Before a space shuttle launch, several processing steps occur that are rarely seen by the public. The external tank arrives by barge and is lifted vertically in the VAB. Solid rocket boosters and engines are attached to the external tank. Meanwhile, the shuttle is attached to the external tank in the VAB. A payload is prepared and then moved to the launch pad to be inserted into the shuttle. Finally, the fully assembled shuttle and external tank are moved to the launch pad on a crawler where it is ready for launch.