So far, the commercial development of the solar system has been limited to communications satellites in geostationary orbit and imaging satellites in sun-synchronous orbit. There are indications that this is changing, however. The construction of the International Space Station (ISS) in low Earth orbit and the desire on the part of the Russian partner to make money from the surplus third seat in its Soyuz resupply capsules has produced a nascent space tourism industry. The first person to take advantage of this was the American billionaire Dennis Tito, who paid a reported $20 million for a week's trip to the ISS. The second was South African businessman Mark Shuttleworth, the third was scientist Greg Olsen, and others have undergone evaluation and training for possible future flights.

Of course, very few people are willing or able to afford such a trip, but a precedent has been set, and the possibilities have been demonstrated. Unfortunately, space tourism is technology-limited, in that vehicles that would make it sufficiently cheap and safe for less wealthy adventure tourists to visit LEO do not exist. This is no reason to dismiss it, however. There was a time, still fresh in the memory of many alive today, when lunar exploration vehicles and space stations themselves did not exist.

Although orbital tourism might be some way off, suborbital tourism could be closer than we think. On 27 September 2004, Virgin's chief executive Richard Branson announced that he was entering the space tourism business with Virgin Galactic,...