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 and orbiter in the VAB and SPF. The payload is prepared in the PPR and then transported to the launch pad to be inserted into the orbiter. Finally, the shuttle is moved atop the crawler from the VAB to the launch pad where it is ready for launch.