In preparation for the Dark Energy Spectroscopic Instrument (DESI), a new top end was installed on the Mayall 4-meter telescope at Kitt Peak National Observatory. The refurbished telescope and the DESI instrument were successfully commissioned on sky between 2019 October and 2020 March. Here we describe the pointing, tracking and imaging performance of the Mayall telescope equipped with its new DESI prime focus corrector, as measured by six guider cameras sampling the outer edge of DESI’s focal plane. Analyzing ~500,000 guider images acquired during commissioning, we find a median delivered image FWHM of 1.1 arcseconds (in the r-band at 650 nm), with the distribution extending to a best-case value of ~0.6 arcseconds. The point spread function is well characterized by a Moffat profile with a power-law index of β ≈ 3.5 and little dependence of β on FWHM. The shape and size of the PSF delivered by the new corrector at a field angle of 1.57 degrees are very similar to those measured with the old Mayall corrector on axis. We also find that the Mayall achieves excellent pointing accuracy (several arcseconds RMS) and minimal open-loop tracking drift (< 1 milliarcsecond per second), improvements on the telecope’s pre-DESI performance. In the future, employing DESI’s active focus adjustment capabilities will likely further improve the Mayall/DESI delivered image quality.
The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the extensive preparations of the Mayall telescope and its environs for DESI, and will report on progress-to-date of the installation of DESI itself.
The Mayall 4-meter telescope will soon host the Dark Energy Spectroscopic Instrument (DESI). To integrate DESI into Mayall’s software ecosystem we built an engineering data system called MED (Mayall Engineering Database) that meets the following requirements. (1) MED consists of proven, open-source components to minimize its development and deployment efforts. (2) MED collects data from various sources (log-rotated flat files, existing SQL databases, and our inhouse messaging protocol) to provide a single source for communication between the DESI software and Mayall’s existing subsystems (TCS, dome, primary mirror, weather stations) or future ones (e.g. new calibration lamps). (3) MED facilitates monitoring and troubleshooting by providing an easy way to graph time series in real time or graph time series collected over the past year. (4) MED facilitates generating audio-visual alarms in the control room (e.g. when the dome vignettes) as well as automated email alerts (e.g. when the computer room temperature exceeds 30ºC). (5) MED facilitates semiautomated generation of end-of-night metrics (actual time spent on science, instrument overhead, time lost to technical problems or weather, etc.) that go into a night-log report. (6) MED has persistent, long-term storage for metrics that help with performance analysis and strategic planning. (7) The part of MED essential for science operations at night has builtin capability for high-availability. (8) Finally, for maximum flexibility MED is schema-less. We describe MED’s design and open-source technologies. Our requirements involve 3 timescales, each with its own database: SQL (long) is for metrics that we need to keep forever. InfluxDB (medium) is a time series database that stores variables for one year and, along with Grafana as its visualization front-end, is for monitoring and troubleshooting. Redis (short) is an in-memory data structure store that lacks history, as it keeps the latest value for each variable, and is for system operations, acting as the message broker between subsystems. We outline our Redis data structure and its high-resolution time stamp. We also describe MED’s implementation techniques and show how we tie the open-source components together with scripts and config files, and take advantage of Fluentd, another open-source tool, to convert and pipe telemetry from one source to another with ease
The Dark Energy Spectroscopic Instrument (DESI) is under construction and will be used to measure the expansion history of the Universe using the Baryon Acoustic Oscillation (BAO) technique and the growth of structure using redshift-space distortions (RSD). The spectra of 30 million galaxies over 14000 sq deg will be measured over the course of the experiment. In order to provide spectroscopic targets for the DESI survey, we are carrying out a three-band (g,r,z ) imaging survey of the sky using the NOAO 4-m telescopes at Kitt Peak National Observatory (KPNO) and the Cerro Tololo Interamerican Observatory (CTIO). At KPNO, we will use an upgraded version of the Mayall 4m telescope prime focus camera, Mosaic3, to carry out a z-band survey of the Northern Galactic Cap at declinations δ≥+30 degrees. By equipping an existing Dewar with four 4kx4k fully depleted CCDs manufactured by the Lawrence Berkeley National Laboratory (LBNL), we increased the z-band throughput of the system by a factor of 1.6. These devices have the thickest active area fielded at a telescope. The Mosaic3 z-band survey will be complemented by g-band and r-band observations using the Bok telescope and 90 Prime imager on Kitt Peak. We describe the upgrade and performance of the Mosaic3 instrument and the scope of the northern survey.
Motivated by a desire to improve the KPNO Mayall 4m telescope’s pointing and tracking performance prior to the start of the DESI installation and by a need to improve the maintainability of its telescope control system (TCS), we recently completed a major modernization of that system based heavily on recent changes made at the CTIO Blanco 4m, as described by Warner et al (2012). We describe here the things we did differently from the Blanco upgrade. We also present results from the as-built performance of the new servo and pointing systems.
The Mayall 4-meter telescope recently went through a major modernization of its telescope control system in preparation for DESI. We describe MPK (Mayall Pointing Kernel), our new software for telescope control. MPK outputs a 20Hz position-based trajectory with a velocity component, which feeds into Mayall’s new servo system over a socket. We wrote a simple yet realistic servo simulator that let us develop MPK mostly without access to real hardware, and also lets us provide other teams with a Mayall simulator as test bed for development of new instruments. MPK has a small core comprised of prioritized, soft real-time threads. Access to the core’s services is via MPK’s main thread, a complete, interactive Tcl/Tk shell, which gives us the power and flexibility of a scripting language to add any other features, from GUIs, to modules for interaction with critical subsystems like dome or guider, to an API for networked clients of a new instrument (e.g., DESI). MPK is designed for long term maintainability: it runs on a stock computer and Linux OS, and uses only standard, open source libraries, except for commercial software that comes with source code in ANSI C/C++. We discuss the technical details of how MPK combines the Reflexxes motion library with the TCSpk/TPK pointing library to generically handle any motion requests, from slews to offsets to sidereal or non-sidereal tracking. We show how MPK calculates when the servos have reached a steady state. We also discuss our TPOINT modeling strategy and report performance results.
We report on the implementation of a star tracker camera to improve the telescope pointing and tracking, at the
WIYN 3.5 m telescope on Kitt Peak, Arizona. We base the overall concept on a star tracker system developed
at the University of Wisconsin and routinely in use now for rocket and high-altitude balloon navigation. This
fairly simple system provides pointing and station-keeping information, accurate to a few arcseconds, typically
within a second.
The WIYN Tip-Tilt Module (WTTM) is an addition to the existing Instrument Adapter System (IAS) providing a high performance optical-NIR image stabilized port on the WIYN 3.5m telescope. The WTTM optical system uses a 3-mirror off-axis design along with a high bandwidth tilt mirror. The WTTM is a reimaging system with 15% magnification producing a 4x4 arcminute field of view and near diffraction limited imagery from 400-2000nm. The optics are diamond turned in electroless Nickel over an Aluminum substrate. The WTTM opto-mechanical assembly was designed and built using the principals of the "build-to-print" technique, where the entire system is fabricated and assembled to tolerance with no adjustments. A unique high performance error sensor, using an internal mirrorlette array that feeds 4 fiber coupled avalanche photodiode photon counters, provides the tilt signal. The system runs under the Real-Time Linux operating system providing a maximum closed loop rate of 3khz. In this paper we report on the successful lab testing, verification of the "build-to-print" technique and on telescope performance of the WTTM.