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Mechanisms to deal with space debris

l Snagging and Moving Space Junk: This mechanism will seek out satellite debris in a polar orbit at an altitude between 800 and 1,000 kilometres. The European Space Agency is considering several kinds of “capture mechanisms” to pick up the debris, such as nets, harpoons, robotic arms and tentacles.

l Pushing Debris Out of Space:CleanSpace One, a technology demonstration spacecraft, is expected to launch in 2018 from the back of a modified Airbus A300 jumbo jet. The Swiss Space Systems satellite would then meet up with a decommissioned SwissCube nanosatellite to move it out of orbit.

l Using the Power of Electricity:The Japanese Aerospace Exploration Agency proposes to use an electrodynamic tether whose current would slow down the speed of satellites or space debris. This would make it gradually fall closer to Earth, where it will burn up.

l Solar Sail:A British proposal called CubeSail would use the drag of a solar sail to push orbiting space debris down to lower orbits.

The sparkling stars spread across the opaque canvas of the night sky. Since time immemorial, mankind has been intrigued by the universe. It has kindled our imagination and sparked off numerous scientific quests to explore the myriad mysteries that the universe withholds.

Since the Sputnik 1 was launched in October 4, 1957, by the Soviet Union, there have been numerous artificial satellites, which have been successfully launched. The Goddard Space Flight Centre located in the United States of America presently lists around 2,271 satellites orbiting earth.  Only about 1000 of these are active. However, such scientific progress has exposed us to the potential danger of orbital debris.

Space junk

Space debris encompasses both natural (meteoroid) and artificial (man-made) particles. Meteoroids are in orbit about the sun, while most artificial debris is in orbit about the earth. Hence, the latter is more commonly referred to as orbital debris. The National Aeronautics and Space Administration (NASA) of the US had observed in 2013, that more than 500,000 pieces of debris or “space junk” could be tracked as they orbit the earth. They all travel at a speed of up to 17,500 mph, which is fast enough even for a relatively small piece of orbital debris to damage a satellite or a spacecraft. Additionally, the NASA observed that there are more than 20,000 pieces of debris larger than a softball orbiting the earth and about 500,000 pieces of debris of the size of a marble or larger. There are many millions of pieces of debris that are too small to be tracked. Even tiny paint flecks can damage a spacecraft when travelling at these velocities. In fact, a number of space shuttle windows have been replaced because of damage caused by material that was analysed and shown to be paint flecks. According to Nicholas Johnson, Chief Scientist for orbital debris, NASA, “The greatest risk to space missions comes from non-trackable debris.”

The chances of this junk re-entering the earth’s atmosphere is negligible as mostly, they never reach earth with any substantial mass. When these space junk is fired into the earth’s atmosphere, it is broken down by the heat caused by the friction between the air and the debris. However, they pose serious risks to operational satellites and spacecraft in the orbit and those which are being launched. Scientists also opine that they may contribute to ozone layer depletion.

Tracking the debris

It is extremely important to track orbital debris for ensuring hassle-free launches of new satellites. NASA and the US Department of Defence (DoD) perform this task along with other space organisations. DoD’s Space Surveillance Network can track discrete objects as small as 2 inches (5 centimetres) in diameter in low earth orbit and about 1 yard (1 metre) in geosynchronous orbit. Currently, about 15,000 officially catalogued objects are still in orbit. The total number of tracked objects exceeds 21,000. Using special ground-based sensors and inspections of returned satellite surfaces, NASA statistically determines the extent of the population for objects less than 4 inches (10 centimetres) in diameter. Collision risks are divided into three categories depending upon the size of the threat. For objects which are 4 inches (10 centimetres) and larger, conjunction assessments and collision avoidance manoeuvres are effective in countering objects which can be tracked by the Space Surveillance Network. Objects smaller than this are usually are too small to track and too large to shield against. Debris shields can be effective in withstanding impacts of particles smaller than half an inch (1 centimetre).  

NASA and other space research organisations have in place a list of detailed guidelines to avert collisions. Debris avoidance manoeuvres are planned when the probability of collision from a conjunction reaches limits set in the space shuttle and space station flight rules. If the probability of collision is greater than 1 in 100,000, a manoeuvre will be conducted if it will not result in significant impact to mission objectives. If it is greater than 1 in 10,000, a manoeuvre will be conducted unless it will result in additional risk to the crew.

Presently, the issue of space debris is impacting commercial players who have stakes in satellites positioned in the Earth’s orbit.  There is need to periodically manoeuvre the space carats to avert collisions. Researchers have begun modelling a variety of approaches to deal with space junk, including giant mesh tethers, harpoon systems and drag sails that increase the pull on a satellite to push it into earth’s atmosphere more quickly where they burn up. According to   Bill Ailor, a research fellow at The Aerospace Corp, which specialises in tracking space debris, “It’s very easy to get something into orbit and it’s the dickens to get it out.”

Commercial space operations are increasing exponentially and there is an urgent need to devise mechanisms to deal with space debris to ensure unhindered growth of commercial space operations.