SIGHS of relief all round greeted the touchdown of STS 114, as the latest space-shuttle flight is known to the cognoscenti. In truth, this was the most mollycoddled mission in NASA's history, so if anything serious had gone wrong with it the agency would probably not have emerged intact from the wreckage. Now, although there are still doubts about whether there will ever be an STS 115, the show can go on. And the next act, expected within a few days—or weeks at most—will be the unveiling of detailed plans for a return to the moon.

But NASA has been upstaged. This week, Space Adventures, a firm based in Arlington, Virginia, announced that it is offering a private trip to the moon for two fare-paying passengers. The catch is the fare—the small matter of $100m a seat.

Although it may seem implausible that a tiny company could offer such a trip, Space Adventures has already organised travel to the International Space Station for two fare-paying passengers, and a third is due to fly in October, so its proposals for lunar tourism need to be taken seriously. And the firm is not actually offering a holiday on the moon. That would be impossible with existing spacecraft. Instead, tourists will follow a figure-of-eight path that will take them swooping low over the surface of the far side of the moon, and then back to Earth.

Space Adventures would not, of course, transport the lunar tourists in its own fleet. The hardware and the pilots would, like those for its trips to the space station, be provided respectively by RSC Energia, Russia's leading spacecraft-maker, and by the Russian Space Agency. However, unlike the space-station jaunts, a trip around the moon would not be a mere commercial recapitulation of a type of mission that had already been flown.

Soyuz, Russia's manned spacecraft, is a tried and tested design, but it has never been to the moon. For that to happen, a Soyuz capsule will have to be launched into orbit on one booster rocket, and then dock with a second booster that has been launched from Earth as a separate payload by yet a third booster. The second booster will provide the oomph necessary to get to the moon and back. Alternatively, for the full extraterrestrial experience, the Soyuz might dock with the space station, allowing passengers a few days in Earth orbit before they go on to the moon.

Eric Anderson, the president of Space Adventures, says that one of the things that makes Soyuz suitable for this mission is that during the cold war space race, the Russians were developing a stripped-down version of Soyuz for a trip to the moon. Nevertheless, some extra research and development would be necessary, as well as modifications to the navigation system, and the enlargement of the craft's window. The latter will have the double benefit of giving passengers a better view and allowing high-resolution pictures of the surface of the moon to be taken. Surprisingly, such holiday snaps would be the first close-up, high-res photos of the lunar surface, which would add a gloss of scientific respectability to the whole enterprise.

According to Mr Anderson, the $200m mission fee will cover the cost of a test launch with an unmanned Soyuz, as well as the costs of the modifications. And if somebody stumped up money now, the mission would be ready to fly in five years. The big question is: who would pay $100m? Space Adventures' market research suggests that at least 1,000 people could afford to do so. Whether any of these billionaires are also brave enough to venture into deep space, and to the far side of the moon, remains to be seen.