"Check!"
Hadley cracked an air valve beside a circular air door. The hiss of entering air crescendoed and died, and then Hadley cracked the door that opened in upon the huge driver tube. With casual disregard for the annular electrodes that would fill the tube with sudden death if the pilot sent the driving power surging into the electrodes, Hadley climbed to the top of the tube and used a spanner to remove four huge bolts. A handy differential pulley permitted him to lower the near-exhausted cathode from the girders to the air door, where it was hauled to the deck. A fresh cathode was slung to the pulley and hoisted to place. Hadley bolted it tight and clambered back into the ship. He closed the air door and the valve, and then opened the valve that led from the tube to outer space. The tube evacuated and Hadley spoke once more to the pilot room.
"Hadley to Greenland: Tube 4 ready."
"Check."
The operation was repeated on tube 2, and then Pilot Greenland said: "Fade-back beginning. Power diminishing on 1 and 3, increasing on 2 and 4. Power equalized, acceleration two G as before. Deviation from norm: two-tenths G."
Hadley grinned at the crew. "You'd think Greenland did all that himself, the way he talks. If it weren't for autopilots, we'd have been all over the sky."
Tom Bennington laughed. He was an old-timer, and he said in a reminiscent tone: "I remember when we did that on manual. There were as many cases of mal-de-void during cathode change as during turnover. Autopilots are the nuts—look! We're about to swing right now, and I'll bet a fiver that the folks below won't know a thing about it."
A coincidence of mammoth proportions occurred at precisely that instant. It was a probability that made the chance of drawing a royal flush look like the chances of tomorrow coming on time. It was, in fact, one of those things that they said couldn't possibly happen, which went to prove only how wrong they were. It hadn't happened yet and probably wouldn't happen again for a million million years, but it did happen once.
Turnover was about to start. A relay circuit that coupled the meteor-spotter to the autopilot froze for a bare instant, and the coincidence happened between the freezing of the relay contacts and the closing of another relay whose purpose it was to shunt the coupler circuits through another line in case of relay failure. In the conceivably short time between the failure and the device that corrected failure, the Ariadne hit a meteor head-on.