History and Inspiration¶

Intro¶

There have been many astrodynamics libraries developed over the years, each with its own strengths and weaknesses. Brahe draws inspiration from several of these projects while aiming to provide a unique combination of features, performance, and usability.

History¶

The origins of Brahe started in 2014 when I first started graduate school at Stanford. At the time, I was working on a project that required high-fidelity orbit propagation and I found that high-fidelity tools were either inaccessible (proprietary, expensive, or both) or difficult to use (poor documentation, complex APIs). I wanted to create a tool that was both powerful and easy to use to make it easy for researchers and engineers to ask and answer questions they really cared about without needing to become experts in astrodynamics or software engineering themselves.

As I changed organizations and projects over the years, I kept running into the same problem of a lack of open, permissively license, astrodynamics software. So when I joined a new organization I'd write a new astrodynamics library using the core algorithms and data structures in new languages to make astrodynamics accessible to those organizations. Through this process, I kept refinding my approach to the software design --- learning and improving with each iteration.

When I returned to finish my PhD in 2019, I decided to take the best parts of these previous implementations and create a new library from scratch that would be open and accessible to all so that others wouldn't have to go through the same process of reinventing the wheel. In 2023 I began rewriting the library in Rust to take advantage of its performance, safety, and modern language features. The result is Brahe as it exists today.

Inspirations and Alternatives¶

FastAPI¶

FastAPI isn't an astrodynamics library at all, but it is one of the primary inspirations for Brahe's design. FastAPI is a modern web framework for building APIs with Python. It is designed to be easy-to-use, high-performance, and scalable. I find it's design to be an elegant mix of minimalism and extensibility which makes it easy to get started with while still being powerful enough for complex applications.

It's incredibly well documented and distributed through common package managers which makes it easy to install and integrate into new projects. It also has a strong focus on type hints and data validation which helps catch errors early and improves code readability. All of these design principles influenced Brahe's design.

Pydantic¶

Pydantic is another non-astrodynamics library that influenced Brahe's design. Pydantic is a data validation and settings management library for Python. It uses Python type hints to define data models and provides automatic validation and serialization of data.

Pydantic uses a Rust core for performance with Python bindings which influenced my decision to use Rust for Brahe's core implementation. As with FastAPI, Pydantic is well-documented and distributed through common package managers which makes it easy to install and integrate into new projects.

STK (Systems Tool Kit)¶

Systems Tool Kit (STK) is likely the most well-known commercial astrodynamics software package. It is extremely well validated and provides built-in visualization capabilities. It also supports a wide variety of use-cases and has workflows for built-in analysis. However, it is expensive and closed-source which limits its accessibility and extensibility.

FreeFlyer¶

FreeFlyer is another commercial astrodynamics software package. It has been used for trajectory design and mission analysis for many high-profile space missions. It is also known for its scripting capabilities. a.i. Solutions generously provides free licenses for academic users. However it is closed-source which can limit its accessibility and extensibility.

Orekit¶

Orekit is a popular open-source astrodynamics library written in Java. It provides a wide range of features, is well-validated, and well-documented. There are also Python bindings available through different wrappers, though all require a Java runtime.

While Orekit is powerful, its Java foundation makes it difficult to integrate into modern Python scientific computing ecosystem. I also found that due to it's Java roots it uses many design patterns such as factory methods that can make it hard to figure out where in the codebase to look for certain functionality to understand how things work.

I appreciate Orekit's permissive open-source licensing (Apache 2.0) which allows for both academic and commercial use, modification, and distribution, which influenced my decision to license Brahe under the MIT License.

GMAT (General Mission Analysis Tool)¶

GMAT is an open-source astrodynamics software package developed by NASA. It provides a wide range of features and is well-validated. It also provides a custom scripting language for mission design and analysis.

GMAT documentation can be hard to find and navigate which made it hard for me to learn. It is also distributed as it's own standalone application, as opposed to a common library, which makes it difficult to integrate into new software.

poliastro¶

poliastro is an open-source astrodynamics library written in Python. It is designed to be easy-to-use and integrates well with the scientific Python ecosystem. It provides a wide range of features for orbit propagation, maneuver planning, and mission design. It is well-documented with many examples and tutorials, though is no longer actively maintained.

Skyfield¶

Skyfield is an excellent open-source library for high-precision astronomy and satellite tracking written in Python. It is designed to be easy-to-use and provides accurate calculations for positions of planets, stars, and satellites. It is well documented, with lots of examples and well-maintained.

It primarily focuses on ephemeris calculations and star tracking for astronomy, but also supports satellite orbit propagation using two-line element (TLE) data.

Nyx Space¶

Nyx Space is a modern astrodynamics library written in Rust with python bindings. It focuses on validation and verification of its algorithms and provides high-performance implementations of common astrodynamics tasks. It's general focus in on trajectory design and orbit determination for interplanetary missions, though it also supports Earth-orbiting missions as well.

Nyx Space is licensed under an AGPLv3 license which requires derivative works to also be open-sourced under the same license, which can limit its use in commercial applications. Commercial licenses are available from Nyx Space for those who want to use it in closed-source applications.

Basilisk¶

Basilisk is an open-source astrodynamics and spacecraft simulation framework developed by the Autonomous Vehicle Systems (AVS) Lab at the University of Colorado Boulder. It provides a modular architecture for simulating spacecraft dynamics, control systems, and mission scenarios though a component-based approach.

Basilisk is primarily focused on spacecraft simulation and control system design, making it well-suited for simulating complex spacecraft missions with multiple interacting subsystems. However it is not distributed through common package managers which can make it difficult to integrate into new software projects.