"Simple enough," Nolan replied. "The men who were left behind pulled out and left me at the camp when they heard about your rescue. They probably didn't care to kill me if they didn't have to. They left while I was asleep and probably went over the pole into Russia. They took my ship, but I was able to call for help with the radio. What happens to them doesn't matter anyway. We'll probably never hear of them again. "I suppose it won't be long before we have colonies on all the planets with that neutron rocket you mentioned." "It'll be a while yet," Roger said. "There are a lot of problems involved in the development of a neutron rocket, and as long as we have to use a fuel processed by passing hydrogen through an electric arc and into an expensive organic compound at low temperatures, space travel will be too expensive for anything more than the exploration expeditions that have been sent to Mars and Venus." The voice of the announcer interrupted them. "The spaceship _Goddard_ is loading passengers from tunnel eleven. All passengers must be aboard in twenty minutes." Roger and Linda rose from the table. "That's our ship," Roger said. "We'd better get aboard. Goodbye, Professor Nolan. I hope we meet again." "Goodbye, young fellow, and good luck." Nolan gripped Roger's hand. * * * * * Thirty minutes later the professor stood at the window and watched the preparations for blast off. The tail gantry crane moved away from the rocket, and a siren blared forth its warning. The booster motors were started, splashing green flame into the pit and shaking the ground with their roar. The tall ship rose slowly at first, and then more rapidly as it climbed a column of green flame into the clearing sky. It grew small and disappeared. A few minutes later the ship's atomic drive came to life like a tiny new sun that was a beacon on the path to space.