He received the O.K. for the procedure, and parked the pod some twenty feet away from the base of the antenna support. There was no danger that it would drift off into space; nevertheless, he clamped a manipulator hand over one of the many short sections of ladder rung strategically mounted on the outer hull.
Then he checked the systems of his pressure suit, and, when he was quite satisfied, bled the air out of the pod. As Betty’s atmosphere hissed away into the vacuum of space, a cloud of ice crystals formed briefly around him, and the stars were momentarily dimmed.
There was one thing more to do before he left the pod. He switched over from manual to remote operation, putting Betty now under control of Hal. It was a standard safety precaution; though he was still secured to Betty by an immensely strong spring-loaded cord little thicker than cotton, even the best safety lines had been known to fail. He would look a fool if he needed his vehicle – and was unable to call it to his assistance by passing instructions to Hal.
The door of the pod swung open, and he drifted slowly out into the silence of space, his safety line unreeling behind him. Take things easy – never move quickly – stop and think – these were the rules for extravehicular activity. If one obeyed them, there was never any trouble.
He grabbed one of Betty’s external handholds, and removed the spare AE-35 unit from the carry-pouch where it had been stowed, kangaroo fashion. He did not stop to collect any of the pod’s collection of tools, most of which were not designed for use by human bands. All the adjustable wrenches and keys he was likely to need were already attached to the belt of his suit.
With a gentle push, he launched himself toward the gimbaled mounting of the big dish that loomed like a giant saucer between him and the Sun. His own double shadow, thrown by Betty’s spotlights, danced across the convex surface in fantastic patterns as he drifted down the twin beams. But here and there, he was surprised to notice, the rear of the great radio mirror sparkled with dazzlingly brilliant pinpoints of light.
He puzzled over these for the few seconds of his silent approach, then realized what they were. During the voyage, the reflector must have been penetrated many times by micrometeors; he was seeing the sunlight blazing through the tiny craters. They were all far too small to have affected the system’s performance appreciably.
As he was moving very slowly, he broke the gentle impact with his outstretched arm, and grabbed hold of the antenna mounting before he could rebound. He quickly hooked his safety belt to the nearest attachment; that would give him something to brace against when he used his tools. Then he paused, reported the situation to Bowman, and considered his next step.
There was one minor problem; he was standing – or floating – in his own light, and it was hard to see the AE-35 unit in the shadow he cast. So he ordered Hal to swing the spots off to one side, and after a little experimenting got a more uniform illumination from secondary light reflected off the back of the antenna dish.
For a few seconds, he studied the small metal hatch with its four wire-secured locking nuts. Then, muttering to himself, “Tampering by unauthorized personnel invalidates the manufacturer’s guarantee,” he snipped the wires and started to untwist the nuts. They were a standard size, fitting the zero-torque wrench that he carried. The tool’s internal spring mechanism would absorb the reaction as the nuts were unthreaded, so that the operator would have no tendency to spin around in reverse.
The four nuts came off without any trouble, and Poole stowed them carefully away in a convenient pouch. (One day, somebody had predicted, Earth would have a ring like Saturn’s, composed entirely of lost bolts, fasteners, and even tools that had escaped from careless orbital construction workers.) The metal cover was a little sticky, and for a moment he was afraid it might have cold-welded into place; but after a few taps it came loose, and he secured it to the antenna mounting by a large crocodile clip.
Now he could see the electronic circuitry of the AE-35 unit. It was in the form of a thin slab, about the size of a postcard, gripped by a slot just large enough to hold it. The unit was secured in place by two locking bars, and had a small handle so that it could be easily removed.
But it was still operating, feeding the antenna the impulses that kept it aimed at the far-off pinpoint of Earth. If it was pulled out now, all control would be lost, and the dish would slam round to its neutral or zero-azimuth position, pointing along the axis of Discovery. And this could be dangerous; it might crash into him as it rotated.
To avoid this particular hazard, it was only necessary to cut off power to the control system; then the antenna could not move, unless Poole knocked against it himself. There was no danger of losing Earth during the few minutes it would take him to replace the unit; their target would not have shifted appreciably against the background of the stars in such a brief interval of time.
“Hal,” Poole called over the radio circuit, “I am about to remove the unit. Switch off all control power to the antenna system.”
“Antenna control power off,” answered Hal.
“Here goes. I’m pulling the unit out now.”
The card slipped out of its slot with no difficulty; it did not jam, and none of the dozens of sliding contacts stuck. Within a minute, the spare was in place.
But Poole was taking no chances. He pushed himself gently away from the antenna mount, just in case the big dish went wild when power was restored. When he was safely out of range, he called to Hal: “The new unit should be operational. Restore control power.”
“Power on,” answered Hal. The antenna remained rock steady.
“Carry out fault prediction tests.”
Now microscopic pulses would be bouncing through the complex circuitry of the unit, probing for possible failures, testing the myriads of components to see that they all lay within their specified tolerances. This had been done, of course, a score of times before the unit had ever left the factory; but that was two years ago, and more than half a billion miles away. It was often impossible to see how solid-state electronic components could fail; yet they did.
“Circuit fully operational,” reported Hal after only ten seconds. In that time, he carried out as many tests as a small army of human inspectors.
“Fine,” said Poole with satisfaction. “Now replacing the cover.”
This was often the most dangerous part of an extravehicular operation: when a job was finished and it was merely a matter of tidying up and getting back inside the ship – that was when the mistakes were made. But Frank Poole would not have been on this mission if he had not been careful and conscientious. He took his time, and though one of the locking nuts almost got away from him, he caught it before it had traveled more than a few feet.
Fifteen minutes later he was jetting back into the space-pod garage, quietly confident that here was one job that need not be done again.
In this, however, he was sadly mistaken.
23 – Diagnosis
“Do you mean to say,” exclaimed Frank Poole, more surprised than annoyed, “that I did all that work for nothing?”
“Seems like it,” answered Bowman. “The unit checks out perfectly. Even under two hundred percent overload, there’s no fault prediction indicated.”
The two men were standing in the tiny workshop-cum-lab in the carrousel, which was more convenient than the space-pod garage for minor repairs and exanimations. There was no danger, here, of meeting blobs of hot solder drifting down the breeze, or of completely losing small items of equipment that had decided to go into orbit. Such things could – and did – happen in the zero-gee environment of the pod bay.
The thin, card-sized plate of the AE-35 unit lay on the bench under a powerful magnifying lens. It was plugged into a standard connection frame, from which a neat bundle of multicolored wire led to an automatic test set, no bigger than an ordinary desk computer. To check any unit it was only necessary to connect it up, slip in the appropriate card from the “trouble-shooting” library, and press a button. Usually the exact location of the fault would be indicated on a small display screen, with recommendations for action.
“Try it yourself,” said Bowman, in a somewhat frustrated voice. Poole turned the OVERLOAD SELECT switch to X-2 and jabbed the TEST button. At once, the screen flashed the notice: UNIT OK.