Aerospace and Electronic Systems Magazine April 2018 - 25

systems and subsystems. By defining the parametric diagram for
system sizing and efficiency measuring, a tradeoff study is explored.
Romero and Ferreira [4] have used SysML to model attitude
and orbit control system (AOCS) software for a satellite using
SysML. Constraints and parametric diagrams for the AOCS subsystem are depicted and explained. Physical aspects are modeled
using sequence diagrams. Finally, model is refined to become a
platform specific model (PSM) from software viewpoint, allowing
code generation.
In the literature, the model-based approach is compared with
the document-based approach. This develops a sense that the
MBSE is a paradigm shift that contradicts the document-based SE
approach. This is one of the reasons the model-based approach is
less accepted by conventional system engineers. The documentbased approach may be inefficient in certain aspects that can be
improved by employing the MBSE approach, making the practice
of SE more effective. We therefore advocate a hybrid modeling approach as described in subsequent sections, which is assisting our
conventional SE process in the most appropriate way.

MBSE METHODOLOGY
A methodology is defined as the collection of processes, methods,
and tools used to support a specific discipline [12]. The notion of
MBSE methodology can be characterized as the collection of related processes, methods, and tools used to support SE in a modelbased paradigm. Several MBSE methodologies are in practice, as
surveyed in [12]. The system engineers can tailor one or more of
the candidate MBSE methodologies into their internal SE process
model.

OBJECT-ORIENTED SE METHOD OVERVIEW
The object-oriented systems engineering method (OOSEM) is
one of the leading MBSE methodologies. OOSEM provides an
integrated framework that combines object-oriented techniques, a
model-based design approach, and traditional top-down, waterfallstyle SE practices. It is widely advocated as an example of MBSE
best practice.
The OOSEM integrates a top-down, model-based approach that
uses OMG SysML to support the specification, analysis, design,
and verification of systems. OOSEM leverages object-oriented concepts with more traditional top-down SE methods and other modelAPRIL 2018

ing techniques to help design more flexible and extensible systems
that can accommodate evolving technology and changing requirements. OOSEM is also intended to ease integration with object-oriented software development, hardware development, and testing.
OOSEM uses a model-based approach to represent various
artifacts generated by the development activities, using OMG
SysML as the predominant modeling language. As such, it enables
the systems engineer to precisely capture, analyze, and specify the
system and its components and ensure consistency among various
system views. The modeling artifacts can also be refined and reused in other applications to support product line and evolutionary
development approaches.

ADOPTED MBSE METHODOLOGY
We have adopted an OOSEM-based hybrid approach that leverages object-oriented techniques and a SE foundation. This was
chosen after numerous deliberations on candidate methodologies
listed in the 2008 INCOSE survey [12], as well as some additional
methodologies identified as gaps since 2008. The methodology fits
with the evolutionary nature of our projects and their life cycles
within the organization. Integration with object-oriented software,
hardware, and other engineering methods is possible through
OOSEM. In addition, the system-level reuse and design evolution
is supported in OOSEM. An ample number of resources were also
available in OOSEM compared to other methodologies.
OOSEM-based methodology as adopted is depicted in Figure
1, showing satellite design and development project activities,
along with corresponding modeling artifacts used.
Phase 0 and phase A are mission definition and requirement
analysis phases. After these phase requirements, baseline is the final outcome. MBSE artifacts used during this process are SysML
requirement diagrams and use-case diagrams. Phase B involves the
preliminary design and finalization of technology choices. The outcome of phase B is the baseline system design definition. SysML
BDDs, use-case diagrams, and parametric diagrams are frequently
used in phase B. Phase C involves detailed design and manufacturing of the engineering and/or qualification models of the satellite, which is supported by artifacts for functional and performance
models of the satellite subsystems or units, such as SysML state
machine diagrams, activity diagrams, and sequence diagrams. Finally, in phase D, the unit, subsystem, and system are integrated
for final delivery of the product. This phase involves testing under

IEEE A&E SYSTEMS MAGAZINE

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine April 2018