The Basilisk astrodynamics software architecture is being designed to be capable of both faster-than realtime simulations, including repeatable Monte-Carlo simulation options, as well as providing real-time options for hardware-in-the-loop simulations. The Basilisk package is designed as a set of Python modules written in C/C++ which allows for the ease of scripting and reconfigurability of Python while still providing the execution speed of C/C++. The software is being developed jointly by the University of Colorado AVS Lab and the Laboratory for Atmospheric and Space Physics (LASP). The resulting framework is targeted for both astrodynamics research modeling the orbit and attitue of complex spacecraft systems, as well as sophisticated mission-specific vehicle simulations that include hardware-in-the-loop scenarios.
A companion Visualization program is called Vizard. This stand-alone program is based on the Unity rendering engine and can display the Basilisk simulation states in an interactive manner. The following image links to a video showing the basic features.
The name Basilisk was chosen to reflect both the reptilian (Python) nature of the product-design as well as a nod to the speed requirements as the South American common basilisk runs so fast that it can even run across water.
Basilisk Design Goals¶
The Basilisk framework is being designed from inception to support several different (often competing) requirements.
Speed: Even though the system is operated through a Python interface, the underlying simulation executes entirely in C/C++ which allows for maximum execution speed. For example, a goal is to simulate a mission year with sufficiently accurate vehicle 6-DOF dynamics with at least a 365x speed-up (i.e. a year in a day).
Reconfiguration: The user interface executes natively in Python which allows the user to change task-rates, model/algorithm parameters, and output options dynamically on the fly.
Analysis: Python-standard analysis products like numpy and matplotlib are actively used to facilitate rapid and complex analysis of data obtained in a simulation run without having to stop and export to an external tool. This capability also applies to the Monte-Carlo engine available natively in the Basilisk framework.
Hardware-in-the-Loop: Basilisk will provide synchronization to realtime via software-based clock tracking modules. This allows the package to synchronize itself to one or more timing frames in order to provide deterministic behavior in a realtime environment.
Scriptability: The Python user interface to the C/C++ layer relies on the Simplified Wrapper and Interface Generator (SWIG) software, a cross-platform, open-source software tasked solely with interfacing C/C++ with scripting languages. This Python layer allows the simulation to be easily reconfigured which allows the user complete freedom in creating their own simulation modules and flight software (FSW) algorithm modules. Further, the Python layer abstracts logging/analysis which allows a single compilation of the source code to support completely different simulations.
Controlled Data Flow: Simulation modules and FSW algorithm modules communicate through the message passing interface (MPI), which is a singleton pattern. The MPI allows data traceability and ease of test. Modules are limited in their ability to subscribe to messages and write messages, thus setting limitations on the flow of information and the power of modules to control data generation. The messaging system is also instrumented to track data exchange, allowing the user to visualize exactly what data movement occurred in a given simulation run.
Cross-Platform Solution: Basilisk is inherently cross-platform in nature, and is supported on macOS, Windows, and Linux systems. The Python layer, C programming language, ZeroMQ communication library and Unity visualization are active cross-platform developments.
Validation and Verification: Each simulation or FSW algorithm module has unit test that can be run automatically using py.test. Integrated scenario test validated coupled behavior between modules. Each dynamics modules has associated momentum, energy and power validation tests. This ensures the integrity of the valdiated modules as new simulation capabilities are added.
Monte-Carlo Capability: The simulation framework is capable of doing bit-for-bit repeatable Monte-Carlo runs. The simulation parameters can be disturbed through a range of distribution functions.
3D Visualization: Basilisk has an accompanying stand-alone visualization called Vizard that uses Unity to visualize the spacecraft, its orientation and orbits, the local planets, and various qualitative data and indicators for sensors and actuators. Simulation events and device faults may be triggered directly from the visualization.