THE CHALLENGE OF THE SPACESHIP by Arthur C. Clarke     1st Paperback Ed., 1961 - Very Good                                          AIR FORCE! by Frank Harvey - 1st Ed., 1959 - Good       Published by Ballantine Books                                                                                                                                                             In these two books, a famed scientist/sf writer and a noted aviation writer discuss the future of space travel (from the perspective of circa 1960).  CHALLENGE has modest cover edge/corner wear and a name stamped on the top edges and inside front cover.  AIR FORCE  has a crack at the spine at page 52 but holding, as well as some wear at spine bottom and near spine, light back cover creasing, modest edge/corner wear and a bookstore stamp.