The amount of junk orbiting the Earth is growing, as bits of old satellites and other man-made objects remain in space long after they have ceased to be functional. They bring with them an increasing risk that there will be a serious collision with the satellites that we have come to depend on
There are 17,000 man-made objects currently orbiting in the zone closest to the Earth – and that’s just the hardware that is big enough to monitor. But most of it is junk, nothing more than a giant scrap metal yard in the sky. Only seven per cent of these orbiting items are functioning satellites, the rest is debris from old satellites and the remains of rocket engines or propulsion systems left floating in orbit long after their mission was launched. It doesn’t take a genius to work out that there is a growing risk of the satellites we rely on – for everything from weather warning systems to satellite TV – being seriously damaged as a result of a collision with cosmic debris.
Since Sputnik was launched by the Russians in 1957, there have been more than 6,000 successful satellite launches. Twenty-first century life has come to rely, almost unthinkingly, on satellites. We use them for navigation systems, environmental monitoring, military defence systems, credit card authorisation, radio and television broadcasting, and mobile phone calls, to name but a few things. But what goes up doesn’t always come down.
Scientists are becoming increasingly worried about the growing amount of space debris in low Earth orbit. This orbit zone stretches 2,000 km above the earth’s atmosphere and is the most important area for communications and observation satellites. It is also home to the Hubble Space Telescope and the International Space Station, which are equally at risk of taking a direct hit. There are an estimated 20,000 to 30,000 objects in orbit over 10 cm in diameter that can be monitored from Earth – a mixture of man-made items and natural objects like meteoroids – and an almost incalculable number of smaller fragments that are undetectable by surveillance systems but that still pose a significant threat.
Donald J. Kessler, a NASA scientist, predicted in 1978 that at some point there would be so much debris in space that the resulting congestion would produce an uncontrollable and exponential growth in collisions and debris. If the so-called Kessler syndrome becomes a reality, operational satellites in low Earth orbit will almost certainly be damaged and their services disrupted. Some predict that the Kessler effect will mean that we are unable to use satellites in the lower echelons of space at all and that, as a result, drastic changes in the technology we use to communicate globally will have to be made.
Hugh Griffiths, president of the IEEE Aerospace and Electronic Systems Society, says that the problem is a “ticking time bomb”.
“A plot of the number of orbital space objects shows a steady rise since the mid-1960s, with two step changes,” he explains. “In January 2007 a Chinese missile destroyed a Chinese weather satellite in polar orbit, generating over 2,000 pieces of debris of the same order of size as a golf ball, and an estimated 150,000 debris particles. In February 2009 the Iridium 33 satellite collided accidentally with the inactive Kosmos-2251 satellite at a speed of some 42,000 km per hour, generating some 1,000 pieces of debris.”
Pieces of debris that cause damage are often small, but with satellites travelling at around 28,000 km per hour, collisions, even with small objects, can be significant. Scientists compare the smallest pieces of metal to bullets, leaving holes in anything they collide with. The larger objects are constantly monitored. “Detection and tracking of space debris is done by large, high-power radars, of the same sort as are used for ballistic missile defence,” says Griffiths. “This allows a catalogue of debris objects to be maintained so that, for example, any threat to the International Space Station can be identified in advance and suitable precautions taken.”
The first recorded collision of two man-made objects occurred in 1996, when a satellite owned by the French government was struck by a rocket that was also French. The satellite was made by Surrey Satellite Technology in the UK. Doug Liddle, head of science at Surrey Satellite Technology, explains: “Our satellites used to have these big booms on them, which help to point them in the right direction. Half the boom got sliced off by the French rocket! It really was a big problem at the time, but now we’re much better at tracking and providing information to the community. We get reports from a US group called the Joint Space Operations Center when we are potentially going to get hit by anything and that allows us to move if we need to. There’s room for error, but they will predict the probability of an impact, so if you’re going to be within 1,000 metres of being hit they let you know.”
The risk of further collisions is not a big issue for Surrey’s satellites yet, he says, but it is a growing problem. “The difficulty comes about because some satellites have the ability to move and some don’t. If you’ve got a large piece of space junk coming towards you, you need to be able to move to get out of its way.”
The only way to prevent the situation from deteriorating is to perform an almighty clear-up. This throws up the thorny question of just who is responsible for clearing up the debris. Space law has failed to keep up with the rapid development of space exploration over the last 50 years. Although space lawyers might sound like they come straight out of a sci-fi novel – and the dream job for bookish, space-loving children – the field of space law is serious and complex. In the case of the 2009 crash between the USA’s Iridium 33 communications satellite and the defunct Russian Kosmos 2251, there was no binding guidance on who was liable. Should Russia have de-orbited its satellite? Should Iridium have moved? The gap in legislation is one of the biggest problems facing the clean-up effort.
So how will the international community go about this cosmic-scale clean-up? As with all major tidying-up sessions, it’s best to start with the big stuff and then move on to sifting through the smaller items. The larger the item, the more debris it will create if a collision occurs, making more work in the future. The key to getting rid of the clutter is to lower the debris’ orbit so that it eventually re-enters the earth’s atmosphere, burning up as it does so. At least that is the hope. A satellite came down over the Netherlands, Germany and the Czech Republic in 2011, but no fragments were ever found.
An organisation called the Inter-Agency Space Debris Coordination Committee is aiming to take the lead in the clean-up. This international advisory group has been working with each country’s space agency, asking them to act as a regulatory body for any satellite owned by that nation. The idea is that every satellite that’s launched needs to be brought back down safely at the end of its life.
“Historically, people have finished using their satellite and they’ve just left it up there, switched on and still in the same orbit, where it could stay for the next few 100 years,” explains Liddle.
“The plan now is that at the end of life, once you turn your satellite off, it will come down within the next 25 years and it will hopefully burn up in the atmosphere. If you don’t think it will burn up in the atmosphere, you have to try to do a controlled re-entry so it will hit the ocean and not some poor bloke sitting in his flat in London. But not many spacecraft can do a controlled re-entry because you need to have a really hefty propulsion system. Another option that a lot of people are using is to incorporate drag sails and make the surface area as big as possible.”
Although awareness of space junk is growing outside the scientific community, the majority of people who rely on satellites for services like phone or internet money transfer and remote working – essentially modern life – have no idea that the technology upon which they unconsciously rely may not be able to continue in its present format if the issue of cosmic debris isn’t addressed.
Doug Liddle puts the dilemma into a nutshell: “If we don’t find a way to resolve it, we’re going to spend an awful lot more money tracking debris and satellites will constantly have to manoeuvre around it. It’s going to be like crossing a really busy road. Up until now it’s been like a quiet country lane.”
