The Integration and Verification Testing of the Large Synoptic Survey Telescope (LSST) Camera is described. The LSST Camera will be the largest astronomical camera ever constructed, featuring a 3.2 giga-pixel focal plane mosaic of 189 CCDs with in-vacuum controllers and readout, dedicated guider and wavefront CCDs, a three element corrector with a 1.6-meter diameter initial optic, six optical filters covering wavelengths from 320 to 1000 nm with a novel filter exchange mechanism, and camera-control and data acquisition capable of digitizing each image in two seconds. In this paper, we describe the integration processes under way to assemble the Camera and the associated verification testing program. The Camera assembly proceeds along two parallel paths: one for the focal plane and cryostat and the other for the Camera structure itself. A range of verification tests will be performed interspersed with assembly to verify design requirements with a test-as-you-build methodology. Ultimately, the cryostat will be installed into the Camera structure as the two assembly paths merge, and a suite of final Camera system tests performed. The LSST Camera is scheduled for completion and delivery to the LSST observatory in 2020.
The Large Synoptic Survey Telescope, under construction in Chile, is an 8.4 m optical survey telescope with a dedicated 3.2 Giga-pixel camera. The design and construction of the camera is spearheaded at SLAC National Accelerator Laboratory and here we present a general overview of the camera integration and test activities. An overview of the methodologies used for the planning and management of this subsystem will be given, along with a high-level summary of the status of the major pieces of I&T hardware. Finally a brief update will be given on the current state of the LSST Camera integration and testing program.
The LSST Camera focal plane comprises twenty-one raft tower modules (RTMs), each with nine CCD sensors and their associated electronics. RTMs are assembled at Brookhaven National Lab and shipped to SLAC National Lab, where they must be re-verified before being assembled into the full focal plane. The process for accepting an RTM at SLAC has been thoroughly documented, including unpacking a raft from its shipping container, verifying aliveness of the electrical connections, performing metrology and electro-optical testing in an environment similar to the full Camera, and finally storing the RTM until it can be installed into the LSST Camera
We† provide an overview of the Model Based Systems Engineering (MBSE) language, tool, and methodology being used in our development of the Operational Plan for Large Synoptic Survey Telescope (LSST) operations. LSST’s Systems Engineering (SE) team is using a model-based approach to operational plan development to: 1) capture the topdown stakeholders’ needs and functional allocations defining the scope, required tasks, and personnel needed for operations, and 2) capture the bottom-up operations and maintenance activities required to conduct the LSST survey across its distributed operations sites for the full ten year survey duration. To accomplish these complimentary goals and ensure that they result in self-consistent results, we have developed a holistic approach using the Sparx Enterprise Architect modeling tool and Systems Modeling Language (SysML). This approach utilizes SysML Use Cases, Actors, associated relationships, and Activity Diagrams to document and refine all of the major operations and maintenance activities that will be required to successfully operate the observatory and meet stakeholder expectations. We have developed several customized extensions of the SysML language including the creation of a custom stereotyped Use Case element with unique tagged values, as well as unique association connectors and Actor stereotypes. We demonstrate this customized MBSE methodology enables us to define: 1) the rolls each human Actor must take on to successfully carry out the activities associated with the Use Cases; 2) the skills each Actor must possess; 3) the functional allocation of all required stakeholder activities and Use Cases to organizational entities tasked with carrying them out; and 4) the organization structure required to successfully execute the operational survey. Our approach allows for continual refinement utilizing the systems engineering spiral method to expose finer levels of detail as necessary. For example, the bottom-up, Use Case-driven approach will be deployed in the future to develop the detailed work procedures required to successfully execute each operational activity.
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.
The Large Synoptic Survey Telescope project was an early adopter of SysML and Model Based Systems Engineering
practices. The LSST project began using MBSE for requirements engineering beginning in 2006 shortly after the initial
release of the first SysML standard. Out of this early work the LSST’s MBSE effort has grown to include system
requirements, operational use cases, physical system definition, interfaces, and system states along with behavior
sequences and activities. In this paper we describe our approach and methodology for cross-linking these system
elements over the three classical systems engineering domains – requirement, functional and physical - into the LSST
System Architecture model. We also show how this model is used as the central element to the overall project systems
engineering effort. More recently we have begun to use the cross-linked modeled system architecture to develop and
plan the system verification and test process. In presenting this work we also describe “lessons learned” from several
missteps the project has had with MBSE. Lastly, we conclude by summarizing the overall status of the LSST’s System
Architecture model and our plans for the future as the LSST heads toward construction.
The Large Synoptic Survey Telescope is a complex hardware - software system of systems, making up a highly
automated observatory in the form of an 8.4m wide-field telescope, a 3.2 billion pixel camera, and a peta-scale data
processing and archiving system. As a project, the LSST is using model based systems engineering (MBSE)
methodology for developing the overall system architecture coded with the Systems Modeling Language (SysML).
With SysML we use a recursive process to establish three-fold relationships between requirements, logical & physical
structural component definitions, and overall behavior (activities and sequences) at successively deeper levels of
abstraction and detail. Using this process we have analyzed and refined the LSST system design, ensuring the
consistency and completeness of the full set of requirements and their match to associated system structure and
behavior. As the recursion process proceeds to deeper levels we derive more detailed requirements and specifications,
and ensure their traceability. We also expose, define, and specify critical system interfaces, physical and information
flows, and clarify the logic and control flows governing system behavior. The resulting integrated model database is
used to generate documentation and specifications and will evolve to support activities from construction through final
integration, test, and commissioning, serving as a living representation of the LSST as designed and built. We discuss
the methodology and present several examples of its application to specific systems engineering challenges in the LSST
In this paper we describe the data acquisition and control system of the Dark Energy Camera (DECam),
which will be the primary instrument used in the Dark Energy Survey (DES). DES is a high precision multibandpath
wide area survey of 5000 square degrees of the southern sky. DECam currently under construction
at Fermilab will be a 3 square degree mosaic camera mounted at the prime focus of the Blanco 4m telescope
at the Cerro-Tololo International Observatory (CTIO). The DECam data acquisition system (SISPI) is
implemented as a distributed multi-processor system with a software architecture built on the Client-Server
and Publish-Subscribe design patterns. The underlying message passing protocol is based on PYRO, a
powerful distributed object technology system written entirely in Python. A distributed shared variable
system was added to support exchange of telemetry data and other information between different components
of the system. In this paper we discuss the SISPI infrastructure software, the image pipeline, the observer
interface and quality monitoring system, and the instrument control system.
The Dark Energy Survey (DES) is a 5000 square degree survey of the southern galactic cap set to take place
on the Blanco 4-m telescope at Cerra Tololo Inter-American Observatory. A new 500 MP camera and control
system are being developed for this survey. To facilitate the data acquisition and control, a new user interface
is being designed that utilizes the massive improvements in web based technologies in the past year. The work
being done on DES shows that these new technologies provide the functionality and performance required to
provide a productive and enjoyable user experience in the browser.
The Dark Energy Survey Collaboration is building the Dark Energy Camera (DECam), a 3 square degree, 520
Megapixel CCD camera which will be mounted on the Blanco 4-meter telescope at CTIO. DECam will be used to
perform the 5000 sq. deg. Dark Energy Survey with 30% of the telescope time over a 5 year period. During the
remainder of the time, and after the survey, DECam will be available as a community instrument. Construction of
DECam is well underway. Integration and testing of the major system components has already begun at Fermilab and
the collaborating institutions.
The LSST Camera Control System (CCS) will manage the activities of the various camera subsystems and coordinate
those activities with the LSST Observatory Control System (OCS). The CCS comprises a set of modules (nominally
implemented in software) which are each responsible for managing one camera subsystem. Generally, a control module
will be a long lived "server" process running on an embedded computer in the subsystem. Multiple control modules may
run on a single computer or a module may be implemented in "firmware" on a subsystem. In any case control modules
must exchange messages and status data with a master control module (MCM). The main features of this approach are:
(1) control is distributed to the local subsystem level; (2) the systems follow a "Master/Slave" strategy; (3) coordination
will be achieved by the exchange of messages through the interfaces between the CCS and its subsystems. The interface
between the camera data acquisition system and its downstream clients is also presented.
The MACHO experiment is searching for dark matter in the halo of the Galaxy by monitoring more than 50 million stars in the LMC, SMC, and Galactic bulge for gravitational microlensing events. The hardware consists of a 50 inch telescope, a two-color 32 megapixel ccd camera and a network of computers. On clear nights the system generates up to 8 GB of raw data and 1 GB of reduced data. The computer system is responsible for all realtime control tasks, for data reduction, and for storing all data associated with each observation in a database. The subject of this paper is the software system that handles these functions. It is an integrated system controlled by Petri nets that consists of multiple processes communicating via mailboxes and a bulletin board. The system is highly automated, readily extensive, and incorporates flexible error recovery capabilities. It is implemented with C++ in a Unix environment.
We have developed an astronomical imaging system that incorporates a total of eight 2048 X 2048 pixel CCDs into two focal planes, to allow simultaneous imaging in two colors. Each focal plane comprises four 'edge-buttable' detector arrays, on custom Kovar mounts. The clocking and bias voltage levels for each CCD are independently adjustable, but all the CCDs are operated synchronously. The sixteen analog outputs (two per chip) are measured at 16 bits with commercially available correlated double sampling A/D converters. The resulting 74 MBytes of data per frame are transferred over fiber optic links into dual-ported VME memory. The total readout time is just over one minute. We obtain read noise ranging from 6.5 e<SUP>-</SUP> to 10 e<SUP>-</SUP> for the various channels when digitizing at 34 Kpixels/sec, with full well depths (MPP mode) of approximately 100,000 e<SUP>-</SUP> per 15 micrometers X 15 micrometers pixel. This instrument is currently being used in a search of gravitational microlensing from compact objects in our Galactic halo, using the newly refurbished 1.3 m telescope at the Mt. Stromlo Observatory, Australia.