Tethers Unlimited Inc. is currently developing a system called the Terminator Tether™ that will provide a low-cost, lightweight, and reliable method of removing objects from low-Earth-orbit (LEO) to mitigate the growth of orbital debris.

Summary:
The Terminator Tether™ is a small device that uses electrodynamic tether drag to deorbit a spacecraft. Because it uses passive electromagnetic interactions with the Earth's magnetic field to lower the orbit of the spacecraft, it requires neither propellant nor power. Thus it can achieve autonomous deorbit of a spacecraft with very low mass requirements.

Concept of Operations:
Before the spacecraft is launched, the Terminator Tether™ is bolted onto the satelite. While the satellite is operational, the tether is wound on a spool, and the device is dormant, waking up periodically to check the status of the spacecraft and listen for activation commands. When the Terminator Tether™ receives a command to deorbit the spacecraft, it deploys a 5 kilometer long tether below the spacecraft. This tether interacts with the ionospheric plasma and the geomagnetic field to produce currents running along the tether, and these currents in turn cause forces on the tether that lower the orbit of the tethered spacecraft. Over a period of several weeks or months, the Terminator Tether™ will reduce the orbital altitude of the spacecraft until it vaporizes in the upper atmosphere.

Papers:

• "The Terminator Tether™: A Low-Mass System for End-of-Life Deorbit of LEO Spacecraft," R.L. Forward, R.P. Hoyt, C. Uphoff, Tether Technical Interchange Meeting, Huntsville, AL Sept 10 1997.
• "The Terminator Tether: Autonomous Deorbit of LEO Spacecraft for Space Debris Mitigation", AIAA Paper 00-0329, 38th AIAA Aerospace Sciences Conference January 2000. (Adobe PDF file)