A European spacecraft that made history by touching down on a comet may have failed to anchor itself firmly to the object’s icy surface, scientists have revealed.
European Space Agency mission controllers clapped, cheered and hugged each other after receiving confirmation that the Philae probe had landed.
But celebrations were tempered by the later discovery that the probe’s two harpoons had not fired to fasten the craft down in the ultra-low gravity.
Scientists now think the probe may have bounced after first coming into contact with the surface.
Philae lander manager Stephan Ulamec said: “Maybe today we didn’t just land once; we landed twice. “What we know is we touched down. We had a very clear signal there and we also received data from the lander. That’s the very good news. Not so good news is that the anchoring harpoons apparently did not fire.
“We’re still don’t fully understand what has happened.
“Hopefully we are sitting there in safety in a position slightly different to the original landing and we can start a scientific sequence.”
Despite the mishap, the probe appears to be operating as intended and collecting data. However, there have been gaps in its radio link with the orbiting Rosetta mothership.
The Philae probe landed on comet 67P/Churyumov-Gerasimenko at the end of an epic four billion mile journey through space that began 10 years ago.
A radio signal, confirming the landing was received by scientists just after 4pm. It took almost 30 minutes for the signal to travel the 316 million miles distance to earth.
Mission controllers had to endure a tense wait of almost seven hours as the spider-like craft descended to the surface of the comet, a 2.5 mile-wide rugged lump of ice and dust hurtling through space at around 40,000mph.
For some of the scientists, the event marks the culmination of 20 years work. It is the first time any man-made object has made a controlled landing on a comet.
Officially announcing the landing, flight director Andrea Accomazzo said: “We can’t be happier than we are now. We have definitely confirmed that the lander is on the surface.”
The probe had travelled with its Rosetta mothership on an epic decade-long odyssey which took it across the asteroid belt, a distance of four billion miles.
Success was never certain. The comet is strewn with deep pits, towering cliffs and peaks, craters and boulders — some the size of houses.
The chosen landing site, named Agilka after an island on the Nile in southern Egypt, was considered the least hazardous of several candidates. As it touched down, the two harpoons sprang from the probe to anchor it to the surface in the low gravity. Ice screws on each of Philae’s three legs will also help to keep it grounded.
At an earlier stage, there was a heart-stopping moment when the lander’s active descent system, which uses thrust to prevent the craft bouncing away into space, could not be primed.
Another glitch was fixed in time-honoured tradition — by switching Philae’s computer off and on again.
During the descent, scientists have no control over the probe’s trajectory, relying on automated systems, careful programming and the pull of gravity.
The separation from Rosetta at 9.05am involved a complex manoeuvre in which Rosetta effectively “dive-bombed” the comet to put the lander on target, before veering away.
Philae touched down on the smaller of two lobes which make up the comet, giving it the appearance of a “rubber duck”.
The probe is equipped with cameras, a suite of 10 instruments, and a drill that can bore out samples to a depth of 9in (23cm).
Two Irish companies are playing a central role in the mission. The design, construction and testing of the electrical support system for Rosetta was done by Susan McKenna Lawlor, a professor at NUI Maynooth, who heads Space Technology Ireland, based on the campus.
The system is considered to be ‘mission critical hardware’ as it is required to handle the communications between the spacecraft and the 11 experiments aboard the Lander Philae on the comet’s surface.
Another firm, Captec, based in Malahide, Co Dublin, wrote the software that lets Rosetta communicate with the smaller Philae probe on the surface.
The lander is designed to collect data for two and a half days, but Rosetta will remain with the comet as it flies past the Sun and heats up, approaching as close as 118 million miles.
Scientists hope the €1.3bn mission will yield valuable information about the origin of the Solar System, the Earth, and possibly life.
By Stephen Rogers and John von Radowitz
Laurence O'Rourke, an engineer from Westmeath who was one of two science operations coordinators for the Rosetta mission last night revealed he had already seen data from the lander probe which they managed to attach to the comet.
“After a wait of many years it is so great to have finally separated the lander and to have watched its descent and landing today,” he told the Irish Examiner last night.
“The data is coming in and I’ve seen already two of the teams who have data from the surface. It’s an extraordinary achievement to fly around a comet and even more to land upon it. It’s an amazing experience to be involved in this mission.
“What we’ve seen from the data is that the harpoons did not fire and as such the lander was not able to anchor itself upon touching the surface. “The lander effectively bounced and came to land a second time and this is where the focus now lies — to find out where exactly it has landed and in what orientation.
“What we believe now is that all we have seen points to Philae being the lander that landed twice. But we will confirm this tomorrow.”
Rosetta’s British project scientist Dr Matt Taylor told the BBC: “To see this mountaineering effort, that we’ve descended a lander to the surface of a comet; I can’t put words to it. It’s beautiful. We did a good job. I knew we were going to do it. We’re down there and we’re doing science. We started science with the Rosetta orbiter in May this year. Now the lander is on the surface it will progress through a number of sequences. We’ll be drilling into the surface of the comet, taking samples, sniffing them, tasting them. We’ll also be getting panoramic images. All of this has never been done before.”
ESA director general Jean-Jacques Dordain said: “ESA and its Rosetta mission partners achieved something extraordinary today. Our ambitious Rosetta mission has secured another place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a probe to a comet’s surface.”
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