Moonstalker — Victor Appleton

SPACE INVADERS!
Tom Swift has developed an ultrapowerful telescopic device that promises to yield dramatic new insight into the deepest mysteries of the universe. But his first discovery is no more than two hundred miles up, and it's a shocker. A tiny cube of polished granite is orbiting the earth, and on its side Tom spots a message -- in a language no one has ever encountered before!

Tom's infrared photo of the object convinces a friend at NASA to use an all-new Swift-enhanced space shuttle to retrieve the mystery stone, but the flight ultimately leads Tom to the surface of the moon. A force of unknown origin, controlled by a hidden intelligence, has lured the mission into an odyssey of danger.