Engineering topics
Publications and source records attributed to Shames, Peter M..
Model-based systems engineering (MBSE) is intended to improve how systems engineering is performed compared with a more traditional document-based approach by effectively using models to analyze, specify, design, and verify systems. The OMG Systems Modeling Language (OMG SysML™) enables the practice of MBSE by providing a robust and expressive language for representing systems.
Space data systems are inherently complex. They are systems-of-systems, typically composed of spacecraft and mission operations systems (MOS) belonging to one (or more) organizations, and multi-mission communication assets belonging to other organizations. In many cases, the spacecraft contain sub-systems and instruments provided by different organizations, and MOS systems that may be developed and operated by other organizations. The point of greatest leverage in system architecting is at the interfaces. We have developed a set of methods for using SysML to model systems-of-systems and their interfaces. This paper describes how to apply this method to space data systems at a variety of levels of detail, from abstract systems and subsystems down to hardware and software components, including the details of their interfaces and protocol designs.
End-to-end space communication architectures must connect system elements that may be in space, on the ground in mission operations centers, or are shared assets such as ground communications stations. End-to-end connectivity involves space communications over RF links, but also cross support services, terrestrial network circuits, and a variety of application layer protocols for commanding, telemetry, and mission operations. CCSDS has developed a large suite of interoperable, and cross-supportable, protocols for these purposes. Each of these defines a specific “layer” of functionality, such as: RF modulation, space link error coding, cross support frame delivery, or network layer routing. CCSDS has recently published a Space Communication Cross Support Architecture Requirements Document (SCCS-ARD) that describes how many of these standards fit together and how they are intended to be used. This paper provides an overview of this document, presented so as to explain the concepts so that others may use them. These concepts will be described from several key viewpoints.
End-to-end space communication architectures must connect system elements that may be in space, on the ground in mission operations centers, or are shared assets such as ground communications stations. End-to-end connectivity involves space communications over RF links, but also cross support services, terrestrial network circuits, and a variety of application layer protocols for commanding, telemetry, and mission operations. CCSDS has developed a large suite of interoperable, and cross-supportable, protocols for these purposes. Each of these defines a specific “layer” of functionality, such as: RF modulation, space link error coding, cross support frame delivery, or network layer routing. CCSDS has recently published a Space Communication Cross Support Architecture Requirements Document (SCCS-ARD) that describes how many of these standards fit together and how they are intended to be used. This paper provides an overview of this document, presented so as to explain the concepts so that others may use them. These concepts will be described from several key viewpoints.
Communications between systems is often initially represented at a single, high level of abstraction, a link between components. During design evolution it is usually necessary to elaborate the interface model, defining it from several different, related viewpoints and levels of abstraction. This paper presents a pattern to model such multi-layered interface architectures simply and efficiently, in a way that supports expression of technical complexity, interfaces and behavior, and analysis of complexity. Each viewpoint and layer of abstraction has its own properties and behaviors. System elements are logically connected both horizontally along the communication path, and vertically across the different layers of protocols. The performance of upper layers depends on the performance of lower layers, yet the implementation of lower layers is intentionally opaque to upper layers. Upper layers are hidden from lower layers except as sources and sinks of data. The system elements may not be linked directly at each horizontal layer but only via a communication path, and end-to-end communications may depend on intermediate components that are hidden from them, but may need to be shown in certain views and analyzed for certain purposes. This architectural model pattern uses methods described in ISO 42010, Recommended Practice for Architectural Description of Software-intensive Systems and CCSDS 311.0-M-1, Reference Architecture for Space Data Systems (RASDS). A set of useful viewpoints and views are presented, along with the associated modeling representations, stakeholders and concerns. These viewpoints, views, and concerns then inform the modeling pattern. This pattern permits viewing the system from several different perspectives and at different layers of abstraction. An external viewpoint treats the systems of interest as black boxes and focuses on the applications view, another view exposes the details of the connections and other components between the black boxes. An internal view focuses on the implementation within the systems of interest, either showing external interface bindings and specific standards that define the communication stack profile or at the level of internal behavior. Orthogonally, a horizontal view isolates a single layer and a vertical viewpoint shows all layers at a single interface point between the systems of interest. Each of these views can in turn be described from both behavioral and structural viewpoints.