Notes: - Per Acknowledgment on page iv, "This book is an expansion of a scientific symposium which originally appeared in the pages of Collier's magazine." Book is edited by Cornelius Ryan. - On copyright page, "Copyright 1952 by the Crowell-Collier Publishing Company. Published by The Viking Press in September 1952." - Chesley Bonestell's signature is on cover art. Note that the list of Illustrations on page xi incorrectly credits the interior appearance of the cover art on page 29 to Rolf Klep.