Nowadays, one could always tell when Hal was about to make an unscheduled announcement. Routine, automatic reports, or replies to questions that had been put to him, had no preliminaries; but when he was initiating his own outputs there would be a brief electronic throat-clearing. It was an idiosyncrasy that he had acquired during the last few weeks; later, if it became annoying, they might do something about it. But it was really quite useful, since it alerted his audience to stand by for something unexpected.

Poole was asleep, and Bowman was reading on the control deck, when Hal announced:

"Er – Dave, I have a report for you."

"What's up?"

"We have another bad AE-35 unit. My fault predictor indicates failure within twenty-four hours."

Bowman put down his book and stared thoughtfully at the computer console. He knew, of course, that Hal was not really there, whatever that meant. If the computer's personality could be said to have any location in space, it was back in the sealed room that contained the labyrinth of interconnected memory units and processing grids, near the central axis of the carrousel. But there was a kind of psychological compulsion always to look toward the main console lens when one addressed Hal on the control deck, as if one were speaking to him face to face. Any other attitude smacked of discourtesy.

"I don't understand it, Hal. Two units can't blow in a couple of days."

"It does seem strange, Dave. But I assure you there is an impending failure."

"Let me see the tracking alignment display."

He knew perfectly well that this would prove nothing, but he wanted time to think. The expected report from Mission Control had still not arrived; this might be the moment to do a little tactful probing.

There was the familiar view of Earth, now waxing past the half-moon phase as it swept toward the far side of the Sun and began to turn its full daylight face toward them. It was perfectly centered on the cross-wires; the thin pencil of the beam still linked Discovery to her world of origin. As, of course, Bowman knew it must do. If there had been any break in communication, the alarm would already have sounded.

"Have you any idea," he said, "what's causing the fault?"

It was unusual for Hal to pause so long. Then he answered:

"Not really, Dave. As I reported earlier, I can't localize the trouble."

"You're quite certain," said Bowman cautiously, "that you haven't made a mistake? You know that we tested the other AB-35 unit thoroughly, and there was nothing wrong with it."

"Yes, I know that. But I can assure you that there is a fault. If it's not in the unit, it may be in the entire subsystem."

Bowman drummed his fingers on the console. Yes, that was possible, though it might be very difficult to prove – until a breakdown actually occurred and pinpointed the trouble.

"Well, I'll report it to Mission Control and we'll see what they advise." He paused, but there was no reaction.

"Hal," he continued, "is something bothering you – something that might account for this problem?"

Again there was that unusual delay. Then Hal answered, in his normal tone of voice:

"Look, Dave, I know you're trying to be helpful. But the fault is either in the antenna system – or in your test procedures. My information processing is perfectly normal. If you check my record, you'll find it completely free from error."

"I know all about your service record, Hal – but that doesn't prove you're right this time. Anyone can make mistakes."

"I don't want to insist on it, Dave, but I am incapable of making an error."

There was no safe answer to that; Bowman gave up the argument.

"All right, Hal," he said, rather hastily. "I understand your point of view. We'll leave it at that."

He felt like adding "and please forget the whole matter." But that, of course, was the one thing that Hal could never do.

It was unusual for Mission Control to waste radio bandwidth on vision, when a speech circuit with teletype confirmation was all that was really necessary. And the face that appeared on the screen was not that of the usual controller; it was the Chief Programmer, Dr. Simonson. Poole and Bowman knew at once that this could only mean trouble.

"Hello, X-ray-Delta-One – this is Mission Control. We have completed the analysis of your AE-35 difficulty, and both our Hal Nine Thousands are in agreement. The report you gave in your transmission two-one-four-six of a second failure prediction confirms the diagnosis.

"As we suspected, the fault does not lie in the AE-35 unit, and there is no need to replace it again. The trouble lies in the prediction circuits, and we believe that it indicates a programming conflict which we can only resolve if you disconnect your Nine Thousand and switch to Earth Control Mode. You will therefore take the following steps, beginning at 2200 Ship Time -"

The voice of Mission Control faded out. At the same moment, the Alert sounded, forming a wailing background to Hal's "Condition Yellow! Condition Yellow!"

"What's wrong?" called Bowman, though he had already guessed the answer.

"The AE-35 unit has failed, as I predicted."

"Let me see the alignment display."

For the first time since the beginning of the voyage, the picture had changed. Earth had begun to drift from the cross-wires; the radio antenna was no longer pointing toward its target.

Poole brought his fist down on the alarm cutout, and the wailing ceased. In the sudden silence that descended upon the control deck, the two men looked at each other with mingled embarrassment and concern.

"Well I'm damned," said Bowman at last.

"So Hal was right all the time."

"Seems that way. We'd better apologize."

"There's no need to do that," interjected Hal. "Naturally, I'm not pleased that the AE-35 unit has failed, but I hope this restores your confidence in my reliability."

"I'm sorry about this misunderstanding, Hal," replied Bowman, rather contritely.

"Is your confidence in me fully restored?"

"Of course it is, Hal."

"Well, that's a relief. You know that I have the greatest possible enthusiasm for this mission."

"I'm sure of it. Now please let me have the manual antenna control."

"Here it is."

Bowman did not really expect this to work, but it was worth trying. On the alignment display, Earth had now drifted completely off the screen. A few seconds later, as he juggled with the controls, it reappeared; with great difficulty, he managed to jockey it toward the central crosswires. For an instant, as the beam came into line, contact was resumed and a blurred Dr. Simonson was saying "... please notify us immediately if Circuit K King R Rob." Then, once again, there was only the meaningless murmuring of the universe.

"I can't hold it," said Bowman, after several more attempts. "It's bucking like a bronco – there seems to be a spurious control signal throwing it off."

"Well – what do we do now?"

Poole's question was not one that could be easily answered. They were cut off from Earth, but that in itself did not affect the safety of the ship, and he could think of many ways in which communication could be restored. If the worst came to the worst, they could jam the antenna in a fixed position and use the whole ship to aim it. That would be tricky, and a confounded nuisance when they were starting their terminal maneuvers – but it could be done, if all else failed.

He hoped that such extreme measures would not be necessary. There was still one spare AE-35 unit – and possibly a second, since they had removed the first unit before it had actually broken down. But they dared not use either of these until they had found what was wrong with the system. If a new unit was plugged in, it would probably burn out at once.