"You mean you were riding an atom bomb?"
"Shucks, Mother, it's safe-the tamper around the fission material stops most of the radioactivity. Anyhow, the exposure is short."
"But suppose it went off?"
"It can't go off. To go off it has to either crash into the ground with a speed great enough to slap the sub-critical masses together as fast as its trigger- gun could do it, or you have to fire the trigger-gun by radio. Besides that, I had inserted the trigger guard-that's nothing more nor less than a little crowbar, but when it's in place not even a miracle could set it off, because you can't bring the sub-critical masses together."
"Maybe we had better drop this subject, Matt. It seems to make your mother nervous."
"But, Dad, she asked me."
"I know. But you still haven't told me what you inspect for."
"Well, in the first place, you inspect the bomb itself, but there's never anything wrong with the bomb. Anyhow, I haven't had the course for bomb- officer yet-he has to be a nucleonics engineer. You inspect the rocket motor, especially the fuel tanks. Sometimes you have to replace a little that has escaped through relief valves. But mostly you give her a ballistic check and check her control circuits."
"Ballistic check?"
"Of course, theoretically you ought to be able to predict where a prowler bomb would be every instant for the next thousand years. But it doesn't work out that way. Little things, the effect of the tidal bulges and the fact that the Earth is not a perfect uniform sphere and such, cause them to gradually wander a little away from the predicted orbits. After you find one and service it-they're never very far from where they ought to be-you correct the orbit by putting the whole ship in just precisely the proper trajectory and then put the rocket outside the ship again. Then you go after the next one."