I recently found this:

https://github.com/JuliaSpace/

Out of curiosity, what Python, Fortran, and C/C++ packages do you use / can you recommend?

Astropy [0] lives at the heart of most work. It has a Python interface, often backed by Fortran and C++ extension modules. If you use Astropy, you're indirectly using libraries like ERFA [6] and cfitsio [7] which are in C/Fortran.

I personally end up doing a lot of work that uses the HEALPix sky tesselation, so I use healpy [2] as well.

Openorb is perhaps a good example of a pure-Fortran package that I use quite frequently for orbit propagation [3].

In C, there's Rebound [4] (for N-body simulations) and ASSIST [5] (which extends Rebound to use JPL's pre-calculated positions of major perturbers, and expands the force model to account for general relativity).

There are many more, these are just ones that come to mind from frequent usage in the last few months.

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[0] https://www.astropy.org/

[1] https://healpix.jpl.nasa.gov/

[2] https://healpy.readthedocs.io/en/latest/

[3] https://github.com/oorb/oorb

[4] https://rebound.readthedocs.io/en/latest/

[5] https://github.com/matthewholman/assist

[6] https://github.com/liberfa/erfa

[7] https://heasarc.gsfc.nasa.gov/fitsio/

Thank you very much for the detailed answer!

Will look into those. I recently wrote a little n-body simulator to become familiar with Julia's DifferentialEquations.jl and that motivated me to learn more about astrodynamics.

I'm sure there are other subdomains that make use of Julia, but in particular I think if your problem involves writing an evolution-like or agent-based-model-like simulation you may find the strengths of Julia particularly compelling

“You may find” is not the same thing as “has taken off in” which was the claim