This paper presents a methodology for validating MathWorks Simscape as a high-fidelity digital twin for aerospace control system development. A physics-based model of a reusable launch vehicle (RLV) is built with nonlinear effects such as variable mass, actuator limits, and environmental disturb-ances. Using a classical Proportional-Integral-Derivative (PID) controller as a transparent benchmark, the study focus-es on assessing physical fidelity rather than introducing new control methods. Validation compares simulated and expected dynamics, including disturbance rejection, mass-depletion ef-fects, and coupled six-degree-of-freedom responses. Results show Simscape matches the benchmark within 5–8% across the flight envelope, confirming its suitability for advanced Model-Based Design and potential Hardware-in-the-Loop (HIL) workflows. The PID-based framework provides a scal-able, cost-effective alternative to hardware-based verification.