Foundations, NASA’s Helical Engine, and Newton’s Legacy 1. Introduction: The Quest for Reactionless Propulsion Today we embark on an in‐depth exploration of advanced propulsion systems that—at first glance—seem to defy conventional intuition. According to Sir Isaac Newton, every action has an equal and opposite reaction. In his PhilosophiƦ Naturalis Principia Mathematica , Newton established that the momentum of an isolated system must be conserved. Later, Emmy Noether elegantly formalized this idea: every differentiable symmetry of the action of a physical system has a corresponding conservation law. For example, spatial translation symmetry guarantees conservation of linear momentum. Yet here we stand, contemplating systems that propose to generate thrust by only rearranging internal momentum—without expelling mass. How can a vehicle “move” if, by Newton’s and Noether’s words, its center of mass must remain unchanged in the absence of an external force? Today, we analyz...