The failed launch of a Vega-C European rocket in French Guiana last December was due to the deterioration of a key engine component that resulted in a rapid loss of boosting power, European Space Agency officials said Friday.

The launching from the Kourou space port would have been the first commercial launch for the Vega-C and presented a new option for European space payloads after numerous delays to the next-generation Ariane 6 rocket and cancelled Russian cooperation over the Ukraine war.

But shortly after lift-off on December 21 with a payload of two observation satellites, the rocket deviated from its programmed trajectory and communications were lost, forcing officials to destroy it over the Atlantic Ocean.

An ESA investigative panel found that pressure in the Zefiro 40 motor, made by Italy's Avio, had started falling during the second stage of lift-off, the commission's co-president Pierre-Yves Tissier told journalists.

At three minutes 27 seconds after the launch, "the rocket's acceleration had fallen almost to zero," he said.

Investigators determined that a nozzle neck supposed to ensure constant combustion pressure in the motor had failed to resist the enormous pressure and temperatures reaching 3,000 degrees Celsius (5,432 degrees Fahrenheit).

Four astronauts entered the International Space Station on Friday after their SpaceX Dragon Crew-6 mission successfully docked, a NASA livestream showed.

The SpaceX Dragon Endeavour spacecraft arrived at the orbiting station at 0640 GMT on Friday, the US space agency said in a statement.

NASA's Stephen Bowen and Warren Hoburg, Russia's Andrey Fedyaev and Sultan al-Neyadi of the United Arab Emirates entered the station about two hours later, the livestream showed.

A SpaceX Falcon 9 rocket carrying the spacecraft had blasted off to the station on Thursday after the launch was scrubbed just minutes before liftoff earlier in the week.

The crew will spend six months on the station, where they will conduct more than 200 science experiments and technology demonstrations, according to SpaceX.

The mission was the first space flight for Neyadi, Hoburg and Fedyaev.