concealing the most deadly needle of alltime. No ground-controlled intercept scheme had any hope of selectingthe warhead from among that deceptive cloud and destroying it.
The cloud of fragments possessed the same trajectory as the missileoriginally had. At the rate it was overtaking RI 276, it would soon passthe ship by. The autopilot of RI 276 had no intention of letting thishappen, of course. At the correct instant, stage two thundered intolife, and Harry Lightfoot was again smashed back into his accelerationcouch. Almost absentmindedly, the ship continued to minister to hisneeds. Its attention was focused on its mission. After a while, theground computer sent some instructions to the ship. The navigationcomputer converted these into a direction, and pointed a radar antennain that direction. The antenna sent forth a stream of questing pulses,which quickly returned, confirming the direction and distance to theoncoming cloud of missile fragments. A little while later, fuel pumpsbegan to whine somewhere in the tail of the ship. Then the accelerationdropped to zero as the second-stage thrust was terminated. There was aseries of thumps as explosive bolts released the second stage. The whineof the pumps dropped in pitch as fuel gushed through them, andacceleration returned in a rush. The acceleration lasted for a fewseconds, tapered off quickly, and ended. A light winked on on theinstrument panel as the ship announced its mission was accomplished.
Major Harry Lightfoot, fighter pilot, felt a glow of satisfaction as hesaw the light come on. He might not have reflexes fast enough to pilotthe ship up here; he might not be able to survive the climb to interceptwithout the help of a lot of fancy equipment; but he was stillnecessary. He saw still one step ahead of this complex robot which hadcarried him up here. It was his human judgment and his ability to reactcorrectly in an unpredictable situation which were needed to locate thewarhead from among the cluster of decoys and destroy it. This was a jobno merely logical machine could do. When all was said and done, the onlypurpose for the existence of this magnificent machine was to put himwhere he was now; in the same trajectory as the missile, and slightlybehind it.
Harry Lightfoot reached for a red-handled toggle switch at the top ofthe instrument panel, clicked it from AUTO to MANUAL, and changed hisstatus from passenger to pilot. He had little enough time to work. Hecould not follow the missile down into the atmosphere; his ship wouldburn up. He must begin his pull-out at not less than two hundred milesaltitude. That left him one hundred eighty-three seconds in which tolocate and destroy the warhead. The screen in the center of hisinstrument panel could show a composite image of the space in front ofhis ship, based on data from a number of sensing elements and detectors.He switched on an infrared scanner. A collection of spots appeared onthe screen, each spot indicating by its color the temperature of theobject it represented. The infrared detector gave him no rangeinformation, of course. But if the autopilot had done its job well, thenearest fragment would be about ten miles away. Thus even if he set offthe enemy warhead, he would be safe. At that range the ship would notsuffer any structural damage from the heat, and he could be down on theground and in a hospital before any radiation effects could becomeserious.
He reflected quickly on the possible temperature range of the missilecomponents. The missile had been launched from Central Asia, at night,in January. There was no reason to suppose that the warhead had beentemperature-controlled during the pre-launch countdown. Thus it probablywas at the ambient temperature of the launch site. If it had been firedin the open, that might be as low as minus 70 deg. F. Had it been fired froma shelter, that might be as high as 70 deg. F. To leave a safety margin, hedecided to reject only those objects outside the range plus or minus100 deg. F. There were two fragments at 500 deg. F. He rejected these asprobably fragments of the engine. Six more exhibited a temperature ofnear minus 320 deg. F. These probably came from the liquid oxygen tanks.They could be rejected. That eliminated eight of the objects on thescreen. 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 almostcompletely. The missile had included a micro-wave transmitter, to act asa jammer. It must have been triggered on by his approach. It obviouslyhadn't been operating while the ship was maneuvering into position. Hadit been transmitting then, the autopilot would simply have homed on it.He switched the radar to a different frequency. That didn't work. Thescreen was still blank, indicating that the jammer was sweeping infrequency. He next tried to synchronize his radar pulses with thejammer, 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 ofthe jammer by finding the direction of maximum signal strength. He foundthat the enemy had anticipated him again, and the jammer's signalstrength varied. However, he finally stopped the antenna, satisfied thathe had it pointed at the jammer. The infrared detector confirmed thatthere was something in the direction the antenna pointed, but itappeared too small to be the warhead.
He then activated the manual piloting controls. He started the fuelpumps winding up, and swung the ship to point normal to theline-of-sight to the jammer. A quick blast from the rockets sent theimage of the jammer moving sideways across the screen. But, of greaterimportance, two other objects moved across the screen faster than thejammer, indicating they were nearer the ship than was the jammer. Hepicked the one which appeared the nearest to him, and with a series ofmaneuvers and blasts from the rockets placed the object between himselfand the jammer. He switched the radar on again. Some of the jammersignal was still leaking through, but the object, whatever it was, madean effective shield. The radar images were quite sharp and clear.
He glanced at the clock. Nullifying the jammer had cost him seventy-fiveseconds. He'd have to hurry, in order to make up for that time. Theinfrared detector showed two targets which the radar insisted weren'tthere. He shifted radar frequency. They still weren't there. He decidedthey were small fragments which didn't reflect much radar energy, andrejected them. He set the radar to a linearly polarized mode. Eight ofthe targets showed a definite amplitude modulation on the echo. Thatmeant they were rotating slowly. He switched to circular polarization,to see if they presented a constant area to the radar beam. He comparedthe echoes for both modes of polarization. Five of the targets were skinfragments, spinning about an axis skewed with respect to the radar beam.These he rejected. Two more were structural spars. They couldn't conceala warhead. He rejected them. After careful examination of the finestructure of the echo from the last object, he was able to classify itas a large irregular mass, probably a section of computer, waving somecables about. Its irregularity weighed against its containing thewarhead. Even if it didn't burn up in the atmosphere, its trajectorywould be too unpredictable.
He turned to the rest of the targets. Time was getting short. Heextracted every conceivable bit of information out of what his detectorstold him. He checked each fragment for resonant frequencies, getting anidea of the size and shape of each. He checked the radiated infraredspectrum. He checked the decrement of the reflected radar pulse. Eachscrap of information was an indication about the identity of thefragments. With frequent glances at the clock, constantly reminding himof how rapidly his time was running out, he checked and cross-checkedthe data coming in to him. Fighting to keep his mind calm and histhoughts clear, he deduced, inferred, and decided. One fragment afteranother, he sorted, discarded, rejected, eliminated, excluded. Until thescreen was empty.
Now what? Had the enemy camouflaged the warhead so that it looked like asection of the missile's skin? Not likely. Had he made a mistake in hisidentification of the fragments? Possibly, but there wasn't time torecheck every fragment. He decided that the most likely event was thatthe warhead was hidden by one of the other fragments. He swung the ship;headed it straight for the object shielding him from the jammer, whichhad turned out to be a section from the fuel tank. A short blast fromthe
rockets sent him drifting toward the object. One image on the screenbroadened; split in two. A hidden fragment emerged from behind one ofthe ones he had examined. He rejected it immediately. Its temperaturewas too low. He was almost upon the fragment shielding him from thejammer. If he turned to avoid it, the jammer would blank-out his radaragain. He thought back to his first look at the cloud of fragments.There had been nothing between his shield and the jammer. The onlyremaining possibility, then, was that the warhead was being hidden fromhim by the jammer itself. He would have to look on the other side of thejammer, using the ship itself as a shield.
He swung out from behind the shielding fragment, and saw his radarimages blotted out. He switched off the radar, and aimed the shipslightly to one side of the infrared image of the jammer. Another blastfrom the rockets sent him towards the jammer. Without range informationfrom the radar, he would have to guess its distance by