100mn+ millimetre-sized space debris a serious threat to astronauts, says NASA Chief Scientist

The word space debris can commonly be interpreted as man-made objects in space that are no longer serving a useful purpose. This could include large and small defunct satellites, spent upper stages of rockets, etc. However, the larger objects are far lesser in number, and it is far easier to track and predict their movement, whereas the real threat to space assets is posed by millions of millimetre-sized space debris, said a top NASA scientist.

"The biggest objects 10cm and larger are tracked by the US Department of Defense, using their global sensor network. Currently, they track about 47,000 big objects in space, 27,000 of them are 10cm and larger. There are many more debris too small to be tracked, but still large enough to threaten human spaceflight and robotic space missions (satellites)" said Dr. Jer Chyi Liou, NASA Chief Scientist for Orbital Debris.

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He was speaking at a space science workshop organised by the Indian Space Research Organisation (ISRO) and Astronautical Society of India (ASI) in India, about Space Situational Awareness and Space Traffic Management. Sharing data about the orbital debris, Dr. Liou said that are 500,000 objects measuring 1cm or larger and over 100 million objects over the size of 1 millimetre.

Pointing out the hazards posed by objects measuring less than a millimetre, he said that even an object as small as 0.4 mm could penetrate some parts of the spacesuit of a spacewalking astronaut and cause serious damage to space missions.

Explaining why space debris of varying sizes is a constant cause of concern, Dr. Liou mentioned that the average impact speed between two orbiting objects in Low Earth orbit (up to 200 km above the earth's surface) is 10km/second. For context, that is ten times the speed of a bullet and any collision at such high impact speeds could prove catastrophic.

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Speaking of the total mass of orbital debris, he said that it had exceeded 9500 metric tonnes and 4000 tonnes of this was in Low Earth Orbit alone. He mentioned that the major man-made events that caused significant fragmentation of space debris were a Chinese Anti-Satellite missile test in 2007, an accidental collision between a Cosmos and an Iridium satellite in 2009 and the Russian Anti-Satellite Missile test in 2021.

He said that orbital debris was not distributed uniformly in space, as Low Earth Orbit (up to 2000 km from the Earth's surface) had the highest concentration, followed by the Geosynchronous orbit (around 36,000 kmabove the earth's surface). This is explained by the highest concentration of satellites operating in low earth orbit and the rapid growth in the number of cube satellites and constellations in the last two decades.

(With inputs from agencies)

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