The Zefiro-9 is the Vega-C rocket's third stage, and burns through around 10 tons of solid propellant, according to ESA. Vega-C's fourth stage is known as AVUM+.

If this stage fails, the rocket doesn’t reach the right height or speed. In this case, EOS-09, meant for Earth observation tasks like city planning, agriculture, and national security, was lost.