The term Solid Rocket Booster
) can be used generically, to describe any solid-fuelled rocket designed as an early-stage module, or specifically, in which case it refers to the large external booster rockets attached to the sides of the Space Shuttle
external tank during liftoff
From the www.nasa.gov website:
"Two SRBs provide the main thrust to lift the space shuttle off the pad and up to an altitude of about 150,000 feet, or 24
nautical miles (28 statute miles). In addition, the two SRBs carry the entire weight of the external tank and orbiter and
transmit the weight load through their structure to the mobile launcher platform. Each booster has a thrust (sea level) of
approximately 3,300,000 pounds at launch. They are ignited after the three space shuttle main engines' thrust level is
verified. The two SRBs provide 71.4 percent of the thrust at lift- off and during first-stage ascent. Seventy- five seconds
after SRB separation, SRB apogee occurs at an altitude of approximately 220,000 feet, or 35 nautical miles (41 statute
miles). SRB impact occurs in the ocean approximately 122 nautical miles (141 statute miles) downrange."
Some more random facts about them from various sources:
Heck of a ride...