Space Junk: Scientists fear debris is reaching tipping point
DEPENDING on the version you read, her name was Henny Penny or Chicken Licken and she was the one in the story who sparked fear among the other animals by shouting “The sky is falling!” after an acorn fell on her head.
There were a lot of Henny Pennys running around last month before one of Nasa’s acorns — a six tonne satellite called UARS — re-entered the atmosphere and fell to Earth. The internet was ablaze with the chatter on where the bus-sized metal hulk would land, and the odds of it killing someone. Headlines ranged from the sober (‘Doomed satellite to hit Earth’), to the amusing (‘Duck! Nasa satellite to crash on Earth’), to the downright silly (‘The sky is falling as UARS drops in’).
Nasa worked out that the odds of someone being hit by a chunk of satellite were 1 in 3,200. No one bothered to work out the probability of a space-based story capturing the public’s imagination just in time for World Space Week, which runs from October 4-10.
The good news is that the remains of UARS splashed down somewhere in the Pacific Ocean. The bad news is that another dead satellite is slowly skimming the upper atmosphere and could spiral uncontrollably to Earth some time in October. This time it’s a German space telescope called ROSAT, weighing in at just under 2.5 tonnes.
Unfortunately, the cyber-Henny Pennys have latched onto this news already with one cheeky site claiming ‘German rogue satellite due to hit Earth and kill millions’. The injury risk to Joe Public from ROSAT is as high as 1 in 2,000 because it is a tougher ship than UARS. The European Space Agency’s head of the space debris office, Heiner Klinkrad, warns that the German satellite may be smaller than its US counterpart, but more of it will reach the planet‘s surface. “This is indeed because ROSAT has a large mirror structure that survives high re-entry temperatures,” he says.
This is not the beginning of some kind of satellite retirement period. “Some of the re-entries we see today are a heritage of years with high launch rates, which were a factor of two higher than they are today,” says Klinkrad. “The trend is towards smaller satellites, with more dedicated payloads.” Smaller craft burn up in the atmosphere on a regular basis, perhaps once a month. The public only gets warned about the large ones.
We’ve had crash-landings before, with more dramatic results. In March 2001, the scorched remains of Russia’s space station Mir splashed into the Pacific near Fiji after a controlled descent. In July 1979, Nasa tried to dump its first space station, Skylab, in the sea south of Cape Town but some pieces survived re-entry and landed in Western Australia. The local council there immediately fined the US $400 for littering.
Space agencies have ensured that all post-1990s spacecraft are capable of being guided on re-entry, so there may not be many more out-of-control machines hurtling back to Earth.
The simple truth is that the Earth is being struck by all kinds of debris all the time. While most of it is simply space dust, an estimated 3 to 7 tonnes of rock between 10 grammes and 1 kilogramme in size enter our atmosphere every year. Most of these objects blaze across the night sky as fireballs and, depending on their makeup, some may even make it all the way to the ground. Some meteorites have landed in Ireland, as recently as last month.
However, rogue satellites such as UARS and ROSAT come from a swarm of artificial objects looming above our planet. This is known as space junk and it has become a serious issue in recent years. Like a cloud of tens of millions of tiny flies, the vast majority of manmade debris in orbit is less than 1cm in diameter, including dust, paint flakes and rocket coolant.
There are about 500,000 objects between 1cm and 10cm, and 19,000 objects larger than 10cm. This latter group includes anything from spacewalkers’ gloves and tools to spent booster rockets tens of metres long.
The immediate vicinity of Earth is very quickly becoming polluted with debris to the point where lives could be put in danger. Most satellites, including the International Space Station, are located in Low-Earth Orbit (LEO). This band lies 160km-2,000km above Earth’s surface, far enough away to avoid the full force of gravity but close enough for the outer atmosphere to drag on objects so they will eventually come back down again.
You may wonder what the big deal is with a few flakes of paint floating about in space, but consider the momentum one tiny fleck can build up. In 1983, the space shuttle Challenger was struck by a paint flake which caused damage to one of the windows. It is estimated that the tiny object was travelling at up to 50,000km/h. In 1994, Endeavour suffered a similar incident which left a hole in a window half of its thickness deep. Two other similar strikes on shuttles have occurred.
The shuttles have been scrapped and Nasa will now rely on private companies to get their personnel and equipment into space. But the threat of space junk could worsen to such a scale that all manned missions are deemed too risky. Scientists fear a scenario called the Kessler Syndrome, a cascade effect caused by debris collisions that would leave a fine cloud of objects surrounding Earth.
Entering such a blanket of debris would be like walking through a firing range. Plans of returning to the moon, walking on Mars or even sending unmanned probes to distant worlds could be grounded for decades, even centuries. Furthermore, no new satellites could be launched, leaving our telecommunications networks at the mercy of ageing spacecraft far out in space.
There is a vast array of telescopes trained on the dense cloud of space junk zipping across the sky, each piece a danger to space shipping.
So, when the next dead satellite tumbles out of the sky you can breathe a sigh of relief that another large piece of space junk has been taken out of the debris cloud.
That is, of course, if it doesn’t hit you. In that case you would wreck Lottie Williams’ title of being the only person to have been struck by space debris. The 56-year-old from Oklahoma walking in a park in 1997 when a fragment from a re-entering Nasa rocket headed her way. “We saw a big ball of fire rushing across the sky and a little spark came off of it,” recalls Williams. “I felt a little tap on the back of my left shoulder and I thought someone was just trying to get my attention. I turned around and looked back because you could hear it hit the ground. Originally I thought it was a shooting star. I’m laughing because that’s what I thought I had, I thought I had a piece of a star.”
It was actually a piece of fibreglass fabric from a Delta II rocket. Even Lottie never thought that the sky was falling down.
CONNECT WITH US TODAY
Be the first to know the latest news and updates
