AOCS Simulation Framework

The AOCS Simulation Framework is a framework for a software-only simulation for AOCS applications instantiated from the AOCS Framework. The development of an AOCS Simulation Framework is one of the follow-on projects for the AOCS Framework project. This document describes the main requirements that should be satisfied by such a simulation framework.

Basic Functionalities
Simulation Modes
Integration with AOCS Framework
Software Under Test

The first project started in February under phase II of the present contract with ESA. It is described under the Real Time Java Project web site.

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Basic Functionalities

The simulation framework should model the following basic functionalities:

Logging of simulation data
Visual displaying of simulation data
Monitoring of key simulation variables to ensure that they follow pre-defined profiles
Simulation of the environment (sensors, actuators, environment dynamics, etc)
Processing of operator commands (stop/start simulation, inject fault, override simulation variables, etc)

The above functionalities give rise to a number of major hot-spots, or points where behaviour adaptation takes place to customize the framework to the needs of a specific user. They include:

The logging medium and the variables to be logged
The display medium and the variables to be displayed
The monitoring profile and the variables to be monitored
The environment models
The operator commands

For each of these hot-spots, design patterns and adaptation mechanisms must be proposed.

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Simulation Modes

The software framework should allow simulation operation in both open- and closed-loop.

Additionally, two operational modes are foreseen that define the level at which the exchange of unit data between the AOCS under test and the environment exchange data. The AOCS Framework models external units (sensors and actuators) through proxy components that represent the external unit within an AOCS application. The unit proxy components have a plug-in component of type AocsUnithardware that models the low-level interface to the physical link between the AOCS software and the external unit.

In Unit-Based Simulation mode (or UBS mode), the exchange of unit data between the (simulated) environment and the AOCS application takes place at the level of the unit proxy components in the AOCS application. In practice, this could be done by customizing these components with dedicated AocsUnitHardware components that model the data exchanges with the simulated environment rather than with a unit physical link.

In UnitLess Simulation mode (or ULS mode), the unit proxy components in the AOCS application are by-passed and the exchange of unit data between the environment and the AOCS application is entirely through the shared data area. This operational mode is useful because it allows to perform functional tests even before the unit models have been fully defined.

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Integration with AOCS Framework

The primary requirement of the simulation framework is that it should be smoothly integrated with the AOCS Framework. The high-level structure of the AOCS Framework is depicted in the figure:

The framework is constituted by a set of so-called functionality managers (yellow blocks in the figure) that are customized at run-time by object-composition to implement the functionalities required for a specific AOCS application. The following functionality managers are foreseen:

the telecommand manager
the telemetry manager
the failure detection manager
the failure recovery manager
the manoeuvre manager
the controller manager
one or more unit triggers

The functionality managers are plugged into a scheduler (not part of the AOCS Framework) which is responsible for periodically activating it. The AOCS Framework generates component-based applications. The data flow between the framework components is through shared data areas (the data pools for cyclical data and the event repositories for asynchronous data).

The framework simulator should be integrated with the AOCS Framework in the sense that:

its basic functionalities should be implemented as additional functionality managers that are conceptually similar to the functionality managers already proposed by the AOCS Framework
data exchanges between simulation components and the AOCS components should be through shared data areas - possibly obtained by extending through inheritance the AOCS shared data area - with the exception of operation in UBS mode.

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Software Under Test

In order to increase confidence in the validity of the test results, the components of the AOCS application under test should be, as far as possible, integrated in the simulation environment without changes to their source code. When modifications to these components are necessary, they should be done by subclassing the original component and adding simulation-specific code. Behaviour modifications at application level, should be done by modifying the application instantiation code and by composing the application components with simulation-specific components.

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Last updated on Feb. 5-th 2002 by Alessandro Pasetti