Ariane 5 uses a main engine and two lateral solid propellant boosters. These boosters provide 90 percent of the liftoff thrust (600 tonnes each) and operate for two minutes.

All known large solid boosters (such as those of Ariane 5 or the American Space Shuttle, for instance) are subjected to acoustic vibrations because of pressure oscillations which could adversely affect performance and payload. This phenomenon is due to thermal protection rings in the propellant, which generate vortices at a given frequency causing the motor to enter acoustic resonance , somewhat like a flute or an organ pipe.

Numerical simulations and firing tests have given a better understanding of this phenomenon and made it possible to check that there are no problems in real flight.