crewmember Jeffrey Williams confirmed steps and final procedures for closeout of the MPLM which will be relocated from the International Space Station to Discoverys payload bay. Transfer of Leonardo to the shuttle payload bay was completed in preparation for Discoverys departure from the International Space Station. Wilson and Nowak used the Canadarm2 to complete the transfer of the module packed with over 4000 pounds of material to return to Earth. Wilson and Nowak also used the shuttle's arm and extension boom to inspect the shuttle's port wing for any signs of micro-meteoroid damage while on-orbit. The other wing and the nose cap were inspected on flight day 12 following undocking. Major discussion on the ground occurred concerning a small leak, an "APU [auxiliary power unit] 1 fuel tank pressure decay", in either a nitrogen or hydrazine tank, in one of the three redundant auxiliary power units which generate hydraulic power for use controlling the flight control surfaces during landing. Ultimately, tests performed after ISS undocking increased confidence in the integrity of the APU to the point where mission controllers decided to use the unit as normal for the re-entry. Space Shuttle Discoverys STS 121 crew undocked from International Space Station after a 9-day stay. Undocking occurred over the Pacific Ocean just north of New Zealand. Mark Kelly flew Discovery to a point above the station before performing the final separation burn. Crew members also used the Canadarm and the orbital boom sensor system to perform final inspections of the starboard wing and shuttle nosecap for any damage that may have been caused by orbital debris while docked with the International Space Station. Troubleshooting of one of the Flash Evaporator Subsystem (FES) (FES PRI B) was carried out. FES A was to be used during reentry but it was desirable to have both functional. This was in addition to the usual extensive checkout of all systems required for reentry ensuring they were functional. Other activities included a long series of live press conferences from orbit, and preparations for landing, which included stowing items on the middeck, fitting the seats in place, and the CDR and Pilot practicing a simulated landing. Discovery received a clean bill of health on the recent heat shield inspections and was given a Go for landing. There were only two very minor deviations from a nominal landing procedure planned: APU 1 was started early, and, due to