Modeling and Simulation of Satellite Based Systems

Herpel, H.-J.
herpel@space-elec.dofn.de
DASA/Dornier

Abstract:
Satellite based systems (e.g. navigation, communication, earth
observation, reconnaissance, science) are an emerging application domain
that requires advanced system design methods and tools to meet todays
design-to-cost and time-to-market requirements.  Therefore, Dornier
Satellitensysteme GmbH has defined EaSyVaDe, a methodology for Early
System Validation of Design which supports all phases from requirements
analysis down to implementation.  The associated tool environment (SBSlab)
enables system designers to describe, analyze, optimize, and validate
system concepts and refine it down to a level which can be used as input
to the implementation phase.

The EaSyVade life cycle approach is based on evolutionary prototyping.
This means the construction of an executable system model to enhance
understanding of the problem.  At each refinement step an executable model
is generated and checked against its requirements.  This includes
functional, performance, and user interface aspects.  Thus, early feedback
between customers and designers is possible, and time consuming redesign
cycles can be eliminated.

The EaSyVaDe methodology is supported by an integrated set of tools called
SBSlab (= Satellite Based Systems laboratory).  The tool set supports
system engineers in the validation of specifications and design space
exploration for satellite based systems.  During the system specification
phase SBSlab helps to create an executable system prototype from given
user requirements.  Thus, SBSlab enhances understanding of the system's
intended behavior and allows to check it against the customers
specification. During the design modelling phase SBSlab allows to refine
the initial system model down to implementation level.  This includes
algorithm development, architecture-compliant modelling and C/Ada code
generation for a specified target processor or generation of VHDL.
SBSlab is library based.  For each of the basic building blocks of
satellite based systems (ground/control segment, space segment, user
segment) a set of library elements (e.g. TM/TC interface, CCSDS packet
generator, data handling, AOCS, navigation payload, communication
channels) is provided.  These domain specific library elements can be used
together with the tool specific library elements to create a model of
satellite based systems.

The library based approach is a very fast route to generate executable
specifications.  New elements, also user coded blocks can be added easily.
Thus, a maximum of reusability is achieved.  Typical applications of SBSlab
include:
  - Defmition and analysis of satellite constellations with respect to
    coverage, availability and integrity.
  - Modelling and simulation of spacecraft (autonomy functions, onboard data
    handling, AOCS, power distribution unit, etc.)
  - Modelling and simulation of satellite payloads (e.g. navigation,
    communication, image processmg
  - Modelling of transmission channels.
  - Modelling and simulation of operational aspects between space and ground
    segment.
  - Modelling and simulation of data processing on ground.
  - Modelling and simulation of specific user's behaviour (e.g. aircraft,
    car, train).
  - Development and verification of user specific data processing
    components (e.g. satellite receiver for navigation).

EaSyVaDe is an effective method to reduce risk on satellite projects by
early focus on feasibility analysis, and the identification of a realistic
and manatory set of system requirements.  The ability to transform the
validated models into production code for the target suystem is the key
factor in reducing the life cycle time costs.
Several applications of EaSyVaDe for onboard satellite subsystems have
shown the advantages of the approach concerning risk reduction and savings
in cost and time.  Presently the methodology is applied to a new satellite
based radio navigation system.