The space shuttle consists of two solid rocket boosters, an external fuel tank and an orbiter. The two solid rocket boosters are critical for launch, while the external fuel tank carries fuel for the launch and the orbiter carries astronauts and payload.
The solid rocket boosters provide most of the main force required to lift the space shuttle off the launch pad. They also support the weight of the space shuttle orbiter and the fuel tank on the launch pad. Once ignited, the rocket boosters cannot be shut down; therefore, they are the last components activated at launch. The orbiter has three main engines located in the back of the fuselage. They provide the remainder of the thrust needed to lift the shuttle off the launch pad and into orbit. According to the University of Oregon, the solid rocket boosters provide 71 percent of the thrust, whereas the main engines on the orbiter provide the remaining 29 percent.The external fuel tank consists of aluminum and aluminum composite materials, and it has two separate tanks inside. One of the tanks, called the forward tank, is for oxygen, while the adjacent tank, called the aft tank, is used for hydrogen. Fluid flows from each tank through a 17-inch diameter feed line that leads into the shuttle's main engines.