Descent

Isoke Ngozi clambered down an old lava flow, the clawed pads of his pressure-suit armor the only thing holding him from crashing down the torturous slope. He had been alone on the mountain for hours.

The faded yellow-gray of the night sky of Venus, unbroken cloud cover tinted orange by the dull glow of the ground, only emphasized that isolation. No one knew exactly where he was. Few knew he was out here at all.

The bulk of the improvised equipment rack he wore warred with his climbing reflexes, but he needed the survival gear, especially the spare pressure tanks. His friends, trapped in their tank-like crawler high on the slopes of this sporadically active volcano, were depending on him to find a support camp at the base of the mountain and start a rescue operation. Whether they could hold out longer than he was in doubt.

Two of his oxygen tanks and one containing hydrogen fuel had been emptied and discarded. The numbers should have been equal. He shared the oxygen with the fuel cell that powered the hydraulics, instrumentation and the cooling system that provided his only active defense against the heat under pressure surrounding him. Only the fuel cell used hydrogen, although in double the quantity of oxygen. His own body was consuming the additional oxygen through the effort of his descent. He was attempting to maintain the greatest pace he could without overexerting himself and wasting that oxygen. Using manual steering with the walker program would cut back on his own consumption, but the robot-control software would not be able to negotiate the broken terrain quickly enough to be of any use.

If he selected fully autonomous navigation, and it ran into a dead end, the computer would begin to trace one edge of traversable territory in an attempt to regain the original course setting. If the way was passable, and Isoke had no assurance of that, the method would work, eventually. Unfortunately, the suit instruments had no ability to detect a navigable route at any great distance or beyond visual obstructions, just as the navigation program lacked the imagination to take shortcuts over unmapped territory.

The only known course, the route of their ascent along a ridge of the mountain, had been cut off by the first eruption, a pair of lateral outbreaks bracketing their position. The meandering alternative the navigator would choose would take far too long. Not only would he be finished but the others as well.

The lava formation spread into a fan over a relatively level area and abruptly gave out. Isoke began a lope on the loose gravel left exposed while trying to keep from slipping. He noticed with alarm that the uncertain footing was causing him to use far more oxygen than he could allow. Reluctantly he slowed to a walk.

The navigator program could handle this stretch. He fed in the course, requested maximum reasonable speed and settled back in his harness. The robot began to run, covering three meters with each low, leaping stride through the dense air. Isoke could see no obstacles ahead, either through his viewport or on his radar display. He checked all his instruments and, though his instincts rebelled, closed his viewport shields against both possible mishaps and the temptation to watch the bounding landscape and wearily succumbed to troubled sleep.

An alarm snapped him into panicky alertness. The window visors flipped open automatically before his vision cleared. He was charging headlong down a crazily tilted wall of bare rock that dropped away sharply to his left. He almost terminated the navigation directive before he realized that the alarm had not been caused by the hair-raising descent. In order to avoid the cliff edge, the robot had been forced to change course.

Isoke silenced the alarm. Almost afraid to watch, he forced himself to endure the plunge. The slope steepened until a second signal sounded. The walker program had finally agreed with his nervous system and was starting to slow the suit down.

Not long afterward, a third warning heralded a sharp change in course. Unable to look for holds, the software was directing the robot along the best path it could handle, in this case, almost back the way he had come.

Isoke canceled the order to the navigator. The machine slowed to a halt. Using the manual controls, he began to climb sideways on the nearly featureless rock in search of a ledge. There was one, a hundred meters below. He angled his way down, picking his footholds with extreme care. The artificial feet seemed suddenly much too large and far away. The rack assembly holding the spare tanks made him feel as if he were strapped into a bookcase. The rough stone left scratches in the protective coating on the arms and legs of his suit but it didn't matter. By the time the corrosives in the atmosphere could eat through that armor, he and his friends would all have been dead for days, at the least. And if he slipped. ... He could spare neither the time nor the effort nor the attention from his meticulous descent to care. He scrambled painstakingly on. He had just reached the ledge and was trying to catch his breath when there was a rumble on the mountainside far above him.

Isoke had never heard an avalanche before, but he was certain of its identity. He felt equally certain of its path. He was like a beetle pinned to a display card. There was no place to hide on the ledge.

What about below? The ledge formed the top of an overhanging cliff. Kneeling awkwardly beneath his supply rack, Isoke spotted a small crack just below the edge and fired a piton bolt into it. The rumble became a roar. He hooked his belt winch to the padeye and tugged at it. The radar unit clamored for attention. He looked up to see the sky above his hatch viewport transform into a rapidly descending ceiling of broken rock.

Desperately he hurled himself headfirst over the edge of the precipice. The anchor hookup immediately flipped him upright. The spare pressure tanks strained momentarily against the equipment netting, but the improvised restraint held. As Isoke's hatch rim clanged against the cliff, he released the safety-cable brake.

A cataract of debris thundered past him as the winch spun out. He dropped like a frightened spider between the two deadly walls, one solid, bleak and unyielding, the other a churning mass of fragments ranging from fine particles carried along by the backwash of the fall to boulders the size of jeeps. He was enveloped in a cloud of swirling dust.

Small rocks began to batter his armor. Isoke...