Several software packages I have (co-)written may be of use to you. You can find many things at my github site. Here are a few:
Orbit fitting: C software for finding orbital elements and propagating uncertainties for outer-solar-system bodies, as described in Bernstein & Khushalani (2000) is available here (and auxiliary programs for reading Ephemeris files). These depend on some now-unsupported software. A newer C++ version is here, though not yet documented for public use.
Astrometric and photometric solutions: Code to derive maps of photometric and astrometric response of array cameras, and measure stellar positions and proper motions to high precision. Described in these papers.
Reading the DES astrometry:Python code that can read the high-precisions astrometric solutions for the
Dark Energy Survey exposures.