Zefiro 23 is a solid-propellant motor built using Filament Winding technology. 7.5 metres tall, it has a diameter of around 2 metres and weighs 26 tonnes, of which 24 tonnes consist of solid propellant. Zefiro 23 is designed to fire 107 seconds after lift-off and to raise Vega from an altitude of 44 Km to 150 Km from Earth in 80 seconds.
This engine passed its first static bench test in mid-2006 and successfully completed its qualifying test on 27 March 2008. Both tests were performed at the Poligono Interforze di Salto di Quirra (Salto di Quirra Interforce firing Range) in Sardinia.