Safety factor—
Finally he looked up. He had computed exactly how much spare fuel he had, how much he could afford to waste. It was a small figure—too small, perhaps.
He turned to the radio. "Ganymede?"
"Where are you, Postal Ship?"
"I'm in a tight orbit about a hundred miles up," Preston said. "Give me the figures on the circumference of your Dome, Ganymede?"
"Seven miles," the colonist said. "What are you planning to do?"
Preston didn't answer. He broke contact and scribbled some more figures. Seven miles of iceworms, eh? That was too much to handle. He had planned on dropping flaming fuel on them and burning them out, but he couldn't do it that way.
He'd have to try a different tactic.
Down below, he could see the blue-white ammonia ice that was the frozen atmosphere of Ganymede. Shimmering gently amid the whiteness was the transparent yellow of the Dome beneath whose curved walls lived the Ganymede Colony. Even forewarned, Preston shuddered. Surrounding the Dome was a living, writhing belt of giant worms.
"Lovely," he said. "Just lovely."