Europe’s new Ariane 6 rocket is reaching its decisive phase of testing, officials said this week. This includes a short and long-duration firing of the rocket’s first stage at European launch facilities in French Guiana, tests that could occur today and about one month from now.

“They are really the decisive moments when we see how the engines operate under full throttle,” the director general of the European Space Agency, Josef Aschbacher, said during a press briefing on Monday.

Aschbacher declined to specify a launch target for the new medium-lift rocket, the development of which began in 2014, and which was originally due to make its debut in 2020. The European Space Agency and the rocket’s prime contractor, ArianeGroup, are now working toward a launch in 2024.