 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. 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. In his mind the need to escape became an obsession on top of the other psychotic states normal to a Moon-colonist. The second luxury liner took off with only four passengers and turned back before reaching the Moon. But Sattell undoubtedly dealt with it fully in his desperate writings back to Earth.
 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.