OREKIT (ORbits Extrapolation KIT) is a low level space dynamics Java library. It provides basic elements (such as orbits, dates, attitude, and frames) and various algorithms to handle them (such as conversions, analytical and numerical propagation, and pointing).

Release Notes: The most noteworthy new features are the addition of thread safety for many parts while still preserving caching for performance even in multi-threaded environments, the inclusion of the DSST semi-analytical propagator together with the new unified propagators architecture, support for IERS 2010 conventions, Jacobians availability for all force models, and greatly improved performance and ability for the gravity fields force model. Users are advised to upgrade to this version, which depends on Apache Commons Math 3.2, despite several incompatibilities with respect to previous 5.x versions

orekit – Freecode