The launch from the Kourou base in French Guiana is key to Europe's efforts to build up its security autonomy amid the shocks caused by the US-Russia diplomatic rapprochement.

"The whole world is watching us," Arianespace chief executive David Cavailloles told AFP this month.

Ariane 5 was retired in 2023 and Europe has not been able to use Russia's Soyuz rocket for satellite launches since Russia's 2022 invasion of Ukraine.

Ariane 6 underwent a successful test in July last year and is scheduled to carry out five launches this year.

First scheduled in December, the launch was put back until February 26 and then March 3 -- at 1624GMT -- because of problems getting the satellite to the Kourou base, according to Arianespace.

"All launches have risks. Problems can happen with the launcher, with the satellite. We make sure that everything is ready and if it needs a few extra weeks, a few extra months, it is not a problem," said Lionel Suchet, head of France's National Centre for Space Studies (CNES)

Given the military role of the satellite being put into space, strict security precautions are being taken to limit access at the base while three Rafale fighter jets will patrol the surrounding skies.

"The satellite has to be protected. It has special instruments that must not be seen by just anybody," said Catherine Leveau, CNES director of space transport.

The CSO-3 satellite will complete a network of three French military satellites, with the first two launched in 2018 and 2020 by Soyuz.

The satellites "strengthen" France's military autonomy, according to CNES defence consultant Philippe Steininger.

Some of the images taken by CSO-3 will be shared with the German and Belgian militaries that have invested in the satellites.

Sweden also has access to some images in exchange for letting France use its space research centre near the Arctic town of Kiruna.