 Why does the red-headed man come to the moon?
When it was first found, scientists descended into it to examine the exposed rock-strata and learn the history of the Moon before its craters were made. In the Moon's slight gravity, a man is really adjusted to existence when he has a well-developed case of agoraphobia. All of which happened back on Earth and a long time ago. He usually reached the moondozer about the time the ship began to brake for landing, and he watched it come in. The sun rose very, very slowly in what by convention was called the east. He'd come to the Moon in the first place because Sattell was here.
 To rescue Sattell, the diamonds are his payment.
 To kill Pop.  To steal the diamonds.  To rescue Sattell, the diamonds are his payment.  To destroy the lunar colony.