Europe's Rosetta spacecraft has made contact with its robot probe Philae soon after the lander embarked on a descent to a comet, according to ground controllers.
Communications were re-established on schedule more than two hours after Philae set off at 08:35 GMT for a 20km descent from the Rosetta orbiter, its home for the last decade.
"Rosetta is receiving a signal from Philae," Paolo Ferri, mission operations department head, said on Wednesday at the European Space Agency (ESA) control centre in Darmstadt, Germany.
"It's a very important moment."
Philae was placed on a trajectory on Wednesday towards 67P/Churyumov-Gerasimenko, a comet now more than 510 million km from Earth and racing towards the Sun at 18km per second.
The fridge-sized robot lab, carrying 10 scientific instruments, will attempt to land at about 15:30 GMT, with a confirmation signal expected on Earth about half an hour later.
With Philae riding piggyback, Rosetta was launched in 2004 for a 6.5-billion-km space trek that saw it enter the comet's orbit in August this year.
Astrophysicists hope Philae will unlock knowledge about the origins of the Solar System and even life on Earth, which some believe may have started with comets "seeding" the planet with life-giving carbon molecules and water.