Post date: Mar 27, 2012 12:39:45 PM
GRAPHICS (EPFL) - At least 16,000 objects larger than 10 centimetres in diameter and hundreds of millions of smaller particles are flying around the Earth at speeds of several kilometres per second, creating a problem for spacecraft, which are at an increasing risk of collision.
The threat posed by space junk to orbiting satellites and spacecraft was highlighted at the weekend when a discarded piece of debris from a Russian rocket passed close to the International Space Station (ISS). According to Swiss-based scientists however, the threats could be removed with a robotic spacecraft they are developing to literally grab debris out of orbit. The team says CleanSpace One will be ready to launch in 2016.
To combat this scourge, the Swiss Space Center at the Ecole Polytechnique Federale de Lausanne (EPFL) has launched CleanSpace One, a project to develop and build the first instalment of a family of satellites designed to clean up space debris.
The mission is to collect a single item, the Swiss Cube satellite sent into Space in 2009 but, if successful, will act as a prototype for larger future missions.
The Cube, Switzerland's first orbiting object, has sides of just 10 centimetres in length and weighs less than a kilogram. It was sent to conduct research into night-glow within the Earth's atmosphere, and to develop technology for future spacecraft. Having completed its mission, it will continue to float in Space until the arrival of CleanSpace One.
Acting as a mother ship, CleanSpace One will be sent to collect the Swiss Cube, despite being barely twice its size. It will contain sensors and cameras to help the team of astronauts and EPFL professors on Earth direct it before its robotic arm grabs Swiss Cube and carries it back towards the Earth's atmosphere where the two satellites will disintegrate upon re-entry.
Dr Jean-Philippe Thiran, Professor of Image Processing at EPFL, is currently helping to develop the program by filming a replica of Swiss Cube in a lab at the university in Lausanne, and monitoring its movement on a computer.
There are difficult technological hurdles to overcome, one being the machine's ability to come within range of an object in space and be close enough to capture it.
"One of the very interesting questions which we have to approach the target is 'what is its position, its speed, its rotation speed, and to do that we will use a video camera on board, and this camera will actually record the target and from this recording we will evaluate the rotation and the speed of the target," Thiran explained.
When it gets within range of its target, which will be travelling at 28,000 km/h at an altitude of 630-750 km, CleanSpace One will grab and stabilise it - a difficult mission at such high speeds, particularly if the satellite is rotating.
"We need to approach, to grab the target and there will be a range of sensors, a certain number of sensors on board. Vision will be one very important one because when we approach, when we are getting very close to the target, the camera will be used to really precise, give a precise position and a rotation of the target and that's exactly at that point that we use the video," said Thiran.
After its launch the clean-up satellite will have to adjust its trajectory in order to match its target's orbital plane. To do this it could use a new kind of ultra-compact motor designed for space applications being developed in EPFL laboratories.
Another hurdle is developing robotic arms that can securely grab the item. Work on this is in its infancy and the EPFL team say it won't be ready to be sent into Space until 2016.
One of the academics working one the project is Claude Nicollier, Professor of Spatial technology. Nicollier has personal experience of encountering 'space junk', as an astronaut who flew on four Space Shuttle missions. On his final mission in 1999 Nicollier, now 67, became the first European Space Agency (ESA) astronaut to participate in a spacewalk.
Nicollier explained how he and his colleagues in the crew dealt with various uncomfortable brushes with debris. "One of these debris that will be coming uncomfortably close to the Space Shuttle, typically a few tens of metres and of course as there's always uncertainty these orbits it could be possibly a collision. In that case we would be asked to do a manoeuvre. It was a very small manoeuvre, we were taking a certain altitude with the orbiter and firing thrusters for a few seconds or maybe one second only, to change a little bit our orbit so that the prediction of our orbit and the orbit of the debris that was going to come close to us was going to give a more comfortable distance at the time of the quote-unquote encounter," he said.
Many objects of space debris are spent rocket stages or satellites that have broken up in orbit. If they collide with a functioning satellite they can cause destroy it. On February 10, 2009 the U.S. satellite Iridium-33 exploded upon impact with the abandoned Russian satellite Cosmos-2251, causing $55 million worth of damage and leaving 2,000 additional pieces of debris in space.
Nicollier insists the problem of space debris is becoming more serious, particularly because collisions themselves generate thousands more fragments, further exacerbating the problem.
"There are a lot of debris which are large enough to do damage and they are not tracked and we want to avoid the proliferation of those smaller debris and of course of all the debris in general but we think that if we remove the large debris we will prevent the generation of many more small debris in the future because of collisions which is a pretty high source of debris."
The financial consequences of these collisions are enormous, particularly for insurance companies involved in the space sector, a sum currently estimated at $20 billion to insure existing satellites. Yet although space junk has been proposed as a serious threat to NASA equipment and personnel, this is currently a university-funded project costing $11 million, which the EFPL space team hopes to raise over the next five years.
Swiss Space Center Director Volker Gass says space agencies need to work together to solve the problem of space debris, and is confident that CleanSpace One will be a success.
"The current plan is to develop a bio-inspired gripping system that sees an enemy, will catch its prey in a compliant way, adapting its tendrils around its shape and size of the object that is not going to be compliant and it's not going to be co-operative. The object then is to hold it fast, to draw it close to the mother ship and then together with the mother ship de-orbit and incinerate in the atmosphere," he said.
NASA is only able to monitor space debris greater than 10 centimetres in diameter, but at such high speeds even a simple paint chip can seriously damage a solar panel or the window on a shuttle. To avoid the largest objects before they get critically close, the International Space Station (ISS) must constantly alter its orbit, although an incident last Saturday (March 24) came too quickly for astronauts to take evasive action.
A discarded piece of debris from a Russian rocket narrowly missed the ISS, forcing six astronauts to seek shelter in escape capsules. NASA insisted the space junk wasn't close enough to be a threat, but could have been dangerous had it struck the station.
With astronauts increasingly perturbed by the growing problem of 'space junk', the space community will be watching with interest when CleanSpace One gets to work.