Vacuum Resonance Gradients and Structural Coupling in USP Field Theory: Scaling Limits, Casimir Anchors, and External-Media Coupling for Deep-Space Structures

This document investigates whether structured macroscopic objects can couple measurably to a nonzero vacuum resonance floor or to gradients of that floor near massive bodies within USP Field Theory. The analysis is deliberately conservative. It does not propose reactionless propulsion, vacuum thrust, or extraction of free energy from empty space. Instead, it distinguishes three regimes: 1.symmetric free-space vacuum coupling, where net force cancels by symmetry; 2.boundary-confined vacuum coupling, where Casimir-type effects provide an experimental anchor but face severe scaling limits; 3.external-gradient and external-media coupling, where engineered structures may improve interaction with photons, plasma, residual atmosphere, magnetic fields, thermal recoil, tethers, or radiation pressure. The document uses the CMB-derived USP resonance floor: Delta f_min ~ k_B T / h ~ 5.7 × 10^10 Hz as an order-of-magnitude background anchor, while emphasizing that this is not a directly extractable macroscopic thrust frequency. A central result is the “Casimir scaling wall”: vacuum-boundary coupling is measurable under nanometer-scale confinement but becomes negligible at ordinary spacecraft structural scales. Counter-rotating ring stations are therefore treated not as vacuum thrusters, but as angular-momentum reservoirs and attitude-control systems that can maintain asymmetric coupling surfaces relative to real external momentum channels. The paper includes quantitative anchors, parameter tables, ISS-scale force estimates, sensor-resolution requirements, null-test protocols, and a methods appendix for residual-force experiments. The only USP-specific beyond-standard claim is framed as a falsifiable residual: F_residual proportional to grad(Delta f) meaning a geometry-correlated force or torque in a calibrated resonance-gradient environment after all known electromagnetic, thermal, radiation-pressure, plasma, atmospheric, magnetic, and gravitational-gradient effects are subtracted. The framework preserves conservation laws and standard orbital mechanics. Internal oscillatory structures can redistribute angular momentum and orientation, but net translation still requires external momentum exchange.