Every Extractor Is a Brake: A Relative-Coupling Ledger for Energy Extraction from Planetary and Orbital Motion

Planets, moons and satellites move continuously and store very large amounts of kinetic energy: about 2.6×10^33 J in Earth's orbit around the Sun and 2.1×10^29 J in its spin. It is tempting to treat this motion as a fuel. This paper argues that it is not. Kinetic energy depends on the reference frame, and continuous power needs a coupling to a second system that can exchange momentum. The paper states this as a ledger of six conditions and draws one consequence from it, the braking identity: the power an extractor delivers is removed from the motion it taps, so every extractor is a brake on its reservoir. The identity gives each reservoir a braking price, the rate at which an observable changes per watt extracted. For Earth's spin the price is 0.64 ms of day length per century per terawatt. For a one-tonne satellite at 400 km it is about 7 km of altitude per year per watt. Applied to ocean tides, which slow Earth's spin and push the Moon outward, the ledger closes to about 6% using commonly quoted values; this checks the accounting and the braking price, not tidal physics independently. The same ledger separates wind and ocean waves, whose energy comes from the Sun, from tides, whose energy comes from planetary motion, and classifies gravity assists, electrodynamic tethers and the Jupiter–Io current system as established couplings. A worked example shows that holding a one-tonne satellite at 400 km against drag costs roughly 15 W of orbital power, which a 1 km tether supplies with about 65 mA; a tether in thruster mode replaces propellant with solar power, but it is not itself a source of energy. Finally, the ledger is applied to the disputed claim that a permeable ferrite shell at rest on Earth's surface extracts sub-picowatt power from Earth's rotation. It shows what evidence such a claim still owes: a reaction on the reservoir and a closed energy account. The paper claims no energy from nothing, and it does not claim that the disputed effect is real.