Space probe on course to reach comet after 10 years

A European spacecraft is due to rendezvous with an icy comet today after an epic 10-year journey across the Solar System.

Launched in March 2004, the Rosetta probe’s odyssey has already taken it four billion miles across the asteroid belt and more than five times the Earth’s distance from the Sun.

It is now closing in on its quarry, comet 67P/Churyumov-Gerasimenko, a lump of ice and dust swinging in a wide circuit round the Sun at around 34,175 mph.

The spacecraft will match the comet’s speed to within walking pace as it “arrives” at a distance of just 62 miles.

In November, Rosetta will deploy a small robotic lander, Philae, which will steer itself to the comet’s surface. Philae will send back images and conduct the first in-situ analysis of a comet’s composition.

For the next 17 months, Rosetta will remain close to 67P/Churyumov-Gerasimenko as it heads towards the Sun and heats up, throwing out increasing amounts of gas and dust.

Together, Rosetta and its lander will conduct the most detailed analysis of a comet that has ever been attempted.

Since early May, controllers at the European Space Agency’s operations centre in Darmstadt, Germany, have been putting Rosetta through a tightly controlled series of manoeuvres.

Repeated burns of the craft’s thrusters were made to slow the craft and position it alongside the comet.

“If any glitches in space or on ground had delayed the recent burns, orbital mechanics dictate that we’d only have had a matter of a few days to fix the problem, re-plan the burn and carry it out, otherwise we would have run the risk of missing the comet,” said Trevor Morley, a flight dynamics specialist at the ESA Space Operations Centre (ESOC).

More challenges lie ahead as the comet becomes increasingly active and its coma — the halo of gas and dust surrounding its nucleus — grows.

ESA orbital mechanics expert Frank Budnik said: “On top of a good physical model of the comet nucleus, we also need a good coma model that tells us the density and velocity of particles being emitted from the comet

“We expect the spacecraft to be affected by the surrounding coma in addition to the comet body’s gravitational pull, and these all play into calculating the orbits and the thruster burns required to keep Rosetta near the comet.”

During its journey, Rosetta has looped around the Sun five times, and picked up speed from three “gravity-assist” swing-bys of Earth and one of Mars.

Information from the mission will help scientists understand the origin of comets, the Solar System, and possibly life. Rosetta is due to reach the comet around 10am, Irish time.