Cumulative North-South Propellant Mass for Geostationary Platforms: Residual Transport Inside Existing Dead-Bands

Geostationary platforms allocate approximately fifty meters per second annually for north–south station-keeping to counteract lunisolar inclination drift, accumulating over seven hundred meters per second over a fifteen-year design life. Classical budgeting accurately predicts mean secular rates but leaves residual motion after removal of that rate unquantified relative to the inclination and longitude dead-bands already adopted by operators. This paper extracts the thinness ratio Θ(T) and gap-closure timescale τ_gap from existing high-fidelity ensembles to compute a coherence horizon: the interval over which residual transport is expected to remain thin inside the dead-bands. When the coherence horizon comfortably exceeds the design life, the classical annual allocation stands. When residual transport approaches dead-band boundaries, a typically small gap-protection component—a few meters per second per year or less—is added to maintain spectral separation. A representative illustration shows that under nominal lunisolar forcing Θ(15 yr) remains below threshold; however, near resonant surfaces the gap-closure timescale may fall to design-life values, requiring a modest additional allocation that remains a small fraction of the cumulative ~750 m/s classical total. The diagnostics re-use existing station-keeping ensembles, add no new force models, and never replace classical secular-rate calculations. Sensitivity to dead-band width and resonance proximity constitutes the dominant uncertainty. All constructions remain experimental, require parallel classical analysis, and must undergo independent scrutiny before influencing propellant margins. The practical result is an optional, typically small line item that keeps residual-transport risk visible within the multi-year propellant budget for geostationary north–south control.