The cloud of fragments possessed the same trajectory as the missile originally had. At the rate it was overtaking RI 276, it would soon pass the ship by. The autopilot of RI 276 had no intention of letting this happen, of course. At the correct instant, stage two thundered into life, and Harry Lightfoot was again smashed back into his acceleration couch. Almost absentmindedly, the ship continued to minister to his needs. Its attention was focused on its mission. After a while, the ground computer sent some instructions to the ship. The navigation computer converted these into a direction, and pointed a radar antenna in that direction. The antenna sent forth a stream of questing pulses, which quickly returned, confirming the direction and distance to the oncoming cloud of missile fragments. A little while later, fuel pumps began to whine somewhere in the tail of the ship. Then the acceleration dropped to zero as the second-stage thrust was terminated. There was a series of thumps as explosive bolts released the second stage. The whine of the pumps dropped in pitch as fuel gushed through them, and acceleration returned in a rush. The acceleration lasted for a few seconds, tapered off quickly, and ended. A light winked on on the instrument panel as the ship announced its mission was accomplished.
Major Harry Lightfoot, fighter pilot, felt a glow of satisfaction as he saw the light come on. He might not have reflexes fast enough to pilot the ship up here; he might not be able to survive the climb to intercept without the help of a lot of fancy equipment; but he was still necessary. He saw still one step ahead of this complex robot which had carried him up here. It was his human judgment and his ability to react correctly in an unpredictable situation which were needed to locate the warhead from among the cluster of decoys and destroy it. This was a job no merely logical machine could do. When all was said and done, the only purpose for the existence of this magnificent machine was to put him where he was now; in the same trajectory as the missile, and slightly behind it.
Harry Lightfoot reached for a red-handled toggle switch at the top of the instrument panel, clicked it from AUTO to MANUAL, and changed his status from passenger to pilot. He had little enough time to work. He could not follow the missile down into the atmosphere; his ship would burn up. He must begin his pull-out at not less than two hundred miles altitude. That left him one hundred eighty-three seconds in which to locate and destroy the warhead. The screen in the center of his instrument panel could show a composite image of the space in front of his ship, based on data from a number of sensing elements and detectors. He switched on an infrared scanner. A collection of spots appeared on the screen, each spot indicating by its color the temperature of the object it represented. The infrared detector gave him no range information, of course. But if the autopilot had done its job well, the nearest fragment would be about ten miles away. Thus even if he set off the enemy warhead, he would be safe. At that range the ship would not suffer any structural damage from the heat, and he could be down on the ground and in a hospital before any radiation effects could become serious.
He reflected quickly on the possible temperature range of the missile components. The missile had been launched from Central Asia, at night, in January. There was no reason to suppose that the warhead had been temperature-controlled during the pre-launch countdown. Thus it probably was at the ambient temperature of the launch site. If it had been fired in the open, that might be as low as minus 70° F. Had it been fired from a shelter, that might be as high as 70° F. To leave a safety margin, he decided to reject only those objects outside the range plus or minus 100° F. There were two fragments at 500° F. He rejected these as probably fragments of the engine. Six more exhibited a temperature of near minus 320° F. These probably came from the liquid oxygen tanks. They could be rejected. That eliminated eight of the objects on the screen. He had nineteen to go. It would be a lot slower for the rest, too.
He switched on a radar transmitter. The screen blanked out almost completely. The missile had included a micro-wave transmitter, to act as a jammer. It must have been triggered on by his approach. It obviously hadn't been operating while the ship was maneuvering into position. Had it been transmitting then, the autopilot would simply have homed on it. He switched the radar to a different frequency. That didn't work. The screen was still blank, indicating that the jammer was sweeping in frequency. He next tried to synchronize his radar pulses with the jammer, in order to be looking when it was quiet. The enemy, anticipating him, had given the jammer a variable pulse repetition rate. He switched off the transmitter, and scanned the radar antenna manually. He slowly swung it back and forth, attempting to fix the direction of the jammer by finding the direction of maximum signal strength. He found that the enemy had anticipated him again, and the jammer's signal strength varied. However, he finally stopped the antenna, satisfied that he had it pointed at the jammer. The infrared detector confirmed that there was something in the direction the antenna pointed, but it appeared too small to be the warhead.
He then activated the manual piloting controls. He started the fuel pumps winding up, and swung the ship to point normal to the line-of-sight to the jammer. A quick blast from the rockets sent the image of the jammer moving sideways across the screen. But, of greater importance, two other objects moved across the screen faster than the jammer, indicating they were nearer the ship than was the jammer. He picked the one which appeared the nearest to him, and with a series of maneuvers and blasts from the rockets placed the object between himself and the jammer. He switched the radar on again. Some of the jammer signal was still leaking through, but the object, whatever it was, made an effective shield. The radar images were quite sharp and clear.
He glanced at the clock. Nullifying the jammer had cost him seventy-five seconds. He'd have to hurry, in order to make up for that time. The infrared detector showed two targets which the radar insisted weren't there. He shifted radar frequency. They still weren't there. He decided they were small fragments which didn't reflect much radar energy, and rejected them. He set the radar to a linearly polarized mode. Eight of the targets showed a definite amplitude modulation on the echo. That meant they were rotating slowly. He switched to circular polarization, to see if they presented a constant area to the radar beam. He compared the echoes for both modes of polarization. Five of the targets were skin fragments, spinning about an axis skewed with respect to the radar beam. These he rejected. Two more were structural spars. They couldn't conceal a warhead. He rejected them. After careful examination of the fine structure of the echo from the last object, he was able to classify it as a large irregular mass, probably a section of computer, waving some cables about. Its irregularity weighed against its containing the warhead. Even if it didn't burn up in the atmosphere, its trajectory would be too unpredictable.
He turned to the rest of the targets. Time was getting short. He extracted every conceivable bit of information out of what his detectors told him. He checked each fragment for resonant frequencies, getting an idea of the size and shape of each. He checked the radiated infrared spectrum. He checked the decrement of the reflected radar pulse. Each scrap of information was an indication about the identity of the fragments. With frequent glances at the clock, constantly reminding him of how rapidly his time was running out, he checked and cross-checked the data coming in to him. Fighting to keep his mind calm and his thoughts clear, he deduced, inferred, and decided. One fragment after another, he sorted, discarded, rejected, eliminated, excluded. Until the screen was empty.