The 200th Ariane space mission is set to blast off from a base in French Guyana later.
As well as being an anniversary flight, it will also be carrying the heaviest cargo ever sent into orbit by the European project.
The Automated Transfer Vehicle will carry supplies to the International Space Station.
An hour after launch and 260 kilometres up in space, the ATV2 will separate from its rocket booster and embark on an orbit at 7.6 kilometres a second.
It will still take it eight days to reach the International Space Station.
The remote link-up involves fitting the ATV2 into a 10 cm wide port on the ISS at a speed of 28,000 kilometres an hour.
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