Orbiter Processing Facility
Orbiter Processing Facility (OPF) is a class of hangars where U.S. Space Shuttle orbiters underwent maintenance between flights. They are located west of the Vehicle Assembly Building, where the orbiter was mated with its External Tank and Solid Rocket Boosters before transport to the launch pad. OPF-1 and OPF-2 are connected with a low bay between them, while OPF-3 is across the street. OPF-3 was previously called the Orbiter Maintenance & Refurbishment Facility (OMRF), but was upgraded to a fully functioning OPF. Processing flow. When a Shuttle mission was completed, the orbiter was towed from the Shuttle Landing  Facility to its assigned OPF where it spent several months (typically less than 100 days) being prepared for the next mission. Any remaining payloads from the previous mission were removed and the vehicle was fully inspected, tested, and refurbished. Prior to rollout to the Vehicle Assembly Building, several weeks before scheduled launch, the orbiter was prepared for the next mission by installing mission flight kits, payloads, consumable fluids and gases where possible. Remaining payloads, fuels and fluids were installed on the pad closer to launch day. The last step before rollover to the VAB was weighing the orbiter to determine  its center of gravity. Current status. OPF-1 was closed following "Atlantis"'s rollout on June 29, 2012. OPF-2 is now inactive following "Atlantis"s departure on October 18, 2012. OPF-3 was under lease to Boeing for the manufacture and testing of their CST-100 Starliner spacecraft. On 8 October 2014, NASA confirmed that Boeing X-37B vehicles would be housed at Kennedy Space Center in OPF-1 and 2, hangars previously occupied by the Space Shuttle. Boeing had said the space planes would use OPF-1 in January 2014, and the Air Force had previously said it was considering consolidating X-37B operations, housed at Vandenberg  Air Force Base in California, nearer to their launch site at Cape Canaveral. NASA also stated that the program had completed tests to determine whether the X-37B, one-fourth the size of the Space Shuttle, could land on the former Shuttle runways. NASA furthermore stated that renovations of the two hangars would be completed by the end of 2014; the main doors of OPF-1 were marked with the message "Home of the X-37B" by this point.