Mounted on either side of the space shuttle's external fuel tank are a pair of giant rockets with a single, two-minute purpose: to get the shuttle off the launch pad. The rockets are called the shuttle's solid rocket boosters (SRBs) because they contain solid, as opposed to liquid, propellant. Each booster has a thrust of about 3.3 million pounds of force at launch, enough power to propel the shuttle, its external fuel tank, the boosters themselves, and the shuttle's cargo and crew into the air.

The first two minutes of flight when the boosters are burning are generally considered the most dangerous part of the shuttle launch, with the fewest survivable options should anything go wrong.

The boosters ignite 6.6 seconds after the shuttle's main engines start. If the shuttle engines are performing properly, computer commands are automatically relayed to ignite the boosters and fire explosives...