THE space race between America and the Soviet Union was as much about ideological one-upmanship as extraterrestrial exploration. A new space race to the moon has an even less lofty goal: sightseeing. Two space-tourism companies are planning rival lunar missions that could see private individuals paying to fly to Earth's nearest celestial neighbour.

On June 19th Excalibur Almaz, a space company based on the Isle of Man, a British dependency in the Irish Sea, became the second company—after Space Adventures, an American space-tourism firm—to offer tickets for a commercial moonshot. Both firms are charging $150m a seat, a price that includes months of ground-based training. Neither is offering a descent to the moon's surface—just a lunar fly-by.

Whereas the Americans won the first space race, the Russians are favourites for the rematch. Both Excalibur Almaz and Space Adventures are using Russian-made rockets and spacecraft. Space Adventures plans to re-engineer the veteran Soyuz craft that it has used to shuttle seven space tourists up to the International Space Station (ISS). Excalibur Almaz intends to refit two Almaz space stations that were originally made for the Soviet armed forces.

The space-tourism business is famously long on hype but rather short, so far, on results. And both firms face big engineering challenges, to put it mildly. The easier task probably falls to Space Adventures, whose well-tested Soyuz capsules—which have been flying, in one form or another, since the 1960s—require a beefier communications system, larger portholes (everyone wants a window seat, after all) and a better heat shield for re-entry. A separate booster rocket will be necessary to break the craft out of Earth orbit.

Excalibur Almaz's bulky space stations will need a lot more work to convert into lunar spacecraft. The first step will be to attach engines. The company plans to use ion thrusters, a high-tech propulsion system in which propellant is ejected using an electric field. Such motors are extremely efficient, and can be powered from a station's solar panels. But they generate little thrust, meaning that Excalibur Almaz's mission will take at least six months, compared with just six days for Space Adventures' chemical-powered craft. In fact, the low-energy trajectory planned by Excalibur Almaz will take its crew members farther from the Earth than any other humans have been.

A journey that long would be risky. One danger is from unpredictable and potentially deadly solar flares, giant releases of stellar energy that would bombard the craft with radiation and fry its occupants. To protect its passengers, the company plans to build an internal “storm shelter” that uses the spacecraft's water supplies to absorb radiation.

Neither firm will start refitting its spacecraft, a process expected to take around three years, until it has sold all the seats on its maiden flights (two for Space Adventures, three for Excalibur Almaz). The companies are marketing their lunar missions to the same high-tech entrepreneurs and ultra-rich thrill-seekers who have snapped up tourist visits to the ISS and suborbital joyrides—long planned, but yet to fly—with firms such as Virgin Galactic.

Space Adventures already claims to have sold one ticket. That has led Excalibur Almaz to sweeten its deal by offering equity in the company to its first paying passengers. But filling seats may prove tricky. Not only is the asking price more than seven times the $20m cost of a jaunt to the ISS, it also requires months of demanding physical and psychological training. And even if the engineering can be perfected, it remains to be seen how many daredevil billionaires will be willing to spend months cooped up in a metal tube eating freeze-dried food.