Michel D. Ingham

Engineering Complex Embedded Systems with State Analysis and the Mission Data System

It has become clear that spacecraft system complexity is reaching a threshold where customary methods of control are no longer affordable or sufficiently reliable. At the heart of this problem are the conventional approaches to systems and software engineering based on subsystem-level functional decomposition, which fail to scale in the tangled web of interactions typically encountered in complex spacecraft designs. Furthermore, there is a fundamental gap between the requirements on software specified by systems engineers and the implementation of these requirements by software engineers. Software engineers must perform the translation of requirements into software code, hoping to accurately capture the systems engineers understanding of the system behavior, which is not always explicitly specified. This gap opens up the possibility for misinterpretation of the systems engineer s intent, potentially leading to software errors. This problem is addressed by a systems engineering methodology called State Analysis, which provides a process for capturing system and software requirements in the form of explicit models. This paper describes how requirements for complex aerospace systems can be developed using State Analysis and how these requirements inform the design of the system software, using representative spacecraft examples.

An ontology for State Analysis: Formalizing the mapping to SysML

State Analysis is a methodology developed over the last decade for architecting, designing and documenting complex control systems. Although it was originally conceived for designing robotic spacecraft, recent applications include the design of control systems for large ground-based telescopes. The European Southern Observatory (ESO) began a project to design the European Extremely Large Telescope (E-ELT), which will require coordinated control of over a thousand articulated mirror segments. The designers are using State Analysis as a methodology and the Systems Modeling Language (SysML) as a modeling and documentation language in this task. To effectively apply the State Analysis methodology in this context it became necessary to provide ontological definitions of the concepts and relations in State Analysis and greater flexibility through a mapping of State Analysis into a practical extension of SysML. The ontology provides the formal basis for verifying compliance with State Analysis semantics including architectural constraints. The SysML extension provides the practical basis for applying the State Analysis methodology with SysML tools. This paper will discuss the method used to develop these formalisms (the ontology), the formalisms themselves, the mapping to SysML and approach to using these formalisms to specify a control system and enforce architectural constraints in a SysML model.

Ontology and modeling patterns for state-based behavior representation

This paper provides an approach to capture state-based behavior of elements, that is, the specification of their state evolution in time, and the interactions amongst them. Elements can be components (e.g., sensors, actuators) or environments, and are characterized by state variables that vary with time. The behaviors of these elements, as well as interactions among them are represented through constraints on state variables. This paper discusses the concepts and relationships introduced in this behavior ontology, and the modeling patterns associated with it. Two example cases are provided to illustrate their usage, as well as to demonstrate the flexibility and scalability of the behavior ontology: a simple flashlight electrical model and a more complex spacecraft model involving instruments, power and data behaviors. Finally, an implementation in a SysML profile is provided.

Application of state analysis and goal-based operations to a MER mission scenario

†‡ § ** State Ana lysis is a model -based systems engineering methodology employing a rigorous discovery process which articulates operations concepts and operability needs as an integrated part of system design. The process produces requirements on system and software desi gn in the form of explicit models which describe the system behavior in terms of state variables and the re lationships among them 1 . By applying State Analysis to an actual MER flight mission scenario, this study addresses the specific real world challenge s of complex space operations and explores technologies that can be brought to bear on future missions. The paper first describes the tools currently used on a daily basis for MER operations planning and provides an in -depth description of the planning pr ocess, in the context of a Martian day’s worth of rover engineering activities, resource modeling, flight rules, science observations, and more. It then describes how State Analysis allows for the specification of a corresponding goal -based sequence that accomplishes the same objectives, with several important additional bene fits.

Achieving control and interoperability through unified model-based systems and software engineering

*† ‡ Control and interoperation of complex systems is one of the most difficult challenges facing NASA’s Exploration Systems Mission Directorate. An integrated but diverse array of vehicles, habitats, and supporting facilities, evolving over the long course of the enterprise, must perform ever more complex tasks while moving steadily away from the sphere of ground support and intervention. Interoperability needs will grow to unprecedented levels as systems become more dependent on one another than on support from home. Accomplishing this with consistent safety and reliability calls for a long-term strategy. This paper describes the control challenge faced by future exploration systems and outlines a realistic approach to solving it, based upon a unified, principled architectural approach to both software and systems engineering. It concludes by suggesting the steps necessary to put this capability in place for exploration systems.

Prototyping a Domain-Specific Language for Monitor and Control Systems

This paper describes a domain-specific language prototype developed for the NASA Constellationlaunchcontrolsystemproject.Akeyelementofthelaunchcontrolsystemarchitecture,thedomain-specificlanguageprototypeisaspecializedmonitorandcontrollanguage composed of constructs for specifying and programming test, checkout, and launch processing applications for flight and ground systems. The principal objectives of the prototyping activity were to perform a proof-of-concept of an approach to ultimately lower the lifecycle costs of application software for the launch control system, and to explore mitigations for a number of development risks perceived by the project. The language has been implemented as a library that extends the dynamically-typed Python scripting language, and validated in a demonstration of capability required for Constellation.A study of the statically typed Scala programminglanguageasanalternativedomain-specificlanguageimplementationlanguage is also presented.

A Control Architecture for Safe Human-Robotic Interactions During Lunar Surface Operations

** †† ‡‡ Long duration human-robotic missions to the Moon and beyond will require increased use of automation beyond current Space Shuttle and International Space Station practice. This paper explores the application of a model- and state-based goal-oriented control architecture to solving the problem of coordinating activities between humans and robots to improve the reliability and safety of these interactions. A goal-oriented control system continuously enforces constraints on states of the system to achieve not only control goals, but also to enforce passive constraints, such as safety constraints, on those activities.