Solid Rocket Boosters 

The two Solid Rocket Boosters (SRBs) give the Space Shuttle Main Engines (the SSMEs) the extra boost they need to get the Space Shuttle off the ground and into orbit. They provide most of the power and steering for the first stage of ascent. 

Each SRB contains about 500 tonnes of fuel. All this fuel is burned up during the first two minutes of flight. Once the SRBs are empty, they separate from the Orbiter and External Tank (ET) and fall back to Earth where they are recovered for future use. 

You don’t have to be a rocket scientist to realize that the rockets are solid, as opposed to liquid or gas. The solid fuel used by the rockets gives them their name. The SRBs are the largest solid-fuel motors ever flown and the first designed to be reusable.