An Open-Source, extensible spacecraft simulation and modeling (Open-SESSAME) framework was developed with the aim of providing to researchers the ability to quickly test satellite algorithms while allowing them the ability to view and extend the underlying code. The software is distributed under the GPL (General Public License) and the package's extensibility allows users to implement their own components into the libraries, investigate new algorithms, or tie in existing software or hardware components for algorithm and flight component testing. This thesis presents the purpose behind the development of the framework, the software design architecture and implementation, and a roadmap of the future for the software package.