Captain Greene shook his shaggy head and studied Allerton with patient eyes. "You're making a mistake," he said. "You'll be back." The inside of the spaceship was quiet now, not with the silence of the tomb, but with the silence of barely inaudible echoes as if Allerton might still be able to hear the crew clomping about the companionways on metal-shod feet if only he knew how to listen. He buried the notion under the sweet anticipation of homecoming and said, "I don't think so, Captain. This is