Comet-chasing spacecraft about to meet its quarry

European scientists were preparing for a historic rendezvous on Wednesday between a comet and a space probe, the climax of a 10-year chase over 6 billion kilometers of the solar system.

The scout spacecraft Rosetta is on track for a meeting with Comet 67P/Churyumov-Gerasimenko in deep space, when it will become the first envoy of mankind to orbit one of the enigmatic space wanderers.

If all goes well, the craft will carry out the first landing on a comet in November. Rosetta will send a robot chemistry lab to the surface to explore a theory that comets hold the key to understanding how our star system formed.

"After completing a complex series of nine orbital maneuvers since the end of hibernation on Jan 20, Rosetta is finally in position to rendezvous with the comet," the European Space Agency said on Tuesday.

Orbital entry will be triggered by small firings of Rosetta's thrusters, lasting just six minutes 26 seconds on Wednesday, it said.

"This burn will tip Rosetta into the first leg of a series of three-legged triangular paths about the comet," it said.

Top officials from the ESA will be at mission control in Darmstadt, Germany, waiting for signals to be received by ground monitoring stations of the start and stop of the crucial final operation, 22 minutes after they occur.

The "pyramidal" orbits will put the craft at a height of about 100 km above the comet, said Sylvain Lodiot, Rosetta's flight operations manager. Each leg of the triangle will be around 100 km and take Rosetta between three and four days to complete.

The arrival will mark a key moment of the boldest project ever undertaken by the ESAa 1.3-billion-euro ($1.76-billion) investigation into one the solar system's mysteries.