Orekit is not thread safe
There are quite a few singletons used in Orekit for handling physical
models (UTC-TAI offsets, JPL ephemerides, IERS Earth Orientation
Parameters) that don't always play well with multi-threaded
Multi-threaded applications are increasingly common, either due to specific application needs or due to environments like Web services, application servers or rich client platforms. So Orekit should be thread-safe to allow developing such multi-threaded applications.
(from redmine: issue id 3, created on 2011-01-12, closed on 2011-01-12)