Open-SESSAME Framework

Introduction

An important aspect of dynamic analysis and control design is developing simulations. However, students and engineers are rarely exposed to large-scale, advanced, or reusable simulation concepts, but instead are relegated to reinventing simple simulations for each and every investigation. There are numerous software packages that provide simulation capabilities, but these lend little insight into the operation of modeling code or allow the user complete freedom in developing their own models.

Therefore, the Space Systems Simulation Laboratory has kicked off an open-source project developing a spacecraft simulation framework to provide students and engineers the tools for satellite dynamics and controls analysis and a basis for implementing spacecraft models.
The Open-Source, Extensible Spacecraft Simulation And Modeling Environment (Open-SESSAME) is a collection of libraries, toolkits, and extension points that provide a framework for creating and analyzing spacecraft models of varying complexity. The framework is open-source, so users can examine and modify the source code without worrying about copyrights or proprietary information. The collection of tools also includes other open-source projects that already include a broad user support base. The framework is extensible by allowing users the ability to provide added functionality and models and propagate these extensions back to the user community through a publicly hosted repository.

Students and engineers are encouraged to download and use the Open-SESSAME Framework by checking out the Sourceforge Repository.

Design & Functional Requirements

• A collection of libraries to assist in the analysis of spacecraft operations
• A Framework for combining these libraries and toolkits together to represent the full simulation of a spacecraft in flight
• An instructional example for developing future simulation software
• Extension points for adding new models and simulation capabilities to the framework

Framework Components

There are numerous components of the framework, with the ability to add more as necessary. The following are the main components of the framework and a short description of their functionality:

• Matrix Library - vector and matrix container classes for representing and manipulating linear algebra operations
• Rotation Library - library of coordinate frame representations and operations (ie quaternions, direction cosine matrices, etc.)
• Attitude Toolkit - collection of rigid-body attitude representations, kinematics, and dynamics
• Orbit Toolkit - collection of orbital representations, dynamics and operations
• Environment - models of environmental characteristics affecting a spacecraft (ie gravity, atmospheric drag, solar radiation pressure, magnetic fields)
• Integrator Library - numerical integration techniques (ie Runge-Kutta, Adams-Bashforth, Cubic-Spline interpolation)
• Export Components - for exporting simulation results to other software packages (ie gnuplot, AGI SatelliteToolkit, Mathwork's MatLab, Microsoft Excel) for further analysis and display.
• Server Components - components for running the simulator as a server, allowing for distributed processing, hardware-in-the-loop testing, and flight software verification.

Example Uses

• Simulating the attitude of a spacecraft with momentum wheels using a linear controller.
• Analyzing the orbital degradation of the space station due to pertubations.
• Verifying flight software on the bench.
• Providing a simulation environment for testing hardware-in-the-loop components or hardware spacecraft simulators.