[dard]

SPICE itself is a C package with a number of wrappers in other languages. JPL use it, along with numerical integrator and orbit determination code to generate SPICE "kernels", IE: binary files. The Horizons API allow you to use their numerical integrators to calculate the position of asteroids and comets. This works great for single objects, or a handful, but struggles when you want to look at the entire solar system at a time. This is where my code comes in, it enables similar calculations to what Horizon's provides, but you can do them locally on all known asteroids/comets.

The C SPICE library is available online, but it dates back decades, and was not really built with multi-core support in mind. My code enables reading of SPICE kernel files with native multi-core support. Though I would argue the bigger benefit that my code provides is the numerical integrator which can be used on the entire asteroid belt at once.

JPL Horizons API is open to anyone, if you hammer it enough they may rate limit you, but I don't believe they have limits. As far as I am aware they don't have any API keys or usernames. See: https://ssd-api.jpl.nasa.gov/doc/horizons.html