Typical MissionAbout 6 sec before liftoff the Shuttle's main engines are ignited. The booster rockets are ignited at T =
0, and the hold-down bolts are released. The Shuttle lifts off about 2.5 sec later. When it clears the gantry, it pitches to fly with the orbiter upside down, because the craft's design puts the thrust vector off center. At T + 2 min 12 sec the boosters burn out and are jettisoned to parachute into the ocean for recovery. The Shuttle continues under the power of the main
engines. Just short of orbital velocity, the engines are shut down (T + 8 min 32 sec) and the tank is jettisoned (T + 8 min 50 sec). The orbiter's orbit-adjust engines act as the third stage that puts the craft into orbit.The Shuttle can carry a variety of cargoes (see space exploration), including Spacelab, the Space Telescope, and satellites. After a mission is concluded, the Shuttle's maneuvering engines are fired as retrorockets. Braked by the atmosphere, the craft slows from 25 times the speed of sound to subsonic speeds before landing.CrewUnlike earlier manned space programs, the Shuttle allows greater specialization of crew members and flights by persons from outside the
astronaut corps. There are two principal types of Shuttle astronauts, pilots and mission specialists. Pilots fly the Shuttle, with a mission commander (a senior astronaut) in the left seat of the cockpit. The mission specialist, in charge of the cargo the Shuttle carries, comes from widely ranging disciplines.