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.
This paper provides an overview of the tool, language, and methodology used for Verification and Validation Planning
on the Large Synoptic Survey Telescope (LSST) Project. LSST has implemented a Model Based Systems Engineering
(MBSE) approach as a means of defining all systems engineering planning and definition activities that have historically
been captured in paper documents. Specifically, LSST has adopted the Systems Modeling Language (SysML) standard
and is utilizing a software tool called Enterprise Architect, developed by Sparx Systems. Much of the historical use of
SysML has focused on the early phases of the project life cycle. Our approach is to extend the advantages of MBSE into
later stages of the construction project. This paper details the methodology employed to use the tool to document the
verification planning phases, including the extension of the language to accommodate the project’s needs. The process
includes defining the Verification Plan for each requirement, which in turn consists of a Verification Requirement,
Success Criteria, Verification Method(s), Verification Level, and Verification Owner. Each Verification Method for
each Requirement is defined as a Verification Activity and mapped into Verification Events, which are collections of
activities that can be executed concurrently in an efficient and complementary way. Verification Event dependency and
sequences are modeled using Activity Diagrams. The methodology employed also ties in to the Project Management
Control System (PMCS), which utilizes Primavera P6 software, mapping each Verification Activity as a step in a
planned activity. This approach leads to full traceability from initial Requirement to scheduled, costed, and resource
loaded PMCS task-based activities, ensuring all requirements will be verified.