Apollo 15 postal covers incident in the moon landings, the public's fascination with items flown in space increased, as did their value. Although it was not publicly known until September 1972, 15 of the men who entered space as Apollo Program astronauts, before Apollo 15, had agreed with a West German named Horst Eiermann to autograph 500 philatelic items (postcards and blocks of stamps) in exchange for $2,500. This included a member of each mission between Apollo 7 (1968) and Apollo 13 (1970). These items were not taken into space. Covers were prepared by the crews and flown on Apollo 11, Apollo 13 and Apollo
Apollo 21 in orbit. Some people have speculated that tentative plans of an "Apollo 21" might have been made assuming availability of the extra Saturn V that would have left, although by the time NASA resumed planning manned missions using this numbering sequence (defined on April 24, 1967), the dual-Saturn IB plan had been replaced with the single Saturn V. There is no evidence NASA ever planned an eleventh Moon landing mission. Apollo 21 "Apollo 21" is an apocryphal reference to an eleventh manned Moon landing mission of NASA's Apollo program. Apollo contracted for the construction of fifteen Saturn V launch vehicles