RECYCLING SPACE JUNK

According to Jonathan's Space Report there are about 6600 useless american rockets and satellites in Earth orbit. At least 10,000 objects are larger than 10 centimeters. About 100,000 objects are larger than 1 centimeter. According to a report published in journal Science (J.C. Liou and N. L. Johnson, January 20, 2006, vol. 340-341) the pieces of space junk measuring 10 centimeters or more have the total mass of 5,500 tons. Junk mass in low Earth orbit (up to the altitude of 2000 kilometers) is about 2000 tons. Most of the junk is located between the altitudes of 900 km and 1000 km. Inter-Agency Space Debris Coordination Committee (IADC) has been advocating, without success, to enact international law restricting the pollution. Junk in the geostationary orbit needs just a little nudge to be corralled into one lump, but junk in the unpredictable, low Earth orbits is much more difficult to remove. Most of the low Earth orbit junk are russian objects in nearly polar orbits (inclination greater than 70 angle degrees).

Precession of polar and equatorial orbits is negligible, so these orbits are predictable. Furthermore, electrodynamic tethers work well in polar and nearly polar orbits because they can easily change their orbits to match the junk orbits. To make sure that new low Earth orbit satellites have predictable orbits and are easy to remove, the following restrictions are necessary:
- The new satellites are launched toward South Pole.
- Their orbits are circular and polar.
- Altitude of the new satellite (measured in kilometers) equals its right ascension (measured in angle degrees).

Some satellite makers and owners may complain that these restrictions force them to launch the new satellites into less than optimum orbits. This complaint is justified only if the satellite owner pays for the cleanup of his space junk. I am sure that the reduced cost of the cleanup justifies the restrictions.

Small pieces of junk can be captured in a large net attached to the end of the electrodynamic tether. Large pieces must be prepared for the capture by telerobots which despin the junk and guide it to the tether.

Telerobot grabbing a spinning piece of junk

Space junk can be used in many ways:

1. Radiation shield for new satellites and space stations.
2. Counterweight for orbital slings. Several slings placed in Earth orbit at different altitudes can bring new satellites from low orbit to geostationary orbit.
3. Empty fuel tanks can be transformed into a capture tube or an orbital greenhouse.
4. Junk electrotube is a very cheap version of a versatile and reusable system of space transportation called composite electrotube. A small satellite cuts the external fuel tanks of the Space Shuttle into pieces and welds them together to make a crude pipe. Obsolete satellites are attached to the ends of the pipe. Cargo fitted with magnets rides on the pipe and induces magnetic drag in the pipe.

Space junk 500 km above the Earth

BIBLIOGRAPHY

Joseph Carroll, "Space Transport Developing using Orbital Debris".