Electrodynamic tether
Electrodynamic Tether Power Calculator
A long conductive cable trailing through Earth's magnetic field generates electricity, paying for it in orbital kinetic energy. Size the tether; see the trade.
How this model works & what it omits
V×B EMF, simple Ohm's law circuit with plasma contact resistance, J×B drag back-reaction. plasma sheath physics out of scope. first-order trade only.
An electrodynamic tether (EDT) is a long conductor deployed from a satellite in low Earth orbit (LEO): moving through Earth's magnetic field at ~7.6 km/s, it develops a motional electromotive force (EMF) that drives current through a circuit closed by the surrounding plasma. This electrodynamic tether calculator computes that EMF, the circuit current, the electrical power delivered to the load, and the J×B drag the current costs - a first-order Ohm's-law circuit model with plasma contact resistance in the range NASA's ProSEDS, TSS-1R, and NRL TEPCE flew, and Earth's field from a dipole approximation anchored to the IGRF-13 surface value.
An electrodynamic tether (EDT) is a long thin conductor deployed from a host satellite in low Earth orbit. As the tether moves through Earth's magnetic field at orbital velocity (~7.6 km/s at 500 km), the motional EMF Vemf = ∫ (v×B)·dL drives current through the tether. With a hollow cathode at one end and either a bare-tether collector or a second cathode at the other end, the circuit closes through the surrounding plasma, and the system delivers usable electrical power. The current carried by the tether also reacts against the magnetic field, producing a Lorentz force F = I L × B anti-parallel to the orbital velocity. That force is drag: the EDT trades orbital kinetic energy for electrical energy.
The model in this calculator captures the dominant terms. Earth's magnetic field strength is approximated by the surface equatorial dipole value (~30 µT) attenuated as (RE/r)3 with geocentric radius. The tether is treated as a straight conductor with uniform cross-section and material; resistivities come from CRC Handbook 102nd ed. Plasma contact resistance is a tunable lump (default 50 Ω, in the range NASA ProSEDS, TSS-1R, and NRL TEPCE saw). Load matching follows the maximum-power-transfer theorem: at η=0.5 (matched load) the generator delivers maximum power but converts only half the available EMF energy; the rest is dissipated in the tether and plasma resistance. Users can dial η between 0.05 and 0.95 for mission-specific optimisation.
What this tool does not model: plasma sheath behaviour around bare-tether collectors (the OML / orbital-motion-limited regime), current saturation at high tether voltages, 3-axis tether dynamics (libration, skipping-rope modes), thermal limits, micrometeoroid survivability, and tether deployment dynamics. For flight design, defer to NASA-TM 2003-212624 and references therein.
pick a preset, then tweak the conductor or length.
Orbit
dipole field model - equatorial value, no magnetic latitude correction.
Tether
straight conductor; gravity-gradient stabilised along nadir.
Circuit + geometry
alignment is the effective angle between (v×B) and the tether axis.
EDT generator output
v_orbit 7.61 km/s · B 23.9 µT · L 5.00 km
788.5 V
Motional EMF
132.50 Ω
Tether resistance
182.50 Ω
Total circuit R
2.16 A
Current
852 W
Power delivered
852 W
Power dissipated
0.258 N
J×B drag force
13.5 kg
Tether mass
system note
The 0.258 N drag force pulls energy from the host's orbital kinetic energy - that's where the 852 W of electrical output comes from. For a 100 kg reference host, that's roughly 403.43 km of altitude lost per day; scale inversely with your host mass. Order-of-magnitude only.
power transfer peaks near η = 0.5
