The first edition of Exploring Space has the letters ABCDEF on page 160. © 1991 by Western Publishing Company, Inc. Illustrations © 1991 Ron Miller. Published by Golden Press, New York, N.Y. No price listed. The ISBN on the back cover is 0-307-24078-9. Listed as a Golden Guide on the cover and the inside front cover.
This title also exists in a large (5 ¼ by 7 ¾ inch) hardcover. The number on the back cover is 0-307-64078-7.
No cover variant or revised Golden Press edition exists that I am aware of. Still in print by St. Martin's Press.