ANJANA AHUJA - SCIENCE - Rational reasons to worry about space junk

At some point late next year, China’s first space lab will fall to Earth. Most of Tiangong-1, which means “heavenly palace”, will burn up when it re-enters the atmosphere. China’s space agency has said it will issue warnings closer to the time if the defunct 8.5 tonne cosmic château threatens other satellites.

Tiangong-1 is one of an estimated 18,000 tracked man-made objects that fly around the Earth at speeds of 28,000km/h. Only a fraction of them are functional; more than 90 per cent, including expired satellites and discarded boosters, constitute space junk.

Some satellites are shifted to so-called graveyard orbits when they are no longer required; others are out of power and beyond control, destined to circle the Earth like ghostly relics until impact or atmospheric drag alters their course.

Researchers estimate there are a further 700,000 objects of at least 1cm long, too small to be tracked by the Space Surveillance Network but capable of smashing into other objects, including the International Space Station.

The more tumbling junk there is, the greater the chance of collision, which creates further cascades of debris.

Added dangers come from rubbish raining down on Earth: in November the suspected remnant of a Chinese satellite launch crashed down in a jade mine in Myanmar. No injuries were reported.

Next year there will be several independent attempts at tackling space junk. Surrey Space Centre, based at the University of Surrey in the UK, will test its RemoveDEBRIS technology, designed to be a low-cost, extraterrestrial litter-picking service.

One technology under study is essentially a fishing net designed to capture space junk and pull it back towards Earth, allowing it to burn up in the atmosphere. The Surrey mission will also test a “drag sail”, to be attached to larger pieces of junk. The sail will be jolted by solar radiation, pushing the attached object towards Earth, and towards a similar fiery doom.

Japan’s space agency is also prioritising junk. This month it launched a 700- metre “electrodynamic tether” designed to swing through the Earth’s magnetic field. The forces generated by a tether are designed to nudge junk towards Earth where, again, the atmosphere should be able to fry the detritus.

Meanwhile, the European Space Agency has started the Clean Space Initiative, the centrepiece of which is a 2023 mission to capture a derelict satellite and manoeuvre it into the atmosphere to burn up. The ESA owns one of the largest pieces of space rubbish: an old environmental-monitoring satellite called Envisat, the size of a school bus.

Without a clean-up, the past threatens the future. Next year is the 60th anniversary of the dawn of the space age, which began with the Soviet launch of Sputnik I, the first artificial satellite.

Our planet is now encircled by satellites designed for communications, navigation, television broadcasting, weather forecasting, climate monitoring and military purposes. Modern life depends on them. Both Boeing and SpaceX recently applied for permission to launch “mega-constellations” of thousands of satellites in low Earth orbit to provide satellite broadband.

But the old is not making way for the new: fresh satellites fly among the corpses and body parts of their predecessors. Guidelines recommend that satellites in orbits lower than 2,000km (in other words, low Earth orbit) should be deorbited 25 years after they cease operation - but there is a vacuum where space governance should be.

Various agencies - the ESA, Nasa, the US Air Force Space Command, the Federal Aviation Authority and the International Telecommunications Union - are concerned with the problem but there is a lack of legal clarity on liability for damage caused by space debris.

China added to the problem in a 2007 weapons test, shooting a missile into one of its defunct satellites. The target broke into a huge, trackable debris cloud fluttering throughout low Earth orbit, posing a risk to astronauts on the ISS. Nasa’s chief scientist on debris called the anti-satellite test “the most prolific and serious fragmentation in the course of 50 years of space operations”.

Later that year, the UN General Assembly endorsed space debris mitigation guidelines drawn up by its committee on the peaceful uses of outer space. Most national space agencies have signed up to them but compliance remains voluntary.

There is a growing realisation that we are custodians not just of our planet but also of what lies above. That is why space junk must be urgently reframed as a tragedy of the commons. Instead of being a problem for no one, it must become a problem for everyone - or our days as a spacefaring planet may be numbered.

The writer is a science commentator

Copyright The Financial Times Limited 2016