The space shuttle Atlantis seen against the Earth on a previous mission to the International Space Station. Photograph: Nasa/REUTERS
The 135th and final space shuttle mission is due to begin with the launch of Atlantis from Florida at 16:26 BST on Friday. The 12-day mission to the International Space Station carries a crew of four, and the Italian-built Raffaello pressurized container. This is stuffed with more than 7,000kg of supplies and spares, enough to keep the station going for a year if needed.
For the foreseeable future, though, the ISS must rely on Russian Soyuz craft for crew exchanges, and Russian Progress vessels, European ATVs and Japanese HTVs for further logistics. It will be much longer than a year before the US regains its ability to place a man in orbit. Among mass layoffs, considerable uncertainty and protests, Nasa can do little more than hope that private sector enterprise will carry the US back into low Earth orbit and the ISS, while Nasa itself focuses on more distant manned exploration, perhaps to a passing near-Earth asteroid. A series of recent orbital boosts has seen the altitude of the ISS raised by more than 40km to an average of 388km, higher than it has been for eight years.
Its higher orbit means that it suffers less atmospheric drag at a time when climbing solar activity is exciting the outer atmosphere and increasing the rate at which satellites spiral downwards towards reentry. Without timely orbital boosts, the ISS could spiral to its destruction within a year.
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