Proceedings of IDMME – Virtual Concept 2010 Bordeaux, France, October 20 – 22 2010
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Enabling Collaborative Conceptual Design for Space Systems Projects
Walter A. Dos Santos1, Alan Hardwick2, Bruno B. F. Leonor1 and Stephan Stephany1
(2): Birkbeck College, School of Computer Science and Information Systems University of London, UK +44 130 671346 E-Mail:
[email protected]
(1): INPE National Space Research Institute, Sao Jose dos Campos, Brazil +55 12 3945 6622/ 3941 1890 E-Mail:
[email protected],
[email protected],
[email protected] Abstract: Space systems engineering demand coordinated expertise from different disciplines. Furthermore, satellite systems are growing even more complex making conceptual design a key driver for cost and deadline. When poorly performed, various problems may arise. One solution is to underpin this project phase with a collaborative systems engineering environment and by adoption of a model-driven engineering approach (MDE) where models are the main artefact during system development. This work reports the development and application of a novel knowledge-based software tool, named SatBudgets, that employs satellite SysML (Systems Modelling Language) models and web services. This enables information reuse, collaboration and integration to deal with interdisciplinary nature of this problem domain in an extended enterprise environment.
as Phase A, become more important and difficult. Conceptual design maps client needs to product use functions and is where functional architecture (and sometimes the physical architecture) is decided upon. Typically, the design specifications and constraints impose a heavy burden on systems-of-systems engineering and particularly on requirements engineering which drives the whole system's life cycle. Henceforth, taking suitable decisions at this project phase ends up paying dividends with schedule, performance, cost and risk. This work is focused on the preliminary conceptual satellite design with computer-based information reuse and integration in order to deal with the interdisciplinary nature of the domain via an MDE approach implemented with SysML as a satellite architecture description language. This enables information reuse between different satellite projects as well as facilitating knowledge integration and management over systems engineering activities.
Key words: SOA, SysML, Systems Engineering, Information Reuse and Integration, Collaborative Work.
For demonstration purposes, only the early budgeting workflow of conceptual design is illustrated in this work. This is performed using a novel knowledge based software tool, named SatBudgets [DL1]. SatBudgets uses XML Metadata Interchange (XMI) information exchange between a satellite SysML model and its initial requirements budgetings via a rule-based knowledge database captured from satellite subsystems experts. Furthermore, in order to enable collaboration among project partners, web services are directly invoked by SatBudgets.
1 Introduction
With advances in computer networking applications, recent interest in collaborative environments for supporting a large spectrum of workgroup activities has been rising in the literature. Space systems engineering require essentially multidisciplinary expertise ranging from onboard computing to launcher vehicle interfacing. This cooperation is made more difficult if the required expertise is spread across a number of sites, and is rendered even more so if the satellite is a multi-national collaboration. Factors such as time zone differences, language barriers, numbering and units of measurement conventions, and different IT platforms can all have an adverse effect on the project timeline and budget.
The work is organized as follows. Section 2 presents a short introduction to SysML as an architecture description language and Service Oriented Architectures. Section 3 surveys previous research in the area. Section 4 shows the SysML satellite modelling. Section 5 introduces the software tool SatBudgets and covers the Satellite Collaborative Systems Engineering. Section 6 describes further future work. Finally, Section 7 summarizes this research report.
As space system designs are growing more complex, technical issues related to concepts development, also referred IDMME_P154
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2 Background
For instance, on previous INPE satellite projects, the required electrical capacity for batteries is derived primarily from the power budgeting and orbital parameters of mission statement since batteries are used during eclipse times to provide power. Nevertheless, this is also coupled to others budgetings like mass, structure, etc. The lessons learned from these chained updates, due to coupling issues, justify per se a collaborative MDE approach to the conceptual design.
2.1 The ITASAT Satellite Project
Briefly posed, a satellite has generally two main parts: (1) The bus or platform where the main supporting subsystems reside; and (2) The payload, the part that justifies the mission. This works targets the ITASAT satellite whose general architecture is depicted in Figure 1 and includes: (a) The ITASAT satellite with the Data Collection System (DCS) and experimental payloads (space segment); (b) The existing Tracking, Telemetry and Command (TT&C) ground segment with Cuiab¶a and Alcantara tracking stations and (c) The existing Data Collection ground segment, including the Data Collection Platforms (DCP) networks.
2.2 SysML Architectural Description
System modelling based on an architecture description language is a way to keep the engineering information within one information structure hence a good approach for the space systems engineering due to its intrinsic interdisciplinary nature. Architectures represent the elements implementing the functional aspect of their underlying products. The physical aspect is sometimes also represented, for instance when the architecture represents how the software is deployed on a set of computing resources, like a satellite. SysML is a domain-specific modelling language for systems engineering and it supports the specification, analysis, design, verification and validation of various systems and systems-ofsystems [S2]. It was developed by the Object Management Group (OMG) [O1] in cooperation with the International Council on Systems Engineering (INCOSE) [I1] as a response to the request for proposal (RFP) issued by the OMG in March 2003. The language was developed as an extension to the actual standard for software engineering, the Unified Modelling Language (UML) [U1] also developed within the Object Management Group (OMG) consortium.
Figure 1: ITASAT System general architecture [DL1].
The ITASAT satellite is part of the Small Technological Satellite Development Program funded by Brazilian Space Agency (AEB) with technical coordination of INPE and academic coordination of the Aeronautics Institute of Technology (ITA).
Basically, SysML is used for representing system architectures and linking them with their behavioural components and functionalities. By using concepts like Requirements, Blocks, Flow Ports, Parametric Diagrams and Allocations, it is simple to achieve a profitable way to model systems. A comparison between SysML1.0 to UML2.0 in term of reuse is presented in [S2]. Requirements, Parametrics and Allocations are new diagrams available only in SysML. Activity and Block diagrams are reused from UML2.0 and extended in SysML. Finally, State Machines, Interactions and Use cases are reused from UML2.0 without modifications.
The ITASAT Mission entails the development, the launch and the operation of a small university satellite for use in a low Earth and low inclination orbit, capable of providing operational data collection services to the Brazilian Environmental Data Collection System (DCS), besides testing in orbit experimental payloads.
2.3 Extended Enterprises via SOA
The Systems Engineering approach taken is formal and systematic since the great complexity requires this rigor. Another feature of systems engineering is its holistic view and it involves a top-down synthesis, development, and operation.
As organizations grow, they acquire an ever-increasing number of applications distributed across a number of departments and sites. At the same time, it is becoming increasingly important for organizations to efficiently share information between these applications. SOA arose out of this need to allow intercommunication between applications [E2]. SOA entails developing loosely coupled interfaces to applications (services), which can be used to access the applications and exchange information. By combining these services, it is possible to develop adhoc applications (mashups) as required.
This rationale for detailed design follows a N-Tiered development and organization of requirements. This process generates the ITASAT Specification and Documentation Tree and also implicitly generates a highly coupled requirements tree, which complicates somewhat systems engineering trade studies so far being manually performed.
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The authors of this present work claim that the MDE approach for a satellite project underpinned by SysML modelling and in a collaborative environment enables the realization of extended enterprises.
The concept of Extended Enterprises [R1] describes a scenario where a loosely coupled, self-organizing network of business partners coordinate their capabilities to generate products and services offerings to the third parties. Businesses in the extended enterprise may operate either independently, typically through market mechanisms, or cooperatively via agreements and contracts.
4 Conceptual Satellite Design via SysML
The formal Systems Engineering approach suggests the decomposition of the system into subsystems and further into components [D1].
Even though web services are a direct extension of existing Internet technology, its effects on the enterprise world are quite relevant. The Web services and SOA provides dramatic business performance improvements enabling cost reduction and business agility.
Space Systems Engineering is a subclass of that previously mentioned in the sense that it is primarily concerned with space systems, e.g. satellite systems [LW1].
It is possible to bring new life to legacy applications by creating a service interface, making its functionality available to a wider audience, providing a major financial benefit for an organization, as applications can be created by the orchestration of services to existing applications, rather than developing systems from scratch.
The satellite conceptual stage follows the transformation of customer needs into product functions and use cases and precedes the design of these functions across the space engineering disciplines: typically, mechanical, electrical, software, etc. This work argues that MDE is quite suitable for information reuse and integration for the domain of Space Systems Engineering.
In the collaborative environment described later in this work, it is expected that many of the applications running on local servers will be transferred to project partners. Their applications then may have their own evolution as a natural effect of the space program maturity as third parties in the marketplace start to design and manufacture space components.
MDE is the systematic use of models as primary engineering artefacts throughout the engineering lifecycle [S1]. MDE can be applied to software, system, and data engineering. MDE technologies, with a greater focus on architecture and corresponding automation, yield higher levels of abstraction product development. This abstraction promotes simpler models with a greater focus on problem space. Combined with executable semantics this elevates the total level of automation possible.
By outsourcing some of these business functions that had been previously self-provided, institutions may keep their "core competencies" which uniquely determine the firm's value proposition and concentrate their resources on those investments and activities that provide them the greatest added value.
SysML allows incrementally refinable description of conceptual satellite design and product architecture. This helps systems engineers who are concerned with the overall performance of a system for multiple goals (e.g. mass, cost, and power). The systems engineering process methodically balances the needs and capabilities of the various subsystems in order to improve systems performance.
3 Related Work
Some past approaches to model-driven engineering and related issues have been reported in the literature [MP1] [B1] [S1] [SV1].
SysML elements in the design represent abstractions of artefacts in the various engineering disciplines involved in the development of the system. The design represents how these artefacts collaborate to provide the product functionalities.
In the industrial domain, various initiatives on collaborative environment have been published. A collaborative framework to support space systems engineering is presented in [D2]. A Knowledge-driven and web-based system architecture for collaborative product development is introduced in [RA1]. Using concurrent engineering, alternative models are used in [LL1] for Conceptual Satellite Design. The work in [AD1] shows a space systems concurrent design where engineers and customers work together to design new space systems. Models for Next Generation Concurrent Engineering are presented in [M1]. Finally, in [GE1] and [SE1] a Model based Design and a concurrent design facility using web services are described.
The size, volume, and mass constraints often encountered in satellite development programs, combined with increasing demands from customers to get more capability into a given size, make systems engineering methods particularly important for this domain. SysML diagrams allow information reuse since they can be employed in other similar satellite projects by adaptation and dealing with project variabilities. An exploration of these features for the onboard software design of satellites is shown in [D3].
Applications of SysML for MDE are presented in the following works [B1], [SV1]. In [C1] a SysML spacecraft architecture framework for small satellites is discussed.
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SysML allows the utilization of use case diagrams which were inherited from the UML without changes [B1]. Use case diagrams are employed to describe systems functionalities by 3
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its actors looking forward to achieving a system goal. On its turn, the SysML block diagram is used to show features and high level relationships. It is used to allow systems engineer to separate basically the responsibilities of the hardware team from the software team.
currently runs as a standalone Java application under the Eclipse IDE [E1] which already supports SysML as a plug-in. 5.2 Requesting SatBudgets Web Services
Collaborative Computing is an umbrella term that encompasses a range of technologies. Web Services are a valuable tool within the concept of collaborative computing and they have traditionally used XML to transmit messages. The XML that is used is based on the SOAP (Simple Object Access Protocol) standard. One of the strengths of web services conferred by using XML as the messaging language is platform independence.
A complete description of the Model-Driven Requirements Engineering Approach for the ITASAT project can be found in [DL1]. The requirements diagram plays a key role into the SysML model as requirements present in this diagram can also appear in other SysML diagrams linking the problem and solution spaces.
Web services have 3 main components: (1) The Consumer (or Service Requestor) - this is normally the end-user; (2) The Service Provider the repository of services called by the consumer and (3) The Service Broker the services that are available to the consumer are published in the broker library.
5 Enabling Satellite Collaborative Systems Engineering
As part of the breakdown activities, subsystems may be assigned to different teams that could be co-located or distributed between research institutions and industries according to the Extended Enterprise concept. This is accomplished by using a distributed application, SatBudgets, which in this work was restricted for budgetings.
If a consumer requires a service, it must discover the service in the broker directory, via a WSDL message (web service description language) [E2]. If the service is available, the consumer will bind to the service provider and execute the service (messages will be exchanged via SOAP). This project uses a XML/SOAP based web service.
5.1 The SatBudgets software Tool
After requirements analysis, starts the performance budgeting phase. As a case study, this work describes how a software tool, named SatBudgets, supports XMI information exchange between a satellite SysML model and its initial requirements budgetings. The SatBudgets workflow is shown in Figure 2 and its software engineering activities are described in [DL1].
In order to test the initial prototype, the deployment machine was chosen to be the same as the development machine. Due to the platform independence of Java and XML, they were chosen so that the application can be deployed to a variety of operating systems. For the development of web service and web broker applications, this entailed developing both parts of a web service application: the web service and the client consumer application. The development and local deployment of SatBudgets Services involved development and local deployment/testing of some of the functionality required by SatBudgets. In this instance, the services provided by third parties were the evaluation of the required numbers Thermistors, the number of Direct Command and the size of solar panels required to power the satellite as configured. The Web Service Request Processing Sequence Diagram is shown generically in Figure 3. There are various ways in which this can be accomplished; nevertheless this brings to a crucial point in planning for SOA: granularity.
The deployment of services to a remote site, since the application is developed in Java, had no compatibility issues. Once the service has been deployed, it should be possible to consume these services by ensuring the client application has the correct WSDL URL, although connection will be dependent on any firewall or other access restrictions in place.
Figure 2: SatBudgets workflow using Extended Enterprises.
The SatBudgets workflow has the following sequence of events is: (a) An XMI file exported from the SysML modeling is read; (b) Parsing of key modelling parameters is performed; (c) Satellite Systems Engineering business rules are applied to infer performance budgetings; and (d) A final report is generated for systems engineers via a free Java report generator framework. The SatBudgets tool links a SysML satellite model to budgetings, some of them invoked via web services. The tool IDMME_P154
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Furthermore, the described collaborative MDE approach with a SysML satellite architecture description caters for project information reuse as well as knowledge integration and management. This work will be gradual and incrementally extended to introduce MDE automation concepts into the ordinary systems engineering workflow of a university satellite called ITASAT under development. 8- References
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Figure 3: SatBudgets collaborative flow of information.
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6 Future Work
Currently a benchmark analysis for the SatBudgets tool results is being performed. An upgrade to the tool will incorporate some additional functionalities, namely: - Model Round-tripping - changes to the spreadsheet will affect SysML model and vice-versa; - Provide Database and web client support; - Enhance the database repertoire for Satellite Systems Engineering business rules; - Provide an interface to SatBudgets for Eclipse IDE aggregation and - Provide an interface to SatBudgets for docking to an in-house Satellite Simulator.
[C1]. Casanova, P.Y.: Implementation of a Spacecraft Architecture Framework for Small Satellites. TU Mnchen, Diploma Thesis (2007) [D1]. Dieter, G. E.: Engineering Design a Materials and Processing Approach. McGraw Hill International Edition (1991) [D2]. Dos Santos, W. A.:A Collaborative Framework to Support Space Systems Engineer ing. In: XII Chilean Congress on Electrical Engineering, Temuco, Chile, pp.574578, 1997. [D3]. Dos Santos, W. A.: Adaptability, Reusability and Variability on Software Systems for Space On-Board Computing. ITA Ph.D. Thesis (2008)
7 Conclusions
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Due to its very complex and multi disciplinary nature, the flawless design, construction and launching of satellites is quite demanding. Experts from many fields are required to cooperate to ensure the success of the project. This demands strong systems engineering to deal with systems-of-systems complex issues, manufacturing demands and keep risks manageable.
[E1]. Eclipse IDE: http://www.eclipse.org/
Some projects may acquire an ever-increasing number of partners which run applications distributed across a number of departments and sites. This requires efficient ways to share information making. Hence various organisations within the space exploration and satellite construction industry have been researching concurrent engineering and collaborative computing technologies to deal with some of these issues.
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In this work, an application that uses SysML satellite modelling and a novel knowledge based software tool, named SatBudgets to support preliminary collaborative conceptual design of satellites by either locally or remotely processing initial budgetings. SOA and web services were the underlying technologies to implement an extended enterprise scenario. This allows outsourcing some of basic business processes previously self-provided by institutions enabling them to concentrate on their core business with a larger return on investment. IDMME_P154
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[LW1]. Larson, W. J. and Wertz, J. R. Space Mission Analysis and Design. McGrawHill (2004) [LL1]. Lewis,B. and Lang, J. and Jolly, R.: Modular Concurrent Engineering Models: Enabling Alternative Models in Conceptual Satellite Design. In: The 2007 IEEE Aerospace Conference, 2007.
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[MP1]. Mazon, J. N. and Pardillo, J. and Trujillo, J. A ModelDriven Goal-Oriented Requirement Engineering Approach for Data Warehouses. ER 2007 workshops [M1]. Morse, E. and et al.: Next Generation Concurrent Engineering: Developing Models to Complement Point Designs. In: The 2006 IEEE Aerospace Conference, 2006. [O1]. OMG: Object Management Group. http://www.omg.org [RA1]. Rodriguez, K. and AlAshaab, A.: Knowledge webbased system architecture for collaborative product development. Computers in Industry Vol. 56 (2005) pp. 125140, Elsevier B.V., 2005. [R1]. Ross, J. and et al.: Enterprise Architecture As Strategy: Creating a Foundation for Business Execution. Cambridge, Harvard Business School Press (2006) [SE1]. Scheuble, M. and Eisenmann, H. and De Wilde, D.: Concurrent Engineering and Model based Design. In: Concurrent Engineering for Space Applications Workshop, 2004. [S1]. Schmidt, D. C.: ModelDriven Engineering. IEEE Computer (2006) [SV1]. Soares, M. dos S. and Vrancken, J.: Model-Driven User Requirements Specification using SysML. Journal of Software (2008) [S2]. SysML: System http://www.sysml.org
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