One day after NASA brought the shuttle Discovery back from low Earth orbit, a private company plans to announce a more audacious venture, a tourist trip around the Moon. Space Adventures, a company based in Arlington, Va., has already sent two tourists into orbit. Today, it is to unveil an agreement with Russian space officials to send two passengers on a voyage lasting 10 to 21 days, depending partly on its itinerary and whether it includes the International Space Station. A roundtrip ticket will cost $100 million. The space-faring tourists will travel with a Russian pilot. They will steer clear...