Solid rocket booster
The Solid Rocket Boosters (SRBs) are rocket engines on the space shuttle which operate in parallel with the main engines for the first two minutes of flight. They provide the additional thrust needed for the Orbiter to escape the gravitational pull of the Earth. At an altitude of approximately 45 km, the boosters separate from the orbiter/external tank, descend on parachutes, and land in the Atlantic Ocean. They are recovered by ships, returned to land, and refurbished for reuse. The boosters also assist in guiding the entire vehicle during initial ascent. Thrust of both boosters is equal to 5,300,000 lbs.