Space station astronaut Ron Garan removes a faulty air quality sampler from the U. S. Destiny lab on Sunday. The station mass spectrometer was loaded aboard the shuttle Atlantis for return to Earth. Once the failure mode is established, station astronauts will install a replacement. Photo Credit/NASA TV.
With their visit to the International Space Station drawing to a close, the astronauts assigned to NASA's final shuttle mission finished their cargo exchanges on Sunday, placed once troublesome General Purpose Computer 4 back in a systems management mode and attempted without success to take a few hours off.
Raffaello, the 21-foot-long Multi-Purpose Logistics Module (MPLM) that holds must of the supplies launched aboard Atlantis to the station and returning to Earth, will be sealed early Monday and hoisted from its berthing port on the station's U.S. segment Harmony module to the shuttle's cargo bay.
Atlantis commander Chris Ferguson and his three shuttle colleagues will bid station commander Andrey Borisenko and his five U. S., Russian and Japanese crewmates farewell late in the day.
"We are showing you fully complete with MPLM transfer," NASA's Mission Control informed Atlantis mission specialist Sandra Magnus, who supervised what was a 9 1/2 ton internal cargo exchange between Atlantis and the station. "Hats off to you and the crew. You've done an outstanding job."
"It's been challenging," said Magnus late Sunday. "But we've had a great plan."
Though scheduled for several hours of “off duty” on Sunday, most of the intended time off was absorbed by last minute cargo activities.
Atantis docked with the station on July 10. Almost 11,700 pounds of food, spare parts and research gear were launched aboard Raffaello and on the shuttle mid-deck. Just over 7,200 pounds of unneeded equipment and research materials from the station will return to Earth in the logistics module and the mid-deck.
The “late stow” items headed for the mid-deck included chilled medical specimens collected from station crews to assess how the fliers adapt to long periods of weightlessness.
In addition to internal deliveries, the Atlantis crew dropped off an external robotic satellite refueling experiment and collected a failed external thermal control system circulation pump. The pump, which is secured in the shuttle cargo bay next to Raffaello, is slated for a high priority failure analysis once it returns to Earth.
Over a 10-year history, the three European Space Agency furnished MPLMs hauled 50 tons of cargo to the space station They returned another 20 tons to Earth, a capability that will be lost as the shuttle retires.
"Those are some impressive numbers," said Magnus. "The MPLMs have served us well."
Scheduling calls for Atlantis to undock from the station on Tuesday, just before 2:30 a.m., EDT. Ferguson, pilot Doug Hurley, Magnus and mission specialist Rex Walheim will survey the shuttle's heat shielding for damage and check orbiter steering and communications systems.
If all checks out, the STS-135 crew will descend to Earth early Thursday, ending their 13-day mission and NASA's 30 year space shuttle program on a triumphant note. Touchdown at NASA’s Kennedy Space Center is expected at 5:57 a.m., EDT.
The supplies launched aboard Atlantis are intended to sustain six-person crew operations aboard the station through 2012 -- assuming Russia's highly-reliable Progress cargo capsules run on time. That cushion should enable SpaceX and Orbital Sciences Corp., NASA's emerging U.S. commercial re-supply services, to launch their first missions and establish a flight rhythm.
Also Sunday, GPC 4 was reassigned to the shuttle's systems management role. The processor, one of five that oversee the orbiter's critical functions, experienced a still-unexplained hardware failure late Thursday, also while responsible for shuttle systems management. After being re-initialized on Friday and a pair of subsequent test sessions, GPC 4 resumed the systems management function.
GPC 1 was assigned guidance, navigation and control responsibilities. GPC’s 2 and 3 were placed in standby posture, and GPC 5 in backup mode. GPC 3, which failed to activate July 10 because of a switch problem, has functioned satisfactorily since a re-initialization the next day.