Editorial: Houston, we have a litter problem

The change in the orientation and orbit of the 17-cm glass-sphere Russian nano-satellite BLITS that was noticed in early February was caused by a January 22 collision with a piece of China’s Feng Yun 1C weather satellite; Feng Yun 1C was intentionally blown up in the 2007 anti-satellite weapon test by China. That irresponsible act led to an overnight increase in the amount of space debris: pieces larger than one centimetre went up by 40,000, and the number of fragments larger than one millimetre by about two million. The number of trackable objects shot up by 25 per cent. Worse, the break-up happened at an altitude of about 860 km, which is heavily populated by satellites. Due to the “low density” of the atmosphere at this altitude, the junk generated will pose a threat to satellites for a long time. The 2008 American experiment when the USA-193 satellite was destroyed by a missile did not create much long-lasting debris. Due to the low altitude (250 km) of break-up, most of the fragments were subjected to air drag and eventually burnt up when they re-entered the Earth’s atmosphere. Aside from these two adventures, the majority of man-made litter larger than 10 cm is from in-orbit explosions. Objects of this size can generate catastrophic events — even a centimetre-long fragment can disable a spacecraft. There are about 600,000 objects in space larger than one centimetre and about 300 million larger than one millimetre.

Nearly 5,000 launches have taken place till date, and nearly half of the catalogued fragments in space are from man-made objects. According to the European Space Agency, doubling the number of objects in space will result in a four-fold increase in collision risk. As the number of launches keeps rising, the possibility of collisions — between two satellites, and between satellites and fragments — producing more debris is increasing. In 2009, the collision of Cosmos 2251, a defunct Russian military satellite, and the American satellite Iridium resulted in 1,700 pieces. As the Kessler syndrome postulates, crashes would first be seen between fragments and larger objects like satellites and would eventually be between two fragments. Crashes will continue till the debris becomes very small. This does not augur well for space science. Expensive manoeuvring of satellites is currently the only way to avoid crashes. But this is possible only in the case of catalogued pieces. Hence it is imperative for space-faring nations to undertake debris-mitigation measures. One of them is to reduce the orbital altitude of dying spacecraft and allow the Earth’s atmospheric drag to pull them into the atmosphere. Objects that re-enter the atmosphere break up at 84-72 km altitude and most of them get burnt up.

Published in The Hindu on April 4, 2013