on September 24 2002, and since January 2003 ISPI has been in operation as a common user instrument. In this paper we discuss operational aspects of ISPI, the behavior of the array and we report on the performance of ISPI during the first one and half year of operation.

MONSOON Image Acquisition System

The MONSOON Image Acquisition System is a scalable, multichannel, high-speed data acquisition system designed for the next-generation optical/infrared detectors and mosaic projects currently under development at NOAO. MONSOON is more than a controller; rather it is new image acquisition architecture, providing a total solution to “detector-limited” image acquisition for all astronomical detectors, scientific and technical, OUV to IR. MONSOON addresses detector-interface as well as the significant data flow and processing issues large-scale imaging systems require. The Monsoon effort is a full-disclosure “open-source” development effort by NOAO in collaboration with the CARA ASTEROID project for the benefit of the astronomical community.

Adaptive periodic error correction for Heidenhain tape encoders

Heidenhain position tape encoders are in use on almost all modern telescopes with excellent results. Performance of these systems can be limited by minor mechanical misalignments between the tape and read head causing errors at the grating period. The first and second harmonics of the measured signal are the dominant errors, and have a varying frequency dependant on axis rate. When the error spectrum is within the mount servo bandwidth it results in periodic telescope pointing jitter. This paper will describe an adaptive error correction using elliptic interpolation of the raw signals, based on the well known compensation technique developed by Heydemann [1]. The approach allows the compensation to track in real time with no need of a large static look-up table, or frequent calibrations. This paper also presents the results obtained after applying this approach on data measured on the SOAR telescope.

Substrate temperature and strain during sputter deposition of aluminum on cast borosilicate glass in a Gemini Observatory coating chamber

Temperature and strain measurements obtained during coating of spin-cast borosilicate samples are presented here with an analysis of these results. These tests were performed for the Large Synoptic Survey Telescope (LSST) project to verify the possible use of sputtering deposition of optical coating on its large 8.4m diameter primary-tertiary mirror. Made of spin-cast borosilicate glass, the working stress of the mirrors nonpolished surfaces is 100 psi (0.69 MPa), resulting in a local temperature difference limit of 5 degrees C. To ensure representative environmental conditions, the tests were performed in the Gemini Observatory coating chamber located in Hawaii, whose design was utilized to develop the LSST coating chamber design. In particular, this coating chamber is equipped with linear magnetrons built with cooled heat shields directly facing the mirror surface. These measurements have demonstrated that it will be safe for the LSST to use a magnetron sputtering process for coating its borosilicate primary-tertiary mirror.

Wind Induced Image Degradation (Jitter) of the LSST Telescope

A wind pressures PSD measured on the Gemini South Telescope was applied to the FEA model of the LSST telescope to determine the RMS motions of the principal optical systems. These motions were then converted to the time domain. The time domain motions were analyzed in the ZEMAX® software to determine the wind induced image degradation. This degradation was shown to be tolerable.

Active Tangent Link System for Transverse Support of Large Thin Meniscus Mirrors

An active tangent link system was developed to provide transverse support for large thin meniscus mirrors. The support system uses six tangent links to control position and distribute compensating force to the mirror. Each of the six tangent links utilizes an electromechanical actuator and an imbedded lever system working through a load cell and flexure. The lever system reduces the stiffness, strength and force resolution requirements of the electromechanical actuator and allows more compact packaging. Although all six actuators are essentially identical, three of them are operated quasi statically, and are only used to position the optic. The other three are actively operated to produce an optimal and repeatable distribution of the transverse load. This repeatable load distribution allows for a more effective application of a look up table and reduces the demands on the active optics system. A control system was developed to manage the quasi static force equilibrium servo loop using a control matrix that computes the displacements needed to correct any force imbalance with good convergence and stability. This system was successfully retrofitted to the 4.3 meter diameter, 100 mm thick SOAR primary mirror to allow for more expeditious convergence of the mirror figure control system. This system is also intended for use as the transverse support system for the LSST 3.4 meter diameter thin meniscus secondary mirror.

ISPI: the infared side port imager for the CITO 4-m telescope

The new operations model for the CTIO Blanco 4-m telescope will use a small suite of fixed facility instruments for imaging and spectroscopy. The Infrared Side Port Imager, ISPI, provides the infrared imaging capability. We describe the optical, mechanical, electronic, and software components of the instrument. The optical design is a refractive camera-collimator system. The cryo-mechanical packaging integrates two LN2-cooled dewars into a compact, straightline unit to fit within space constraints at the bent Cassegrain telescope focus. A HAWAII 2 2048 x 2048 HgCdTe array is operated by an SDSU II array controller. Instrument control is implemented with ArcVIEW, a proprietary LabVIEW-based software package. First light on the telescope is planned for September 2002.

MONSOON: Image Acquisition System or Pixel Server

The MONSOON Image Acquisition System has been designed to meet the need for scalable, multichannel, high-speed image acquisition required for the next-generation optical and infared detectors and mosaic projects currently under development at NOAO as described in other papers at this proceeding such as ORION, NEWFIRM, QUOTA, ODI and LSST. These new systems with their large scale (64 to 2000 channels) and high performance (up to 1Gbyte/s) raise new challenges in terms of communication bandwidth, data storage and data processing requirements which are not adequately met by existing astronomical controllers. In order to meet this demand, new techniques for not only a new detector controller, but rather a new image acquisition architecture, have been defined. These extremely large scale imaging systems also raise less obvious concerns in previously neglected areas of controller design such as physical size and form factor issues, power dissipation and cooling near the telescope, system assembly/test/ integration time, reliability, and total cost of ownership. At NOAO we have taken efforts to look outside of the astronomical community for solutions found in other disciplines to similar classes of problems. A large number of the challenges raised by these system needs are already successfully being faced in other areas such as telecommunications, instrumentation and aerospace. Efforts have also been made to use true commercial off the shelf (COTS) system elements, and find truly technology independent solutions for a number of system design issues whenever possible. The Monsoon effort is a full-disclosure development effort by NOAO in collaboration with the CARA ASTEROID project for the benefit of the astronomical community.

Large Synoptic Survey Telescope mount final design

This paper describes the status and details of the large synoptic survey telescope1,2,3 mount assembly (TMA). On June 9th, 2014 the contract for the design and build of the large synoptic survey telescope mount assembly (TMA) was awarded to GHESA Ingeniería y Tecnología, S.A. and Asturfeito, S.A. The design successfully passed the preliminary design review on October 2, 2015 and the final design review January 29, 2016. This paper describes the detailed design by subsystem, analytical model results, preparations being taken to complete the fabrication, and the transportation and installation plans to install the mount on Cerro Pachón in Chile. This large project is the culmination of work by many people and the authors would like to thank everyone that has contributed to the success of this project.

Dark Energy Camera installation at CTIO: technical challenges

The Dark Energy Camera (DECam) is a new prime focus, wide-field imager for the V. M. Blanco 4-m telescope at CTIO. Instrumentation includes large, five-lens optical corrector mounted on hexapod mechanism for fine adjustment, filters, and a 519 Megapixel camera vessel; all integrated in a cage similar to the existing telescope prime focus structure. Currently Blanco allows a flip of this structure such that the f/8 secondary mirror, mounted on the back of the cage, points towards the primary mirror for Ritchey-Chretien observations. DECam will maintain this capability by attaching the existing F/8 mirror cell to the front of the new cage. Installation of this 8,600 kg instrument required the removal from the telescope of the primary mirror, the removal of the old prime focus assembly, and fine adjustment of large, over-constrained mechanisms followed by reassembly. A large facility shutdown was scheduled for this upgrade and several tools, fixtures, monitoring systems and procedures were developed in order to identify and then recover the optical alignment of the system, to control the distribution of stresses during tuning of the installation and to maintain the balance of the telescope with significant added mass. The final goal has been to maintain high performance of the telescope for both the existing f/8 Ritchey-Chretien focus mounted instruments and the new DECam instrument now in commissioning. The challenges presented in handling large elements, real-time monitoring, alignment, verification and feedback are described.