Since the beginning of human history the expansion of the human race into new environments has inevitably taken a toll on the pioneers. So it has been in our time, when mankind has begun to expand into the solar system. To the four brave and skillful men who have perished in spacecraft, this book is respectfully dedicated: ROGER B. CHAFFEE, VIRGIL I. GRISSOM, VLADIMIR KOMAROV,
EDWARD H. WHITE II