Paul J. Lotz

Status and performance of the Discovery Channel Telescope during commissioning

Lowell Observatorys Discovery Channel Telescope is a 4.3m telescope designed for optical and near infrared astronomical observation. At first light, the telescope will have a cube capable of carrying five instruments and the wave front sensing and guider system at the f/6.1 RC focus. The corrected RC focus field of view is 30’ in diameter. Nasmyth and prime focus can be instrumented subsequently. Early commissioning work with the installed primary mirror and its support system started out using one of the wave front sensing probes mounted at prime focus, and has continued at RC with the recent installation of the secondary mirror. We will report on the on-sky pointing and tracking performance of the telescope, initial assessment of the functionality of the active optics support system, and tests of the early image quality of the telescope and optics. We will also describe the suite of first light instruments, and early science operations.

LSST Telescope and site status

The Large Synoptic Survey Telescope (LSST) has recently completed its Final Design Review and the Project is preparing for a 2014 construction authorization. The telescope system design supports the LSST mission to conduct a wide, fast, deep survey via a 3-mirror wide field of view optical design, a 3.2-Gpixel camera, and an automated data processing system. The observatory will be constructed in Chile on the summit of Cerro Pachón. This paper summarizes the status of the Telescope and Site group. This group is tasked with design, analysis, and construction of the summit and base facilities and infrastructure necessary to control the survey, capture the light, and calibrate the data. Several early procurements of major telescope subsystems have been completed and awarded to vendors, including the mirror systems, telescope mount assembly, hexapod and rotator systems, and the summit facility. These early contracts provide for the final design of interfaces based upon vendor specific approaches and will enable swift transition into construction. The status of these subsystems and future LSST plans during construction are presented.

The active optics system for the Discovery Channel Telescope

The Discovery Channel Telescope (DCT) is a 4.3-meter telescope designed for dual optical configurations, featuring an f/6.1 Ritchey-Chretien prescription with a 0.5° field-of-view, and a corrected f/2.3 prime focus with a 2° field-of-view. The DCT Active Optics System (AOS) maintains collimation and mirror figure to provide seeing limited images across the focal planes and rapid settling times to minimize observing overhead, using a combination of feed-forward and lowbandwidth feedback control via wavefront sensing. Collimation is maintained by tip-tilt-piston control of the M2 assembly and articulating M1 within its cell, taking advantage of the 120 degree-of-freedom support used for figure control. We present an overview of the AOS design and principles of operation, and a summary of progress and results to date.

LSST control software component design

Construction of the Large Synoptic Survey Telescope system involves several different organizations, a situation that poses many challenges at the time of the software integration of the components. To ensure commonality for the purposes of usability, maintainability, and robustness, the LSST software teams have agreed to the following for system software components: a summary state machine, a manner of managing settings, a flexible solution to specify controller/controllee relationships reliably as needed, and a paradigm for responding to and communicating alarms. This paper describes these agreed solutions and the factors that motivated these.

Discovery Channel Telescope software key technologies

The Discovery Channel Telescope (DCT) is a 4.3-meter astronomical research telescope being built in northern Arizona as a partnership between Discovery Communications and Lowell Observatory. The project software team has designed and partially implemented a component-based system. We describe here the key features of that design (state-based components that respond to signals) and detail specific implementation technologies we expect to be of most interest: examples of the Command Pattern, State Pattern, and XML-based configuration file handling using LabVIEW classes and shared variables with logging and alarming features.

Discovery Channel Telescope software development overview

The Discovery Channel Telescope (DCT) is a 4.3-meter astronomical research telescope being built in northern Arizona as a partnership between Discovery Communications and Lowell Observatory. We present an overview of the current status of the project software effort, including the iterative development process (including planning, requirements management and traceability, design, code, test, issue tracking, and version control), our experience with management and design techniques and tools the team uses that support the effort, key features of the component-based architectural design, and implementation examples that leverage new LabVIEW-based technologies.

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.

Final design of the LSST hexapods and rotator

The Large Synoptic Survey Telescope (LSST) is a large (8.4 meter) wide-field (3.5 degree) survey telescope, which will be located on the Cerro Pachón summit in Chile. Both the Secondary Mirror (M2) Cell Assembly and Camera utilize hexapods to facilitate optical positioning relative to the Primary/Tertiary (M1M3) Mirror. A rotator resides between the Camera and its hexapod to facilitate tracking. The final design of the hexapods and rotator has been completed by Moog CSA, who are also providing the fabrication and integration and testing. Geometric considerations preclude the use of a conventional hexapod arrangement for the M2 Hexapod. To produce a more structurally efficient configuration the camera hexapod and camera rotator will be produced as a single unit. The requirements of the M2 Hexapod and Camera Hexapod are very similar; consequently to facilitate maintainability both hexapods will utilize identical actuators. The open loop operation of the optical system imposes strict requirements on allowable hysteresis. This requires that the hexapod actuators use flexures rather than more traditional end joints. Operation of the LSST requires high natural frequencies, consequently, to reduce the mass relative to the stiffness, a unique THK rail and carriage system is utilized rather than the more traditional slew bearing. This system utilizes two concentric tracks and 18 carriages.

Discovery Channel Telescope software component template and state design: principles and implementation

The Discovery Channel Telescope is a 4.3m astronomical research telescope in northern Arizona constructed through a partnership between Discovery Communications and Lowell Observatory. The control software for the telescope and observatory systems consists of stand-alone, state-based components that respond to triggers (external signals or internal data changes). Component applications execute on Windows, real-time, and FPGA targets. The team has developed a template for a system component, the implementation of which has yielded large gains in productivity, robustness, and maintainability. These benefits follow from the dependence of the template on common, well-tested code, allowing a developer to focus on application-specific particulars unencumbered by details of infrastructure elements such as communication, and from the separation of concerns the architecture provides, ensuring that modifications are straightforward, separable, and consequently relatively safe. We describe a repeatable design process for developing a state machine design, and show how this translates directly into a concrete implementation utilizing several design patterns, illustrating this with examples from components of the functioning active optics system. We also present a refined top-level state machine design and rules for highly independent component interactions within and between hierarchies that we propose offer a general solution for large component-based control systems.

LSST communications middleware implementation

The LSST communications middleware is based on a set of software abstractions; which provide standard interfaces for common communications services. The observatory requires communication between diverse subsystems, implemented by different contractors, and comprehensive archiving of subsystem status data. The Service Abstraction Layer (SAL) is implemented using open source packages that implement open standards of DDS (Data Distribution Service1) for data communication, and SQL (Standard Query Language) for database access. For every subsystem, abstractions for each of the Telemetry datastreams, along with Command/Response and Events, have been agreed with the appropriate component vendor (such as Dome, TMA, Hexapod), and captured in ICDs (Interface Control Documents).The OpenSplice (Prismtech) Community Edition of DDS provides an LGPL licensed distribution which may be freely redistributed. The availability of the full source code provides assurances that the project will be able to maintain it over the full 10 year survey, independent of the fortunes of the original providers.