Early Hardware-in-the-Loop (HWIL) simulation is essential to early retirement of space mission development risks. Upcoming NASA missions such as MMS involve complex high Earth orbits making the use of GPS difficult, though NASA has developed GPS receivers capable of performing in these environments. Space GPS simulation needs are typically seen as a niche market, and the resulting solutions, which are often simply adaptations of terrestrial products, can be sub-optimal and at best handle simple, low dynamic LEO missions. Further, space simulation solutions are frequently inflexible and cannot be modified by the end-user. Given the broad but unique needs of HWIL testing involving RF systems, Emergent proposes to develop the Multi-purpose Radio Signal Generation (MRSiG) system to address these needs, which are essential to early risk mitigation. The MRSiG system will provide for easy mission specific customization and generation of multiple waveforms used in ground testing applications and will return the expertise to simulate these complex environments to NASA. MRSiG will accomplish this difficult task by harnessing the latest in open Software Defined Radio (SDR) technologies. Simulation complexity for RF signal generation is moved into software, enabling the emulation of many RF waveforms/protocols including, but not limited to GPS, 802.11, S-Band, WiMAX, etc.