Picture a spaceship hundreds of times larger than the Apollo moonships, with propulsion provided by controlled hydrogen bombs. Or consider voyages to other stars taking decades or centuries, even at speeds of thousands of miles per second. Mr. Bova discusses in detail interstellar flight and astrophysics, covering some proposals by noted scientists such as huge interstellar "arks" that will take centuries to cross from one planetary system to another, interstellar ramjets that will use the tenuous interstellar gas to reach speeds of over a hundred thousand miles per second, or antimatter rockets that will propel themselves with the most volatile substance in the universe. This is not a "flying saucer" book, but the author does investigate the possible implications of contacts between humans and other races. Higher mathematics is essentially absent from this volume, which won't bother the younger space enthusiast. The only serious deficiencies are the discussion of Einstein's relativity, which is quantitatively inexact, and the absence of a bibliography.