JDMS 1. Introduction High-fidelity, six-degree-of-freedom (6-DoF) simulations play an important part in the development of weapon systems. These so-called constructive simulations are used in technology trade studies, preliminary design, hardware- in-the-loop evaluation, flight testing and training. 1 The first all-digital, constructive simulations were cre- ated by the National Aeronautics and Space Administration (NASA), U.S. Department of Defense (DoD) and industry. In 1966 Litton Industries developed the architecture for a missile simulation in FORTRAN IV that had all of the fea- tures of a full 6-DoF simulation. It was the source of many derivatives by Hughes Aircraft, North American Aviation and Aerospace Corporation. Noteworthy is the U.S. Army Journal of Defense Modeling and Simulation: Applications, Methodology, Technology XX(X) 1–17 © 2011 The Society for Modeling and Simulation International DOI: 10.1177/1548512910395641 dms.sagepub.com Original article U.S. Air Force Research Laboratory, Eglin AFB, FL, USA Corresponding author: Peter H Zipfel, U.S. Air Force Research Laboratory, Eglin AFB, 73 Country Club Road, Shalimar, FL 32579, USA. Email: mastech.zipfel@cox.net CADAC: Multi-use Architecture for Constructive Aerospace Simulations Peter H Zipfel Abstract In today’s network-centric world, aerospace vehicles interact with many objects. They navigate by overhead satellites, synchronize their flight paths with other vehicles, swarm over hostile territory and attack multiple targets. Studying these engagements with high-fidelity constructive simulations has become an important task of modeling and simulation (M&S). The simulation framework Computer Aided Design of Aerospace Concepts (CADAC) has its roots in FORTRAN code that dates back to the 1960s and was used by industry and the U.S. Air Force to simulate aerospace vehicles in all flight environments. To adapt CADAC to the new environment, a complete rewrite was carried out in C++, taking advantage of object-oriented programming techniques. The architecture of CADAC++ is based on the hierarchical structure of inherited classes. The vehicles (aircraft, missiles, satellites or ground targets), inherit the six-degree-of-freedom (6-DoF) equations of motion from the classes ‘Flat6’ or ‘Round6’, conveying either the flat or elliptical Earth model. In turn, these classes inherit the communication structure from the base class ‘Cadac’.The components of the vehicle, e.g., aerodynamics, propulsion and autopilot, are represented by modules, which are member functions of the vehicle class. Communication among the modules occurs by protected module-variable arrays. Every instantiated vehicle object is encapsulated with its methods and data. To communicate between vehicles, data packets are loaded onto a global data bus for recall by other vehicles. Input occurs by ASCII file and output is compatible with CADAC Studio, a plotting and data processing package. CADAC++ is chiefly an engineering tool for refining the components of the primary vehicle and exploring its performance as it interacts (possibly repeatedly instantiated) with the multi-object environment. Its modular structure enables reuse of component models across simulations. In the 10 years of development, CADAC++ based constructive simulations have been built for many types of aerospace vehicles and integrated with mission-level simulations. Keywords aircraft and missile simulations, engagement simulations, high fidelity modeling, constructive simulations, C++ programming language, six degrees of freedom, CADAC, CADAC studio, three-stage booster, dual role missile, self defense missile, hypersonic cruise missile, multi-object programming, run-time polymorphism classes, communication bus. ENDOSIM simulation. a The U.S. Air Force also adopted it to its own needs and named the simulation Computer Aided Design of Aerospace Concepts (CADAC). a. AMTEC Corporation. Endo-atmospheric Non-nuclear Kill Simulation. Report No. TR 1147. Huntsville, AL: U.S. Army Strategic Defense Command, August 1989 (restricted distri- bution).