The Orbital Debris Problem

There are currently over thirteen thousand satellites and other large objects in orbit around the Earth, and there are countless smaller pieces of debris generated by spacecraft explosions and by collisions between satellites. Until recently, it has been standard practice to put a satellite into orbit and leave it there. However, the number of satellites has grown quickly, and as a result, the amount of orbital debris is growing rapidly. Because this debris is travelling at orbital speeds (7-8 km/s!), it poses a significant threat to the space shuttle, the International Space Station, and the many satellites in Earth orbit.

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Satellites and other objects placed in low-Earth orbit will remain in orbit for many years. How long depends upon their perigee altitude, but objects in orbits above about 700 km will stay in orbit for hundreds or even thousands of years!

Recent studies of the interaction of satellite constellations with the space debris environment have concluded that, without debris mitigation measures, "the debris environment cannot sustain the long-term operation of [large constellations but].... could sustain the long term operation of medium sized constellations of up to 100 satellites deployed in orbits associated with the highest collision risk, or alternatively larger constellations of up to 350 satellites deployed in lower collision risk orbits.... provided that the constellations implement strict mitigation measures such as explosion prevention and immediate satellite de-orbiting upon end-of-life and failure. These findings have proven that low Earth orbit is not a limitless resource and must be managed carefully in the future."[1]

In order to prevent old satellites, spent rockets, and the orbital debris that they generate from making low-Earth-orbit unusable, satellite users must begin to provide a means of removing their old satellites and spent rockets from orbit.

Currently, there is no law requiring that old satellites be removed from orbit, but NASA has recently implemented a guideline for NASA satellites, and it is likely that this guideline, or one like it, will become a law.

Conventional Disposal Method: Rockets and Graveyard Orbits
Satellites typically have some means of propulsion for orbit corrections. One method of removing a satellite from orbit would be to carry extra propellant so that the satellite can bring itself down out of orbit. However, this method requires a large mass of propellant, and every kilo of propellant that must be carried up reduces the weight available for revenue-producing transponders. Moreover, this requires that the rocket and satellite guidance systems must be functional after sitting in orbit for ten years or more. Often, this is not the case, and the satellite ends up stuck in its operational orbit. Some organizations are currently planning on boosting their satellites to higher, "graveyard" orbits at the end of their missions. This also requires that the satellite's power, propulsion, and guidance be working at the end of the satellite's mission. Moreover, it doesn't really solve the problem - it just delays it, somewhat like a toxic waste dump. Recent studies have shown that satellites left in a higher graveyard orbit will slowly break apart as micrometeorites hit them, and the smaller fragments will filter back down to lower altitudes [2]. Thus satellites boosted to higher disposal orbits will eventually endanger operational satellites. Moreover, once the old satellites fragment into smaller particles, it will be nearly impossible to clean up the debris. Consequently, it will be much more cost effective in the long run to deal with the problem properly from the start, and deorbit all old spacecraft, rather than leaving them as a problem for our children to deal with.

The Terminator Tether™
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 space debris and keep Low Earth Orbit safe for future generations.

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please contact TUI at information@tethers.com

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