Scientists sounded the alarm yesterday over the problems posed to space missions from orbital junk – the accumulating debris from mankind’s six-decade exploration of the cosmos.
In less than a quarter of a century, the number of orbiting fragments large enough to destroy a spacecraft has more than doubled, a conference in Germany heard.
And the estimated tally of tiny objects – which can harm or degrade spacecraft and satellites in the event of a collision and are hard to track – is now around 150 million.
Scientists pointed to two events that had badly worsened the problem of space junk. The first was in February 2009, when an Iridium telecoms satellite and Kosmos-2251, a Russian military satellite, accidentally collided.The second was in January 2007, when China tested an anti-satellite weapon on an old Fengyun weather satellite. Experts also pointed to two sites that have become worryingly cluttered.One is low Earth orbit which is used by satnav satellites, the ISS, China’s manned missions and the Hubble telescope, among others.The other is in geostationary orbit, and is used by communications, weather and surveillance satellites that must maintain a fixed position relative to Earth.
The conference in Darmstadt, whose opening was broadcast online, is the biggest-ever gathering dedicated to space debris.
Experts will spend four days discussing debris and measures to mitigate space litter such as by ‘de-orbiting’ satellites after their working lives.
During the first day, scientists pointed to two events that had badly worsened the problem, creating debris fields that may generate further junk as pieces smash into each other.
The first was in February 2009, when an Iridium telecoms satellite and Kosmos-2251, a Russian military satellite, accidentally collided.
The second was in January 2007, when China tested an anti-satellite weapon on an old Fengyun weather satellite.
Experts also pointed to two once-pristine sites that have become worryingly cluttered since the space age dawned in 1957.
One is low Earth orbit – generally defined as less than 2,000 kilometres (1,200 miles) from Earth – which is used by satnav satellites, the ISS, China’s manned missions and the Hubble telescope, among others.
The other is in geostationary orbit, a coveted zone 35,000 km (22,000 miles) away used by communications, weather and surveillance satellites that must maintain a fixed position relative to Earth.
The trash ranges from fuel tanks and Soviet-era nuclear-powered satellites, dripping sodium and potassium coolant from decrepit hulls, to nuts, bolts and tools dropped by spacewalking astronauts.
The items ironically include a 1.5-metre (five-feet) debris shield that floated off as it was being installed on the ISS on March 30.
Lost in low orbit, the shield will eventually be plucked into Earth’s atmosphere and burn up.
‘We are very much concerned,’ said Rolf Densing, director of operations at the European Space Agency (ESA), pleading for a worldwide effort to tackle the mess.
‘This problem can only be solved globally.’
Travelling at up to 28,000 kilometres (17,500 miles) per hour, even a minute object impacts with enough energy to damage the surface of a satellite or manned spacecraft.
In 1993, monitoring by ground-based radar showed there to be around 8,000 man-made objects in orbit that were larger than 10 centimetres (4.5 inches) across, a size big enough to inflict catastrophic damage, said Holger Krag, in charge of ESA’s space debris office.
With enough warning, satellites can shift position to avoid a collision, but this uses fuel and potentially shortens operational life.
ESA receives a high-risk collision alert every week on average for its 10 satellites in low-Earth orbit, Dr Krag said.
Each has to resort to ‘one or two’ avoidance manoeuvres per year.
‘Today, we find in space roughly 5,000 objects with sizes larger than 1 metre (3.25 feet), roughly 20,000 objects with sizes over 10 centimetres… and 750,000 ‘flying bullets’ of around one centimetre (half an inch),’ he said.
‘For objects larger than one millimetre (0.04 inch), 150 million is our model estimate for that.’
Risks of collision are statistically remote, but rise as litter increases and more satellites are deployed.
The launch of ‘mega-constellations’ of thousands of communication satellites could lead to a rise in collisions and build-up of space junk in Earth’s orbit, scientists have warned. A decrease in the cost of the manufacture of satellites is set to lead to the deployment of hundreds or thousands into space from next year, creating a massive rise in the number of active satellites from the 1,300 currently in use.But Dr Hugh Lewis, senior lecture in aerospace engineering at the University of Southampton, has warned a 200-year computer simulation has shown the creation of a mega-constellation could create a 50 per cent increase in the number of ‘catastrophic collisions’ between satellites.He said this would increase the amount of space junk in orbit leading to the possibility of further collisions and the subsequent impact on the services provided by the satellites.He added: ‘There has been a paradigm shift in the manufacturing of satellites.’The cost of making a single communications satellite usually runs to hundreds of millions of pounds, but mass-produced satellites will potentially be much cheaper.’The constellations that are due to be deployed from next year contain an unprecedented number of satellites – and a constellation launched without much thought will see a significant impact on the space environment because of the increased rate of collisions that might occur.’Dr Lewis’ study, funded by the European Space Agency, has created a series of guidelines to help prevent collisions including decreasing the amount of time spent in low orbit after the end of a mission, making the satellites smaller and more lightweight, adding propulsion systems and deploying missions to remove faulty satellites.
‘The growth in the number of fragments has deviated from the linear trend in the past and has entered into the more feared exponential trend,’ Dr Krag warned.
In a message from the International Space Station, French astronaut Thomas Pesquet said the station was shielded for objects up to 1 cm (0.4 inches) across.
The ISS often has to make manoeuvres to avoid debris, but needs 24 hours’ warning to do this, using on board thrusters, he said.
If there is less time, ‘our crew will have to close all the hatches and enter the safe haven which is our Soyuz spacecraft so that we can depart the ISS in the case of a collision,’ he said. ‘This has happened four times in the history of the ISS programme.’
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