Posts Tagged ‘space junk’

A garbage disposal system for space junk

January 17, 2014

NASA keeps track of all the debris in orbit. About 13,000 known objects are bigger than 10 centimeters in diameter and there are more than 100,000 pieces of orbital debris between 1 cm and 10 cm. Pieces smaller than 1 cm number in the tens of millions. All pieces of debris larger than 10 cm are carefully tracked using radar and telescopes.

Many schemes have been proposed for trying to get rid of space debris orbiting the Earth. The schemes have ranged from space harpoons, clouds of of ballistic gas, housekeeping, robotic satellites and laser cannon. The Japanese have a plan for an electrodynamic tether to be attached to the debris by a robot arm. the tether then generates an electric field as it orbits around the Earth and the magnetic field then encourages the debris to drop into lower orbits and eventually burn up. A tether is going to be sent up into space at the end of February for a trial.

Electrodynamic tether

SpaceDaily: Researchers at The Japan Aerospace Exploration Agency (JAXA) have developed what they called an electrodynamic tether made from thin wires of stainless steel and aluminium.

The idea is that one end of the strip will be attached to one of the thousands of dead satellites or bits of rocket that are jamming up space and endangering working equipment.

The electricity generated by the tether as it swings through the Earth’s magnetic field is expected to have a slowing effect on the space junk, which should, scientists say, pull it into a lower and lower orbit.

Eventually the detritus will enter the Earth’s atmosphere, burning up harmlessly long before it has chance to crash to the planet’s surface.

“The experiment is specifically designed to contribute to developing a space debris cleaning method,” said Masahiro Nohmi, associate professor at Kagawa University, who is working with JAXA on the project, told AFP. Nohmi said a satellite developed by the university is expected to be launched into space on February 28, with the tether aboard.

“We have two main objectives in the trial next month,” he said. “First, to extend a 300-metre (1,000-foot) tether in orbit and secondly to observe the transfer of electricity.” The actual reeling in of orbiting rubbish will be the objective of future experiments, he said. A spokesman for JAXA said the agency also plans to conduct its own trial on a tether in 2015.

More than 20,000 bits of cast off equipment, including old satellites, pieces of rocket and other fragments are uselessly orbiting the Earth in a band 800-1,400 kilometres (500-900 miles) from the surface of the planet at terrific speed. 

JAXA write:

If we are able to calculate the motion of debris, we can attach a propulsion system for removal. As the propulsion system, we have envisioned an “electrodynamic tether”, which is extremely efficient because it does not require fuel. The end of an electrically conductive cord (tether) is attached to the debris, transferring it to a lower orbit through the Lorentz force generated by the interference between Earth’s magnetic field and the current flowing through the tether, causing it to re-enter the atmosphere. Two methods are being considered for attaching the tether. One is a method of using a robot arm, for example, to hook the end of the tether into a 1-meter-diameter hole in a payload attachment fitting used as a base for mounting the satellite onto the rocket.  Another is a method where the side of the rocket stage, which is extremely thin for reduced weight, is approached and harpooned by the tether end to attach it. This method is considered to be a safer operation since the tether can be attached from a distance of 10 to 20m.

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