Europe's comet chaser Rosetta, the story so far

Tuesday 20th January, 2015

We were very fortunate to have as our speaker Dr Matt Taylor who chairs the Rosetta spacecraft's Science Working Team and he came to talk to us about "Europe's comet chaser Rosetta, the story so far". He is a plasma physicist who has spent most of his academic career working on the Cluster II mission, which consists of four identical spacecraft that are even now studying solar activity.

The Rosetta spacecraft together with a washing-machine-sized lander called Philae (attached to its side) launched on an Ariane 5 rocket on 2nd March 2004. Its original launch date in 2003 had been set in order for it to rendezvous with the comet 46P/Wirtanen in 2011. However, that plan was abandoned when the previous launch of an Ariane 5 in late December 2002 failed as the rocket went out of control and had to be destroyed.

A new target was quickly decided, 67P/Churyumov-Gerasimenko, but it would take 10 years for Rosetta to reach the comet via three flybys of Earth and one of Mars as well as 31 months of hibernation. None of the scientists or engineers were happy about having to put the spacecraft to sleep but it was too far from the Sun for its solar panels to give it enough power to stay awake. On its way to the comet it was able to take images of two asteroids — 21 Lutetia and 2867 Steins.

Finally, in January 2014, the command was sent from Earth for Rosetta to wake up and Dr Taylor said that he could not get to sleep that night and ended up returning to the spacecraft control room in the early morning. To the relief of all, Rosetta sent back a signal to Earth confirming its reactivation but on closer approach to the comet when the first images were received the team were surprised by the strange shape of the comet, resembling a toy duck.

The strange shape and its awkward rotation meant that a lot of discussion went into choosing a landing site that would be well enough illuminated, fairly flat and free of boulders. Dr Taylor explained that the way to envisage the rotation was to imagine the duck lying on its right wing and spinning.

The next critical stage of the mission was when the Philae lander was released to coast gently down to the comet. The comet's gravitational field is very weak and so Philae was equipped with a thruster, harpoon and screws on each of its feet to fix it securely to the surface. However, none of these devices worked successfully and the lander actually bounced a number of times and disappeared from Rosetta's view before finally coming to rest in the partial shadow of a steep cliff. This location meant there was a race on for the small lander to finish as many experiments as possible on the surface of the comet before its batteries ran out. At the moment Philae is hibernating but scientists hope that as the comet approaches the Sun its solar panels will gather more energy and it will be able, just like its parent spacecraft, to awaken and re-establish communication.

Meanwhile Rosetta is continuing its own scientific mission and gathering more data about the comet and material jetting off its surface as its surface warms up. The primary objective of the mission is to gather data about the comet's composition in order to understand the origin and evolution of our Solar System.