The launch date for the James Webb Space Telescope has been confirmed for December 24 at 9:20 am from Kourou Base (12:20 GMT).
A jewel of complex engineering, JWST is the largest and most powerful telescope ever sent into space.
It was built in the United States under the supervision of the North American Space Agency and houses European (ESA) and Canadian (CSA) instruments.
Its launch from Kourou, where it arrived in October from California, has been delayed twice after minor problems.
NASA and Arianespace want to rule out any risk related to the launch of the device, which was developed over 20 years at a cost of ten billion dollars.
NASA said an overhaul of the launch will take place on December 21, and if everything is ready, the rocket will be moved to the launch site on December 22.
Touted as the successor to the Hubble Telescope, launched in 1990, the JWST is expected to explore with unparalleled precision the entire universe, and its past, from the early ages of the universe to the formation of the first galaxies.
It will be placed in orbit around the Sun, 1.5 million km from Earth.
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