The Mobile Servicing Center (MSC) of the Space Station Freedom (SSF) consists of two seven-joint manipulator arms mounted on a transporter which can move along the Space Station truss structure. This system will be used in a wide range of activities onboard the SSF: from handling payloads and assisting in orbiter/Space Station docking to performing various maintenance functions. The Systems Engineering Simulator laboratory at Johnson Space Center was tasked with the construction of the first real-time, man-in-the-loop MSC simulator for use in early operational procedures development and manipulator design testing activities. The authors describe in detail the simulator hardware and software designs as well as the development of mathematical models used in simulating the dynamics and control of the kinematically redundant arms of the MSC.>