Orekit (ORbit Extrapolation KIT) is a free java library providing basic space dynamics objects and services. It is licensed by CS Systèmes d'Information under the Apache License Version 2.0. A copy of this license is provided in the LICENSE.txt file. The BUILDING.txt file explains how the library can be built from sources. The src/main/java directory contains the library sources. The src/main/resources directory contains the library data. The src/test/java directory contains the tests sources. The src/test/resources directory contains the tests data. The src/tutorials/java directory contains sources for example use of the library. The src/tutorials/resources directory contains example data. The src/design directory contains pieces for a UML model of the library. Orekit relies on the following free software, all released under business friendly free licenses. compile-time/run-time dependency: - Hipparchus from the Hipparchus project https://hipparchus.org/ released under the Apache Software License, version 2 test-time dependency: - JUnit 4 from Erich Gamma and Kent Beck http://www.junit.org/ released under the Common Public License Version 1.0