Current methods of validating the cyber resiliency of missile defense systems require testing of actual systems, which removes them from operation and subjects them to potentially damaging effects. Cyber ranges can be used as an alternative, but they are limited in scale, costly, time-consuming to configure and have limited capability to model wireless tactical networks and their inherent vulnerabilities. Hence, a secure virtual environment, which uses virtual representations of tactical hardware and the links that connect them, is needed for validating cyber defenses. We propose to develop Secure Environment for Cyber resiliency Evaluation of Missile Defense Systems (SEC-MDS) which will provide a dynamic, scalable, secure virtual environment for testing cyber resiliency. SEC-MDS will be developed as a reconfigurable system which will integrate virtualized missile defense components, actual cyber-attacks, actual cyber defenses, wired and wireless virtual networks, and cyberspace operations on communication networks, into a real-time, synchronized, instrumented synthetic environment. SEC-MDS will provide a virtualized environment in which real cyber-attacks can be injected without compromising actual systems, including cyber-attacks which can impact connectivity, data transfer, data integrity and timing, as well as zero-day attacks. SEC-MDS will record time-stamped attack progression and the effects on weapon system performance for detailed post-experiment analysis. Approved for Public Release | 20-MDA-10398 (2 Mar 20)