It is the laboratory with the world's highest overheads. Its capital costs are indeed astronomical. But this month America's International Space Station becomes truly international. An unmanned Russian Progress space truck and a Japanese vehicle called Kounotori, or White Stork, are already plugged into the space station: they came to deliver groceries and fuel; they will remain as temporary accommodation; and they will depart as garbage disposal units. They will be joined next week by a European Space Agency robot delivery van called Johannes Kepler, with more than seven tonnes of propellant, supplies and oxygen. Later in February, the space shuttle Discovery and its astronauts will join the party on what will be its last mission. In April, the shuttle Endeavour will deliver the last hardware, then also retire. Atlantis, the remaining shuttle, stands by for a final mission in June.

Thereafter all fuel, food, water, oxygen, household supplies, experimental apparatus and spare parts will be delivered by the other partners, not by Nasa. When the station's lavatories need to be emptied, Moscow, Paris or Tokyo will take care of it. If the station needs to be moved out of danger, then a European or a Russian tractor will do the heavy lifting. If the people on the ISS need to get home, they must board a Russian Soyuz lifeboat. Each shuttle launch costs Nasa $500m. It can no longer afford to run the fleet and will rely on private enterprise to design, test and fly reusable vehicles between Earth and the ISS. It has contracts with two space entrepreneurs, but neither is yet ready to deliver goods or people to a moving target more than 200 miles overhead.

The planet's only living, breathing outpost is $100bn worth of gleaming hardware the size of a football field, a bright travelling star in the night sky; a self-contained but unsustainable little world of its own; an accident waiting to happen and an opportunity waiting to be seized. The station was a dream of the Apollo era, shaped by 1970s perceptions, authorised in the cold war years to challenge Soviet technology, and rescued by President Clinton as a gesture to the new Russian Federation.

To declare that it should never have been built is to miss the point. It has been occupied for more than 10 years: a high-rise apartment in which humans can practise long-duration survival in microgravity; a gymnasium in which there is no up or down; an observation platform beneath which the planet turns every 90 minutes; the limitless universe beyond. Any future journey to the moon, or Mars, will build on lessons learned aboard the ISS. It is the costliest project ever undertaken: the challenge now is to make it truly valuable.