The Space Dweller was first introduced by Rolex on the Japanese market in 1963, just after a visit to Japan by the astronauts of Project Mercury, the United States’ first man-in-space program and the watch was made to honor these men, who were (at that time) seen as the ultimate explorers.
The Space Dweller is essentially identical to the popular 1016 Rolex Explorer, the only difference being the “Space Dweller” branding and the watch was only produced as a test. If the watch was a commercial success, Rolex would then go ahead and re-brand the Explorer as the Space-Dweller for the Japanese market. It was, however, not a success and very few of the Space Dwellers ever made.
They are therefore extremely rare and when they do surface they can expect to sell at auction for $30,000-$40,000, which is not bad for what is essentially a re-badged Rolex Explorer.