Abstract-Traditional requirements specification and hazard analysis techniques have not kept pace with the increasing complexity and constraints of modern space systems development. These techniques are incomplete and often consider safety late in the development cycle when the most significant design decisions have already been made. The lack of an integrated approach to perform safety-driven system development from the beginning of the system lifecycle hinders the ability to create safe space systems on time and within budget. To address this need, the authors have created an integrated methodology for safety-driven system development that combines four state-of-the-art techniques: 1) Intent Specification, a framework for organizing system development and operational information in a hierarchical structure; 2) the STAMP model of accident causation, a system-theoretic framework upon which to base more powerful safety engineering techniques; 3) STAMPbased Hazard Analysis (STPA); and 4) State Analysis, a model-based systems engineering approach. The iterative approach specified in the methodology employs State Analysis in the modeling of system behavior. STPA is used to identify system hazards and the constraints that must be enforced to mitigate these hazards.Finally, Intent Specification is used to document traceability of behavioral requirements and subject them to formal analysis using the SpecTRM-RL software package. In this paper, 1,2 the application of this methodology is demonstrated through the specification of a spacecraft high gain antenna pointing mechanism for a hypothetical outer planet exploration mission.
A model-driven approach to real-time software systems development enables the conceptualization of software, fostering a more thorough understanding of its often complex architecture and behavior while promoting the documentation and analysis of concerns common to real-time embedded systems such as scheduling, resource allocation, and performance. Several modeling languages have been developed to assist in the model-driven software engineering effort for real-time systems, and these languages are beginning to gain traction with practitioners throughout the aerospace industry. This paper presents a survey of several real-time software system modeling languages, namely the Architectural Analysis and Design Language (AADL), the Unified Modeling Language (UML), Systems Modeling Language (SysML), the Modeling and Analysis of Real-Time Embedded Systems (MARTE) UML profile, and the AADL for UML profile. Each language has its advantages and disadvantages, and in order to adequately describe a real-time software system's architecture, a complementary use of multiple languages is almost certainly necessary. This paper aims to explore these languages in the context of understanding the value each brings to the model-driven software engineering effort and to determine if it is feasible and practical to combine aspects of the various modeling languages to achieve more complete coverage in architectural descriptions. To this end, each language is evaluated with respect to a set of criteria such as scope, formalisms, and architectural coverage. An example is used to help illustrate the capabilities of the various languages.
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