Rosetta's grande finale: Space probe is to crash land on comet it has spent two years orbiting in September (but at just 1 mph)
It has spent almost two years orbiting a dusty comet as it races through the solar system hundreds of millions of miles from Earth.
But now the Rosetta spacecraft's 12 year mission to explore the harsh, alien environment of comet 67P/Churyumov-Gerasimenko is to reach a dramatic end.
The £1.2 billion ($1.5 billion) is to crash land on the rocky and icy surface of the comet in a final bit to learn about its alien environment.
It will see Rosetta joining its lander Philae on 67P, which bounced to a rest beneath a cliff face on the surface of the comet in 2014.
Scientists had initially planned to put the spacecraft into a hibernation mode as it moves further and further away from the sun.
But it was feared the spacecraft may not be able to get enough power on its solar panels to ensure it could stay warm enough to survive.
So rather than risking the hibernation, scientists at the European Space Agency have decided to send Rosetta to the comet's surface in a controlled descent.
In its final ours the space probe will beam back high resolution clos up images of the comet along with other last ditch measurements.
Its mission will then end with it impacting on the surface in what is being described as a 'soft landing'.
Scientists say the impact will take place at around 1.1 miles per hour – about half the speed of the landing by the ill-fated Philae lander.
Dr Matt Taylor, Rosetta project scientist at the European Space Agency, said: 'We're trying to squeeze as many observations in as possible before we run out of solar power.
'30 September will mark the end of spacecraft operations, but the beginning of the phase where the full focus of the teams will be on science.
'That is what the Rosetta mission was launched for and we have years of work ahead of us, thoroughly analyzing its data.'
Rosetta spent 10 years travelling to comet 67P, finally arriving in August 2014 after travelling more than four billion miles from Earth, in what was considered to be a remarkable feat of precision space travel.
In November 2014 the Philae lander it had been carrying was launched towards the comets surface.
It did manage to beam back a handful of pictures before its batteries ran out after 60 hours.
Attempts to re-establish contact with the lander were unsuccessful and in February scientists announced they had given up hope of contacting the probe.
Its Rosetta mothership, however, has continued to orbit the comet gathering data that has revealed crucial insights into the structure of the comet.
Among the discoveries made were that the icy comet appears to carry some of the key building blocks of DNA and proteins – the amino acid glycine and the mineral phosphorus.
Now scientists are preparing to issue Rosetta with a series of manoeuvers that will see ti change its trajectory to descend towards the comet's surface.
About 12 hours before impact it will take a final trajectory change at a distance of just 12.4 miles (20km) above the comet's dusty surface.
However, the exact site of the impact has still to be decided.
Sylvian Loidiot, Rosetta spacecraft operations manager at the European Space Agency, said: 'Planning this phase is in fact far more complex than it was for Philae's landing.
'The last six weeks will be particularly challenging as we fly eccentric orbits around the comet -- in many ways this will be even riskier than the final descent itself.
'The closer we get to the comet, the more influence its non-uniform gravity will have, requiring us to have more control on the trajectory, and therefore more manoeuvres - our planning cycles will have to be executed on much shorter timescales.'
Last month, Rosetta entered a 'safe mode' during a fly by just 3 miles (5 km) from the comet as a result of dust confusing the navigation system.
Rosetta recovered, but the mission team cannot rule out this happening again before the planned end of the mission.
Patrick Martin, Rosetta's mission manager at the European Space Agency, said: 'Although we'll do the best job possible to keep Rosetta safe until then, we know from our experience of nearly two years at the comet that things may not go quite as we plan and, as always, we have to be prepared for the unexpected.
'This is the ultimate challenge for our teams and for our spacecraft, and it will be a very fitting way to end the incredible and successful Rosetta mission.'