The legislation in question is the Iran Nonproliferation Act (INA), which came into force in 2000. The orbiting tin can is the International Space Station (ISS), an American-led (and largely American financed) project which also involves Japan, Canada, Brazil, the EU and, most notably, Russia. To keep people on it requires regular servicing trips. In practice, that means visits from America's space shuttles (grounded at the moment) and Russia's Soyuz spacecraft. But after April next year, an agreement that committed Russia to supply the space-station programme with flights on Soyuz will expire. From then on, America's space agency, NASA, will not be able to pay for any more Soyuz flights because of the INA.

The act prevents NASA from buying such flights until the president certifies that the Russian government is demonstrating a �sustained commitment� to prevent the transfer of weapons of mass destruction and missile-delivery systems, and also that neither the Russian Space Agency nor any entity reporting to it has made any such transfers in the previous year. So even if the space agency were as clean as a whistle, Russia's government has to be behaving itself. And it isn't, so there is something of an impasse.

In the absence of the shuttle, visits to the station require two Soyuz vehicles: one docked as an emergency escape pod and one to transport astronauts to and from the station, an arrangement that NASA would not be allowed to benefit from after April 2006. But even if shuttles return to service this year, as is planned, they can only remain docked to the station for a few weeks at a time, which puts a limit on the span of any American stay there.