Proton KM-4 Briz M

N2O4/UDMH propellant rocket stage. New upper stage for Proton, replacing Energia Corporation's Block DM, making Proton an all-Khrunichev launch vehicle. The Khrunichev-built Briz-M upper stage is a derivative of the flight-proven Briz -K stage (as used on the Rokot booster).

The Briz-M consists of a central cylinder and a jettisonable external propellant tank. Propellant carried is dependent on the specific mission requirements and is varied to maximize performance for the mission. The Briz-M is capable of operating, on-orbit, for a minimum of 24-hours and is controlled by a closed loop, triple redundant guidance system that is commandable in flight.