Editing Orbiter Processing Facility (section)

== Processing flow ==
[[Image:STSdiscoveryinopf.jpg|thumb|''[[Space Shuttle Discovery|Discovery]]'' inside OPF-3 following the completion of mission [[STS-114]]]]

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 [[Payload (air and space craft)|payload]]s from the previous mission were removed and the vehicle was fully inspected, tested, and refurbished.<ref name=afterlandingpao>{{cite web|title=From Landing to Launch Orbiter Processing|url=http://www-pao.ksc.nasa.gov/kscpao/nasafact/pdf/orbiterprocessing2002.pdf|publisher=NASA Public Affairs Office|url-status=dead|archive-url=https://web.archive.org/web/20110721053142/http://www-pao.ksc.nasa.gov/kscpao/nasafact/pdf/orbiterprocessing2002.pdf|archive-date=2011-07-21}}</ref>

* The orbiter's [[RS-25|main engines]] were purged to remove the moisture that was a by-product of liquid oxygen and liquid hydrogen combustion.  
* payload bay doors were opened and any hazardous payloads were processed for safety
* fuel cell tanks were drained of remaining cryogenic reactants.  The oxygen system was rendered inert with gaseous nitrogen and the hydrogen system with gaseous helium.
* high-pressure gases were vented from the environmental control and life support systems.
* refuse and other waste products including draining of the potable water system were offloaded
* heat shields were removed from the engines and aft access were opened 
* main engines were locked in place and covers installed.
* scaffolding was installed around the orbiters aft to allow technicians to access the main engines
* main engines were removed and transferred to the [[Main Engine Processing Facility]] for checkout and service
* any needed repairs on the orbiter's thermal protection system including the thermal blankets and the silica tiles were completed.<ref name="USA Newsletter">{{cite web|title=Reliable Shuttle Orbiters Need Special Care|url=http://www.unitedspacealliance.com/news/newsletters/issue080/Articles/ReliableShuttleOrbitersNeedSpecialCare.asp|publisher=United Space Alliance|url-status=dead|archive-url=https://web.archive.org/web/20110522111605/http://unitedspacealliance.com/news/newsletters/issue080/Articles/ReliableShuttleOrbitersNeedSpecialCare.asp|archive-date=2011-05-22}}</ref> 
* the [[Orbital Maneuvering System]] and [[Reaction Control System]] pods were possibly removed and transferred to the [[Hypergol Maintenance Facility]] for troubleshooting, repair or other services.
* any modifications to the orbiter were completed in the OPF.
* After all its flights, the orbiter went through "Down Mission Processing."

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.<ref name=afterlandingpao/>