I picked up an old library copy of the illustrated Scribner's edition of Robert Heinlein's Space Cadet and am having fun reading it and pondering the seemingly artless and unresolved juxtaposition of the 1940's-sexist first section of the book with the final section involving the matriarchal Venerian society. But I have a much simpler sci-fi trivia question to ask here.
What is the meaning of the name of the ship that is called P.R.S. Aes Triplex? I checked with my medievalist wife, and she told me "aes" was pronounced like English "ace," then looked up the word and found that it meant "bronze," or some related meaning involving bronze coins or payments. So "triple bronze?" Huh? I'm guessing that "triplex" somehow relates to the three planets with native intelligent life: Venus, Earth, and Mars.