43. Fail-Safe
Five kilometres from the terminus, driver-pilot Rupert Chang had reduced speed yet again. Now, for the first time, the passengers could see the face of the Tower as something more than a featureless blur dwindling away to infinity in both directions. Upwards, it was true, the twin grooves along which they were riding still stretched forever-or at least for twenty-five thousand kilometres, which on the human scale was much the same. But downwards, the end was already in sight. The truncated base of the Tower was clearly silhouetted against the verdant green background of Taprobane, which it would reach and unite with in little more than a year.
Across the display panel, the red ALARM symbols flashed yet again. Chang studied them with a frown of annoyance, then pressed the RESET button. They flickered once, then vanished.
The first time this had happened, two hundred kilometres higher, there had been a hasty consultation with Midway Control. A quick check of all systems had revealed nothing amiss; indeed, if all the warnings were to be believed, the transporter's passengers were already dead. Everything had gone outside the limits of tolerance.
It was obviously a fault in the alarm circuits themselves, and Professor Sessui's explanation was accepted with general relief. The vehicle was no longer in the pure vacuum environment for which it had been designed; the ionospheric turmoil it had now entered was triggering the sensitive detectors of the warning systems.
“Someone should have thought of that,” Chang had grumbled. But, with less than an hour to go, he was not really worried. He would make constant manual checks of all the critical parameters; Midway approved, and in any case there was no alternative.
Battery condition was, perhaps, the item that concerned him most. The nearest charging point was two thousand kilometres higher up, and if they couldn't climb back to that they would be in trouble. But Chang was quite happy on this score; during the braking process the transporter's drive-motors had been functioning as dynamos, and ninety percent of its gravitational energy had been pumped back into the batteries. Now that they were fully charged, the surplus hundreds of kilowatts still being generated should be diverted into space through the big cooling fins at the rear. Those fins, as Chang's colleagues had often pointed out to him, made his unique vehicle look rather like an old-time aerial bomb. By this time, at the very end of the braking process, they should have been glowing a dull red. Chang would have been very worried indeed had he known that they were still comfortably cool. For energy can never be destroyed; it has to go somewhere. And very often it goes to the wrong place.
When the FIRE-BATTERY COMPARTMENT Sign came on for the third time, Chang did not hesitate to reset it. A real fire, he knew, would have triggered the extinguishers; in fact, one of his biggest worries was that these might operate unnecessarily. There were several anomalies on the board now, especially in the battery-charging circuits. As soon as the journey was over and he had powered down the transporter, Chang was going to climb into the motor-room and give everything a good old-fashioned eyeball inspection.
As it happened, his nose alerted him first, when there was barely more than a kilometre to go. Even as he stared incredulously at the thin wisp of smoke oozing out of the control board, the coldly analytical part of his mind was saying: “What a lucky coincidence that it waited until the end of the trip!”
Then he remembered all the energy being produced during the final braking, and had a pretty shrewd guess at the sequence of events. The protective circuits must have failed to operate, and the batteries had been overcharging. One fail-safe after another had let them down; helped by the ionospheric storm, the sheer perversity of inanimate things had struck again.
Chang punched the battery compartment fire-extinguisher button; at least that worked, for he could hear the muffled roar of the nitrogen blasts on the other side of the bulkhead. Ten seconds later, he triggered the VACUUM DUMP which would sweep the gas out into space – with, hopefully, most of the heat it had picked up from the fire. That too operated correctly; it was the first time that Chang had ever listened with relief to the unmistakeable shriek of atmosphere escaping from a space vehicle; he hoped it would also be the last.
He dared not rely on the automatic braking sequence as the vehicle finally crawled into the terminus; fortunately, he had been well rehearsed and recognised all the visual signals, so that he was able to stop within a centimetre of the docking adapter. In frantic haste, the airlocks were coupled together, and stores and equipment were hurled through the connecting tube…
And so was Professor Sessui, by the combined exertions of pilot, assistant engineer and steward, when he tried to go back for his precious instruments. The airlock doors were slammed shut just seconds before the engine compartment bulkhead finally gave way.
After that, the refugees could do nothing but wait in the bleak, fifteen-metre square chamber, with considerably fewer amenities than a well-furnished prison cell, and hope that the fire would burn itself out. Perhaps it was well for the passengers' peace of mind that only Chang and his engineer appreciated one vital statistic: the fully-charged batteries contained the energy of a large chemical bomb, now ticking away on the outside of the Tower.
Ten minutes after their hasty arrival, the bomb went off. There was a muffled explosion, which caused only slight vibrations of the Tower, followed by the sound of ripping and tearing metal. Though the breaking-up noises were not very impressive, they chilled the hearts of the listeners; their only means of transport was being destroyed, leaving them stranded twenty-five thousand kilometres from safety.
There was another, more protracted explosion – then silence; the refugees guessed that the vehicle had fallen off the face of the Tower. Still numbed, they started to survey their resources; and, slowly, they began to realise that their miraculous escape might have been wholly in vain.
44. A Cave in the Sky
Deep inside the mountain, amid the display and communications equipment of the Earth Operations Centre, Morgan and his engineering staff stood around the tenth-scale hologram of the Tower's lowest section. It was perfect in every detail, even to the four thin ribbons of the guiding tapes extending along each face. They vanished into thin air just above the floor, and it was hard to appreciate that, even on this diminished scale, they should continue downwards for another sixty kilometers – completely through the crust of the earth.
“Give us the cutaway,” said Morgan, “and lift the Basement up to eye level.”
The Tower lost its apparent solidity and became a luminous ghost – a long, thin-walled square box, empty except for the superconducting cables of the power supply. The very lowest section – the “Basement” was indeed a good name for it, even if it was at a hundred times the elevation of this mountain – had been sealed off to form a single square chamber, fifteen metres on a side.
“Access?” queried Morgan.
Two sections of the image started to glow more brightly. Clearly defined on the north and south faces, between the slots of the guidance tracks, were the outer doors of the duplicate airlocks – as far apart as possible, according to the usual safety precautions for all space habitats.
“They went in through the south door, of course,” explained the Duty Officer. “We don't know if it was damaged in the explosion.”
Well, there were three other entrances, thought Morgan – and it was the lower pair that interested him. This had been one of those afterthoughts, incorporated at a late stage in the design. Indeed, the whole Basement was an afterthought; at one time it had been considered unnecessary to build a refuge here, in the section of the Tower that would eventually become part of Earth Terminus itself.