CHENNAI: As radars across the world kept an eye on China’s defunct space observatory that crashed into Earth on April 1, their antennas also received signals on a relatively small piece of an Indian rocket reentering the planet over the Atlantic Ocean. The junk , from Isro workhorse PSLV ’s fourth stage, weighed about one tonne and had been circling the Earth for nearly six years.

V Adimurthy, advisor to Isro and former Inter-Agency Space Debris Coordination Committee (IADC) chairman, confirmed that the orbital debris re-entered the space atmosphere on April 3 evening.

Astrophysicist Jonathan McDowell of the Harvard Smithsonian for Astrophysics tweeted, “The 1-tonne PS4 rocket stage from @ISRO’s 2012 PSLV C19 launch reentered over the central Atlantic at 1406 UTC Apr 3.”

He was quoted in Space.com, a US-based space news portal, as saying that the debris had been travelling in a circular path around Earth since the launch on April 26, 2012, of RISAT-1, a remote sensing satellite, by PSLV C-19.

The nearly 10-tonne China’s space lab Tiangong-1, launched in September 2011, plummeted to Earth with pieces falling into South Pacific. Most part of the school-bus-sized craft burned up in the Earth’s atmosphere during its uncontrolled reentry. According to an estimate by the European Space Agency, there are about 166 million objects smaller than 1cm, 750,000 objects between 1cm and 10cm and 29,000 objects larger than 10cm in space. Together, they could weigh about 7,500 tonnes. Space faring countries have been tracking space debris through various methods as they pose a danger of colliding with operational satellites or launch vehicles.

Nasa and the space surveillance network of the US Department of Defense alone have catalogued and tracked about 21,000 objects using special ground-based sensors. These are objects as small as two inches in diameter in the circling in the low Earth orbit and about 39 inches in the geosynchronous orbit.

Isro follows a slew of methods to protect its space assets from debris. The space agency is a member of the Inter-Agency Space Debris Coordination Committee, where the agency exchanges information on space debris with 12 other member countries.

The agency also banks on its sophisticated multi-object tracking radar (MOTR), installed in Satish Dhawan Space Centre and has been operational since 2015. “We track debris through the radar for every rocket launch,” an Isro official said.

Officials said the radar can track 10 objects sized 30cmX30cm simultaneously at a distance of 800km and objects 50cmX50cm size at a range of 1,000km.

