SOURCE OF ARTICLE: http://www.nasaspaceflight.com/2009/09/live-sts-128-land-california-sts-131-next-discovery/
Currently targeting launch on March 18, 2010, Discovery’s STS-131 mission will deliver supplies to the International Space Station (ISS) via the Multi-Purpose Logistics Module (MPLM) Raffaello and the Light-weight Multipurpose Experiment Support Structure Carrier (LMC).
Initially, Discovery was to begin processing for STS-131 on August 31. However, due to multiple launch date delays due to External Tank foam concern, weather, and a fill and drain valve, Discovery did not launch until August 29.
Should Discovery land in Florida on Friday, processing for STS-131 will begin once initial safing and excess propellant is offloaded from the vehicle in OPF-3 (Orbiter Processing Facility Bay 3).
However, should Discovery land in California, full-up processing for STS-131 will not being until the Orbiter has been flown back across the country — a task that usually takes between nine and ten days to accomplish following a landing at Edwards Air Force Base.
Nevertheless, Discovery’s flow toward STS-131 is longer than the usual OPF flow — ~145-days v. the minimum ~100-days a vehicle can be processed out of the OPF.
During her stay in OPF-3, Discovery will have her #2 APU (Auxiliary Power Unit) — one of three devices (APUs) that provide hydraulic power to the vehicle during launch and entry — replaced due to time and cycle requirements.