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 assembled shuttle is moved to the launch pad atop the crawler transporter, where it is ready for launch.