The shuttle Atlantis astronauts finished packing more 2 tons of old equipment and trash from the International Space Station into a cargo hauler on Sunday for the last shuttle ride back to Earth.
The Italian-built storage pod will be loaded into Atlantis' payload bay early on Monday in advance of the shuttle's departure from the station early on Tuesday. The 13-day mission, the last for NASA's 30-year-old space shuttle program, is due to end with a landing at the Kennedy Space Center in Florida at 5:57 a.m. EDT on Thursday.
"This is really the last train out of town," Atlantis commander Chris Ferguson said during an in-flight interview. "I don't think the full magnitude of everything is really going to hit us until after the wheels stop."
Mr. Ferguson and his three crewmates delivered more than 5 tons of food, clothing, equipment and other supplies for the outpost, a $100-billion project of 16 countries that was finished earlier this year after more than a decade of construction 350 kilometres above Earth.
With help from the six-member live-aboard station crew, the astronauts also packed up 2.5 tons of old equipment, foam packaging and other items no longer needed on the station.
The supplies aboard Atlantis are intended to tide over the station until NASA's newly hired cargo delivery firms begin flying next year. NASA, meanwhile, wants to ramp up development of a new capsule-style spacecraft and heavy-lift booster that can ferry people into deep space, beyond the station's orbit where the shuttles cannot fly.
Flights to take crews to the station will be handled exclusively by Russia until U.S. firms develop spaceships capable of orbital spaceflight.
NASA is bolstering efforts by four firms -- Boeing, Space Exploration Technologies, Sierra Nevada Corp, and Blue Origin, a space travel start-up backed by Amazon founder Jeff Bezos -- with technology development contracts worth $269-million.
NASA hopes the new vehicles will be ready to fly in about 2015. Russia charges the United States more than $50-million per person for Soyuz capsule transportation and training.
Atlantis arrived at the station on July 10, becoming the 37th and final shuttle mission to the station. Over the past 30 years, NASA also flew 98 other shuttle missions to deploy satellites and observatories, including the Hubble Space Telescope, and to conduct research and test technologies.
The shuttle proved to be much more complicated and labor-intensive to prepare for flight and not as safe as expected. Two orbiters were lost in accidents, killing 14 astronauts.
The end of the program will hit central Florida, Houston and other shuttle operational hubs hard, with thousands of engineers and technicians due to lose their jobs shortly after Atlantis lands.
"You have to come to terms with the end before you can really put on a new beginning," Mr. Ferguson said. "I think once we can finally get over the fact that the shuttle is gone and its day has come, I believe we'll begin to pick up the pieces and everyone will see that we really do have some vibrant programs out there that we're working on."