"The dynamical model of the planet motions and EPM ephemerides"
https://web.archive.org/web/20190503110456/https://www.cambridge.org/core/services/aop-cambridge-core/content/view/39F70E442F3AA20A7EED75F5E004BE1E/S1743921307011453a.pdf/div-class-title-the-dynamical-model-of-the-planet-motions-and-epm-ephemerides-div.pdf

"Nyx is a high fidelity, fast, reliable and validated astrodynamical toolkit library written in Rust."
https://gitlab.com/chrisrabotin/nyx
https://gitlab.com/chrisrabotin/nyx/blob/master/VALIDATION.md

"Space Mission Design (smd)"
https://github.com/ChristopherRabotin/smd

"Implementation of "Astronomical Algorithms" by Jean Meeus"
https://github.com/soniakeys/meeus

"GMAT is a space trajectory optimization and mission analysis system developed
by NASA and private industry"
https://sourceforge.net/projects/gmat/files/GMAT/GMAT-R2016a/
https://software.nasa.gov/software/GSC-17177-1

System IDentification Programs for AirCraft (SIDPAC)
https://software.nasa.gov/software/LAR-16100-1