http://www.abc.net.au/news/2016-12-06/space-junk-why-it-is-coming-back-to-bite-us/7884396
Space junk: How big is the problem and what are we going to do about it?
Few humans have ever stepped foot in space but as a species we’ve already managed to make a mess of Earth’s backyard. Space junk from satellites and rockets is crowding out spacecraft and telecommunication satellites in Earth’s orbit, and putting humans at risk.
It’s a big problem, and getting bigger every day.
We explain just how big the problem is, and what we’re going to do about it.
Collisions are a major source of space junk
Orbits and what you’ll find there
Most space junk comes from orbiting satellites and the rockets that shot them into place. Gradual wear and tear or sudden collisions cause these to disintegrate into tiny fragments that continue to orbit at tens of thousands of kilometres an hour.
In 2007, China tested an anti-satellite missile by shooting it at one its old satellites, adding nearly 3,500 extra fragments in the area between 160 kilometres and 2,000 kilometres above the surface of our planet.
“That was a significant spike in the amount of space junk out there,” said space researcher Professor Russell Boyce of the University of New South Wales, Canberra and the Australian Academy of Science.
And in 2009, a defunct Cosmos satellite crashed into a functioning Iridium communication satellite, adding thousands more pieces of debris.
Even the tiniest bits of space junk can cause damage
At last count there were over 20,000 pieces of space junk larger than a softball, and about 500,000 larger than a marble orbiting Earth.
Scientists say there are many millions more too small to be seen and the number is growing all the time.
Even the tiniest fragments can cause damage — according to NASA flecks of paint led to a number of space shuttle windows having to be replaced.
It has even been suggested that at some stage the sheer number of bits of space junk will cause a “cascade” of collisions and could render an orbit unusable.
Avoiding space junk collisions is easier said than done
NASA regularly monitors what they call “orbital debris” and try to move their spacecraft out of its way or shield against it.
But, believe it or not, it’s easier to predict the pathway of an object en route to Mars than that of an orbiting piece of space junk.
There are all kinds of things that can affect its orbit ranging from weird and wonderful gravitational anomalies to the effects of the Earth’s magnetic field and even light reflected from the planet and the Sun.
It is not surprising then, that predictions of whether two orbiting objects will collide can be wrong.
Take the collision between the Cosmos and Iridium satellites in 2009: “They were supposed to miss by half a kilometre and they didn’t,” Professor Boyce says.
Space junk can hang around for centuries
While satellites are only built to last a decade or so at most, they can hang around for much longer.
Space junk only returns to Earth when it is slowed down enough by the drag of the atmosphere.
Since the atmosphere gets thinner the further out from Earth you get, space junk higher up generally takes longer to come down of its own accord, and some of it will be up there for centuries.
Historically there has been little thought paid to what happens to satellites once they’re shot up into space.
Only now, some governments — notably the French — are insisting any new satellites must be programmed to come down within 25 years so they don’t contribute to the growing space junk problem.
Junk in ‘graveyard orbit’ coming back to haunt
To counter the problem of colliding space junk, the UN Committee on the Peaceful Use of Outer Space has declared that dead rockets and satellites should be parked in a “graveyard orbit” a bit further out than the geostationary orbit used by communications satellites.
The theory was they wouldn’t fall into lower, more congested, orbits — at least not for a very long time. Well that was the theory…
“Already after a decade or two they are drifting back through the geo belt and creating havoc and nightmare for satellite operators,” Professor Boyce says.
Australia could play a key role in space traffic management
The sheer volume of space junk makes reducing it difficult. This has led to research into what’s called “space situational awareness”, which is all about avoiding collisions.
“We have to develop a space traffic management system so we can constantly monitor everything and constantly give updates to satellites to move out of the way of things,” Professor Boyce says.
Because Australia looks out on a large part of space that can’t be seen by other parts of the world, it provides a critical part of the global surveillance network that is needed for this, he said.
The future: space fences, mini-satellite swarms and space tow trucks
Scientists are working on some pretty out-there technologies to complement the space traffic management system of the future. Here are a few ideas:
Space harpoons to fire from one satellite to another to tow it out of the way to a safer orbit; Robotic arms and nets to help remove debris; Better radar-based ‘space fences’ to detect space junk; Networked swarms of autonomous miniaturised satellites to collect data and help manage space traffic. The nifty thing about these is that they would be programmed to get out the way of things so as to not contribute to congestion themselves. But if one of the swarm did get taken out in a collision the rest could continue the job.Meanwhile … watch out for falling space junk!
Even though space junk can stay in orbit for a long time, when it does start to fall back to Earth it usually does so in an uncontrolled way, Professor Boyce says.
Luckily, most objects are small enough to burn up and vaporise as they fall through the atmosphere — but not all.
This is why scientists try to deliberately program larger objects into a deep-dive down through the atmosphere over the ocean.
The problem is our limited understanding of how space junk behaves means even the best-laid plans can go awry, which is why we got bits of SkyLab and the Mir Space Station landing in random places on Earth.
Right now, scientists are trying to figure out how best to deal with the giant Earth observation spacecraft called Envisat that stopped communicating in April 2012.
The 26-metre-long satellite has been described as a “ticking bomb” and is one of the largest space junk threats in low Earth orbit.