If you are ready to fork out millions of dollars for an unusual vacation then the moon might just be the place.

Space Adventures, a Vienna, Va., firm that has emerged as the world’s first true space-travel agency, is working with Russia’s Space Agency to devise a 17-day trip that includes a stop at the International Space Station before venturing on a trip around the moon and back, officials said.

More precisely, a Space Adventures forecast requested by NASA and Boeing, among others, suggests that 140 private citizens will have reached orbit by 2020, thanks in large part to new, privately funded rockets and capsules set to come online in the latter half of the decade. The tally does not include passengers taking suborbital flights with companies such as Richard Branson’s Virgin Galactic.

“Realistically, having 140 individuals fly by the time 2020 rolls around is a pretty darn big accomplishment,” Christian Science Monitor quoted Eric Anderson, chairman of Space Adventures, as saying.

“If you extrapolate out with the same multiple, you might find that by the 2020s, there might be a couple of thousand or more people flying to orbit,” added Mr. Anderson.

As currently envisioned, the trip would take place in two phases. Passengers would first travel to the International Space Station, where during a 10-day stay they would become acclimated to living in microgravity.

While they stare out on Earth from the station’s new cupola, Russia would launch the additional service module. The tourists and their pilot would return to their Soyuz capsule, leave the station, and rendezvous with the module.

With the extra kick from the upper—stage motor, the trio would travel to the moon in 3—1/2 days, spend what Mr. Anderson calls “some destination time” orbiting the moon, then head back to Earth.

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