From the time a Shuttle stops on the runway following a successful mission, it is being prepared for its next flight. Each Orbiter is subjected to a planned sequence of testing, reconfiguration, maintenance and verification to make it ready for the next mission. That process, which is called "The Flow," takes two to three months and involves thousands of tasks.
The Flow begins when the vehicle is towed from the Shuttle Landing Facility runway into one of three bays of the Orbiter Processing Facility (OPF). OPF-1 and OPF-2 consist of two 29,000 square foot high bays, while OPF-3 is across the street. OPF-3 was previously called the Orbiter Maintenance & Refurbishment Facility (OMRF) but has been upgraded to a fully functioning Orbiter Processing Facility. OPF-3 is a 50,000 square foot facility that consists of a high bay, a two-story low bay area and Space Shuttle Main Engine shop.
Once in the OPF, the Orbiter first undergoes procedures to remove residual fuels and explosive ordnance items. The OrbiterΓÇÖs previous mission payloads are removed, and the vehicle is fully inspected, tested and refurbished for its next mission. As it is prepared for the upcoming flight, the Space ShuttleΓÇÖs main engines as well as the avionics, electrical, hydraulic, mechanical and structural systems are serviced. Extensive checkouts are performed to examine and repair the protective tiles on the surface of the vehicle, and the orbital maneuvering system and reaction control system thrusters are tested. These functions require approximately two-thirds of the time between missions.
While the Orbiter is being processed, the external tank that carries the cryogenic propellants for the ShuttleΓÇÖs main engines and the twin Solid Rocket Boosters (SRBs) are installed on a Mobile Launcher Platform (MLP) in the giant Vehicle Assembly Building (VAB).
The VAB is one of the largest buildings in the world. It is more than 500 feet tall, taller than the Statue of Liberty and larger than the Pentagon in cubic meters. Nearly four Empire State Buildings, if disassembled, could fit inside the VAB. Originally built to house the Saturn V rockets during the Apollo era, the VAB was modified to support Space Shuttle operations.
The ΓÇ£build upΓÇ¥ in the VAB begins when integrated SRB segments are transferred from a nearby assembly and checkout facility and then hoisted onto the launcher platform where the segments are mated together to form two complete boosters. Prior to this time, a new external tank ΓÇô the only piece of the Shuttle System not recovered and reused -- is shipped to KSC by barge from Lockheed-MartinΓÇÖs production facilities in Michoud, Mississippi. When the boosters are complete, the ET is maneuvered carefully into place and attached to the ΓÇ£stack.ΓÇ¥
When servicing of the Orbiter is completed in the OPF, the vehicle is towed on its landing gear to the VAB transfer aisle. There a 300-ton crane lifts the Orbiter, shifts it into its vertical launch position and with precise accuracy moves it into position where it is attached to the waiting boosters and tank. At this point, each of the major components has been checked out as an individual unit. Work proceeds to verify the integrity of the Space Shuttle vehicle system as a whole, as the final tasks are completed to make it ready for the launch pad.
While the Space Shuttle reaches speeds as high as 18,000 miles per hour to attain orbital velocity, it travels at the rate of only one mile per hour on the trip to the launch pad aboard a 6 million-pound tracked vehicle called the Crawler Transporter. Each the size of a baseball infield, the two Crawler Transporters at the Kennedy Space Center are the worldΓÇÖs largest tracked vehicles. Each individual shoe in the transporter tracks weighs one ton. In total, the Shuttle stack, launcher platform and crawler transporter weighs 18.5-million pounds.
During the trip to the launch pad, the Orbiter is kept vertical within plus or minus 10 minutes of arc, about the diameter of a basketball. Leveling systems within the crawler keeps the platform level while negotiating the 5 percent grade leading up to the pad surface. The 3-4 mile trip to the launch pads burns about 150 gallons of diesel fuel per mile.
Because of crawlerΓÇÖs weight, the road from the Vehicle Assembly Building to the Launch Pad was specially constructed to handle the tremendous weight of the crawler and its cargo. Seven feet thick and about the same width as an eight-lane highway, the crawlerway is constructed of graded limestone, fill, asphalt sealer and river rock. The trip to the pad takes about 8 hours before the Space Shuttle is firmly in place on the launch pad and a service structure is rotated into place.
