A classical model of the vacuum as a continuum of massless spin carriers is developed and applied to propellantless propulsion. In this framework, a spacecraft imposes a standing electromagnetic wave with a position‑dependent, time‑varying phase gradient. The vacuum responds by generating a compensating spin current, and the reaction to this induced flow produces thrust without expelling propellant. The model reproduces reported asymmetric‑capacitor forces and suggests that analogous effects may arise in magnetic configurations, to be examined in future work. It further indicates that a static phase gradient can reduce effective inertia by forming an inertial bubble that partially decouples the spacecraft interior from external acceleration. These mechanisms point to near‑term applications in CubeSat‑class probes for Earth‑orbit and deep‑space missions. The present work explores their implementation on such platforms while outlining a pathway from laboratory‑scale devices to an inertial warp‑drive concept—not by curving spacetime, but by reshaping inertia through controlled phase gradients or energy‑density gradients.