Brahe

Brahe is a modern satellite dynamics library for research and engineering applications. It is designed to be quick-to-deploy, composable, extensible, and easy-to-learn. The north-star of the development is enabling users to solve meaningful problems quickly and correctly.

Brahe is permissively licensed under an MIT License to enable people to use and build on the work without worrying about licensing restrictions. We want people to be able to stop reinventing the astrodynamics "wheel" because commercial licenses are expensive and open-source options are hard to use.

We try to prioritize making the software library easy to learn, use, and verify. Many astrodynamics libraries are written with many layers of abstraction for flexibility that can make it challenging for new users to understand where the actual logic and algorithms are being executed. Brahe is written in a modern style with an emphasis on code clarity and modularity to make it easier to understand what individual functions are actually doing. This approach has the added benefit of making it easier to verify and validate the correctness of the implementation.

If you do find this useful, please consider starring the repository on GitHub to help increase its visibility. If you're using Brahe for school, research, a commercial endeavour, or flying a mission. I'd love to know about it.

We hope you find Brahe useful for your work!

Going Further

If you want to learn more about how to use the package the documentation is structured in the following way:

Learn: Provides short-form documentation of major concepts of the package.
Examples: Provides longer-form examples of how-to examples of how to accomplish common tasks.
Python API Reference: Provides detailed reference documentation of the Python API.
Rust API Reference: Provides detailed reference documentation of the Rust API.

Quick Start

Python

To install the latest release of brahe for Python, simply run:

pip install brahe

You can then import the package in your Python code with:

import brahe as bh

And do something fun like calculate the orbital-period of a satellite in low Earth orbit:

import brahe as bh

# Define the semi-major axis of a low Earth orbit (in meters)
a = bh.constants.R_EARTH + 400e3  # 400 km altitude

# Calculate the orbital period
T = bh.orbital_period(a)

print(f"Orbital Period: {T / 60:.2f} minutes")
# Outputs:
# Orbital Period: 92.56 minutes

or find the when the ISS will next pass overhead:

import brahe as bh

bh.initialize_eop()

# Download ISS TLE and create a propagator
client = bh.celestrak.CelestrakClient()
iss = client.get_sgp_propagator(catnr=25544, step_size=60.0)

# Propagate for 24 hours
epoch_start = iss.epoch
epoch_end = epoch_start + 24 * 3600.0
iss.propagate_to(epoch_end)

# Compute upcoming passes over San Francisco
passes = bh.location_accesses(
    bh.PointLocation(-122.4194, 37.7749, 0.0),  # San Francisco
    iss,
    epoch_start,
    epoch_end,
    bh.ElevationConstraint(min_elevation_deg=10.0),
)
print(f"Number of passes in next 24 hours: {len(passes)}")
# Example Output: Number of passes in next 24 hours: 5

If you want to see more examples of how to use brahe, you can find even more with full source code in the Examples section of the documentation.

Citing Brahe

If you use Brahe in your work, please cite the following paper:

@article{eddy2026brahe,
      title={{Brahe: A Modern Astrodynamics Library for Research and Engineering Applications}}, 
      author={Duncan Eddy and Mykel J. Kochenderfer},
      year={2026},
      eprint={2601.06452},
      archivePrefix={arXiv},
      primaryClass={astro-ph.IM},
      url={https://arxiv.org/abs/2601.06452}, 
}

Versioning

[!WARNING] Brahe generally follows SemVer. New patch versions should be rare. Public facing APIs should not significantly change, though may still change, especially for new features that are still being refined based on user feedback. We want to avoid the forever "0.x" versioning trap that many Rust and scientific software projects fall into, which can deter users from adopting the software.

If you need guaranteed stability you should pin your project to a specific major.minor.patch version (e.g., 1.2.3) rather than using a floating version specifier (e.g., ^1.2.0 or >=1.2.0).

License

The project is licensed under the MIT License - see the LICENSE file for details.

We want to make it easy for people to use and build on the work without worrying about licensing restrictions!

Contributing

If you find a bug, have a feature request, want to contribute, please open an issue or a pull request on the GitHub repository. Contributions are welcome and encouraged! If you see something missing, but don't know how to start contributing, please open an issue and we can discuss it. We are building software to help everyone on this planet explore the universe. We encourage you to bring your unique perspective to help make us stronger. We appreciate contributions from everyone, no prior space experience is needed to participate.

AI Usage

The development of Brahe has roots in 2014 when I first started writing astrodynamics software for my PhD. The main algorithms and code structure evolved over the years based on my own experience applying the software to both research problems and operational space missions. The core functionality of the library (time handling, reference frames, reference frame transformations, coordinate transformations) were all developed before the usage of AI tools. AI tools have since been sparingly adopted to help with improving and expanding capabilities that were on the nice-to-have feature list. They have also been used to help with writing documentation and improve code coverage. However, all results and outputs are manually reviewed, run, tested, and verified manually before being merged into the main branch.

For new contributions, we allow the use of AI-assited coding, however we expect that PRs will be manually reviewed and tested before being submitted and that all PRs follow the same standards of code clarity, modularity, and correctness as the rest of the codebase.

brahe 1.3.1