Finally we end with the Space Shuttle Solid Rocket Boosters (SRBs). The SRBs were the most powerful rocket motors ever flown. Each provided a maximum 3,100,000 lb-ft. of thrust. This is roughly double the most powerful single-combustion chamber liquid-propellant rocket engine, the Rocketdyne F-1. With a combined mass of about 2.6 million pounds, the two SRBs comprise over half the mass of the Shuttle stack at liftoff.