In the area of Ballistic Missile Defense (BMD), target engagements can traverse numerous intercept envelopes with each
incorporating interceptor systems that utilize different hardware, software, and algorithmic implementations. In the area
of BMD Hardware-in-the-Loop (HWIL) simulation, historical implementations have focused on the development of
simulators which recreate a single "one-on-one" missile engagement, tied to a specific BMD operational envelope, with
other, "many-on-many" digital simulation assets developed independently to explore various battle management and
engagement coordination concepts. In developing the student-utilized Auburn University BMD HWIL simulation, a key
requirement is to construct a single six-degree-of-freedom (6-DOF) simulation software application which allows student
investigation, development, and modeling of guidance, control, and mission planning concepts over the entire
progression of BMD intercept envelopes. In addition, the application must also support real-time data path and control
provisions required by the HWIL simulation. This paper first provides an approach for implementing a "many-on-many"
BMD simulation, allowing concurrent, independent simulation of boost, midcourse, and terminal phase
engagements which comprise an aggregate threat scenario. This approach incorporates an object oriented design
philosophy, as well as specific features of the C++ programming language. Secondly the software architecture is
expanded to achieve the time-critical performance necessary to operate the real-time HWIL simulator, as well to allow
external communications with distributed HWIL simulation components.