Static firing of Aerojet SRB used on heavier Atlas V configurations. Once ignited, the booster burns for 90 seconds before burning out. The Atlas V rocket can carry up to 5 of these boosters, as of yet that configuration was only used to launch the Pluto-bound New Horizons spacecraft. Notice the acoustic wave at ignition propagating into the distance and kicking dust up. The booster can be seen moving a bit forward at the moment of ignition due to thrust forward.