Tech/Electrodynamic Tethering
Electromagnetic Tethering / Electrodynamic Tethers (EDTs)
Electrodynamic tethers, also known as EDTs, are long, conducting wires that are deployed from a craft in earths upper atmos. In general, a tether is a long cable (even up to 100 km or more). These tethers interact with the Earth’s magnetic field to generate an electrical current. The current can be used to power systems, change the orbit, or even slow down the reentry into the Earth’s atmos.
For a 20 km tether in low earth orbit (LEO), this voltage would generally fluctuate between 1,500 to 5,300 volts open circuit, depending on the orbital inclination. If a current is allowed to circulate through the tether and a load, substantial power on the order of 15-30 kW can be generated.
With a sufficiently large power supply onboard the craft, the direction of the current can be reversed and the tether becomes a thruster, raising its orbital height. When current flowed through the tether, it pushes against the Earth’s magnetic field to generate drag thrust, demonstrating propulsion. [1] [2] [3]
The Basic Principle
At its most basic level, an EDT works by utilizing the interaction between a conductor and a magnetic field. The Earth’s magnetic field is a powerful and constant source of magnetic energy. By deploying a long, conducting wire and allowing it to interact with the Earth’s magnetic field, an electrical current is generated.
This process is known as electromagnetic induction. When a conductor, such as a wire, is moved through a magnetic field, it generates an electrical current. The strength of the current is directly proportional to the strength of the magnetic field and the velocity of the conductor.
The craft is equipped with a long, conducting wire that is deployed into Earth’s atmos. As the craft moves through the Earth’s magnetic field, an electrical current is generated in the wire. This current can then be used to power craft's systems or to change the craft’s orbit.
Applications
The electrical current generated by the EDT could be used to power onboard instruments, propulsion systems, and communication systems. This would reduce the need for bulky and expensive batteries or solar panels.
In addition, EDTs could be used to change the orbit of a craft. By adjusting the length of the tether and the craft’s speed, the orbit could be raised or lowered. This would be particularly useful for satellites that require a specific orbit for their mission.
Overall, electrodynamic tethers are a promising technology for Earth’s upper atmos exploration and satellite operations. By harnessing the power of the Earth’s magnetic field, EDTs could enable new capabilities and reduce the hazards of debris.[4]
Further Reading
- ntrs.nasa.gov: Electrodynamic tether
- ntrs.nasa.gov: System Engineering Study of Electrodynamic Tether as a Spaceborne Generator and Radiator of Electromagnetic Waves in the ULF/ELF Frequency Band