by Hal Clement
“Standard turn left four five point five,” Maria said without waiting for Belvew to report that his tanks were full.
“Left four five point five,” he acknowledged, banking promptly to seventy-four degrees. The group had established a half-Earth gravity as a “standard” coordinated turn on Titan. The ramjet’s wings, stubby as they were, could still give that much lift at ram speed below ten kilometers or so altitude. He snapped out of the turn in just over sixteen seconds, since mission speed was an equally standard one hundred meters per second when nothing else was demanded by circumstance.
“Your heading is good. You’ll reach the break in Leg Four in two hundred fifteen seconds from—NOW! Nose down so as to reach three hundred meters at that time. I’ve allowed for the speed increase at your present power setting, so don’t change it. On my time call, level off and do a standard right turn of one seventy seven point three. Start dropping cans at standard intervals ten seconds after you finish the turn. The leg ends at the twenty-second can.”
“Got it.” Belvew remembered again, with the aid of the blunt needle mounted in the suit under his chin, not to nod. There were no more words until the time call, and no more after it until the last of the pencil shaped and sized “cans”—containers for seismometers, thermometers, ultramagnetomers, and other gear—needed for the fourth leg of the planned seismic network had been ejected.
“Okay, Maria, take my hand.” Belvew nosed the jet upward as he spoke. All the others were listening and watching as their particular instruments allowed except Goodell, who was meticulously testing the output of each of the recently dropped cans. None interrupted the terse directions which formed the response to the pilot’s request, and he hurtled northward along the eastern shore of Lake Carver eight hundred meters above its surface with his earphones still silent. He knew they could follow his progress on their duplicates of his own Aitoff, and that he could expect to have his attention called to anything he seemed to be missing, so he concentrated on the screen area a third of the way from center to lower margin. This covered the region he would pass over in the next few seconds. It was only slightly distorted by the projection which let a single screen squeeze the full sphere into an ordinary human field of vision, though this mattered little; everyone had learned long ago to correct in their own minds even for the extreme warping at the edges. No part of the aircraft itself showed; though some of the two dozen cameras mounted in various parts of its skin did have wing, nose, or tail in their fields, the computer which blended their images on the single full-sphere display deleted these.
Unfortunately.
The liquid surface was currently glass-smooth ahead and left of the jet, though even Titanian winds could raise waves; gravity was weak and liquid density low, and the highest winds occurred over the lakes themselves where evaporation lowered the air density far more than temperature changes could. Belvew gave the lake only an occasional glance, keeping his main attention on the land ahead where the patch to be examined should be.
“Three minutes,” came Maria’s quiet voice. The others remained silent. “Two. You might be able to see it now.” The pilot scanned through his vision frequencies again, dodging the longer wave lengths which were more strongly absorbed by methane.
“I can, I think. Forget timing. I’m slowing to ten meters above stall—no, make that twenty for the first run—and going down to a hundred meters, and I’m cutting out the random reality reminder. If I lose track too seriously with where I really am we can cut my shift short later. I’ll recover. The air looks steady, but I don’t want another stall at this height.”
No one objected aloud, though there must have been mental reservations. Belvew was the pilot for now; it was up to him to weigh relative risks to the aircraft. Negative comments would have been distracting, and therefore dangerous as well as discourteous.
The smooth patch grew clearer as the seconds passed. It was larger than most, about half a kilometer across, roughly circular but with four or five extensions reaching out another hundred or hundred and fifty meters at irregular points around its circumference. It might have been an oversized amoeba as far as outline went. The color seemed to be basically black, though it reflected the pale reddish-orange of the Titianian high smog as though from glass.
No small details could be made out from the present altitude and speed. Gene banked to a much less than standard turn rate for this speed, swung in a wide, slow circle north of the patch, and made a second pass in the opposite direction. This time the reflection of the brighter section of southern sky where the sun was hiding could be made out; the surface looked more than ever like glass, as Maria had described the others on her map, but there were still no informative details.
He made two more runs, this time at thirty meters above the highest point of the patch and only two meters per second above ramstall, tense and ready to shift to rocket mode—to cap the intakes and send liquid and extra heat into the pipes at the slightest drop in thrust. He was not worried about the wings stalling; even those stubby structures had plenty of lift area in this atmosphere and gravity, and the jet had been designed so that they would go out at higher airspeed than any control surfaces.
Nevertheless, his attention was enough on his aircraft and far enough from the ground so that it was Barn who spotted the irregularity.
“There’s a hollow about ten meters across half way from the high point to the base of that northwest arm. It did funny things to the jet’s reflection as we passed this time, but I can’t see it now. I can’t decide exactly how deep it is, but it’s just a dent, not a real hole.”
“Did anyone else spot it?” asked Belvew. Most of them had, but none could give any better description. The pilot made another pass, this time devoting a dangerous amount of his attention to the surface below, and saw the feature for himself; but he could make out no more details than the others.
“You know we’re going to have to land sometime,” Goodell said in what was meant to be a thoughtful tone.
“I know.” Belvew was thinking too. There was half a minute’s pause before the remote-lab manager tried again.
“What time is better than now?” The pilot could answer that one.
“When we know more about the strength of that surface. If it’s just a crust, as the rain theory suggests, Oceanus could break through and smother the jet scoops in dust, or mud, or dirt, or whatever form the stuff under it happens to have.”
“You have plenty of cans. See what happens when one of them hits. You needn’t use its chute; let it hit as hard as Titan can make it.”
“Good idea.” The pilot, with much relief, cautiously raised his speed to standard—too sudden a boost to the flame could make the pipe frontfire—and climbed to a full kilometer. There was still no wind, but the patch was a harder target than he had anticipated. Without its parachute the slender container took much longer to lose the jet’s speed, as all had expected but none could estimate quantitatively. The first attempt overshot badly. Belvew couldn’t see it, but Inger and Collos followed it with other instruments until it buried itself beyond detection in ordinary, firm Titanian “soil” a hundred and fifty meters beyond the edge of the glassy patch.
The second try, with Barn calling the release moment, was much better and quite informative in its way. The can’s own instruments stopped radiating at the instant of impact, ending passive measurements, but Maria’s shortest viewing waves showed that the little machine, solid as it was, had shattered on contact. The surface seemed pretty strong. Belvew was less happy than he might have been; if the can had broken through undamaged it would have implied a crust too weak to take the jet’s weight, much less the impact of a poor landing just here and now.
As it was, the next test appeared to be up to him. He thought furiously. Would anything except an actual landing tell them what they needed to know?
The jet lacked landing gear in any ordinary sense; there were no wheels, floats, or real skids. Its belly was shaped into a double keel me
ant to give it catamaran stability in an attempted liquid landing and broad support on dubiously solid surfaces, though once stopped the body would sink to something like three quarters of its diameter in the best-guess mixture of Titan’s lakes. It would float a little deeper in pure methane. This was why no one wanted to make the first lake landing; it had not occurred to anyone until much too late even to calculate, much less test, the results of attempting a rocket mode start with the pipes totally immersed in liquid. The log of the Earth to Saturn orbit had several similar annoyed entries.
The keels were adequate landing skids on a solid surface; one could make a pass at just above wing stalling speed, grazing the apparently smooth hump. If he did it right, he might resolve the question of whether the patch was solid or crust. If the latter, of course, there would be no certainty about its ultimate strength until the jet came to a stop and the wings lost all their lift.
The convexity of the surface complicated the problem slightly. If he hit too hard, easy to do on the upslope side, the question of whether the crust was stronger than the jet’s belly and keels would also become relevant.
The initial landing, Earth days before, had been on a smooth shelf of ice near the foot of the steep side of what looked like a tilted block mountain; Titan seemed still active tectonically. There had been no trouble anticipated in detail, though of course the pilot—Inger, at that time—had kept alert for the unforeseen. This was fortunate, since the exhausts had started a thermal-shock crack in the ice which chased the jet for most of its landing slide. The pilot had just managed to avoid riding to the foot of the hill on several million tons of detached shelf by a final, quick shot of thrust. The three hours it had taken for the factory pod to climb to the bottom, get to a safe distance from the cliff face and the new pile of ice rubble, put down roots and start growing had been spent in a high state of tension. Not just by Inger.
When it seemed certain that no more pods would have to be sent out, the fact that only a short length of ice shelf remained for takeoff had to be faced. Inger had been forced to use more than normal thrust, and while he concentrated his attention straight ahead, the rest of the group watched another crack chase him along the shelf, and more ice rubble fall, bounce, and roll toward the new factory. There was no longer any ice platform to land on when he did get into the air. The two later descents to pick up cans, once the factory had matured, had been on “ordinary” ground and proved uneventful. The drag on the skids, which all had feared might stress the aircraft too highly—this was why the ice shelf had been chosen for the first touchdown—had been sharp but not dangerous, and the subsequent takeoffs had presented no problems except a rather larger demand for reaction mass than had been hoped.
Belvew remembered the ice landing vividly as he planned his present one. Some dangers were more foreseeable this time, but there was the chance that concentrating on these might lessen his readiness to respond to something unforeseen as promptly as his friend had done.
Well, Theia and Crius were still available at the orbiting station, and the chance had to be taken sometime. No one would blame him for losing Oceanus.
At least, not aloud.
He called for a wind check—even a few kilometers an hour could make a difference—and held a constant heading for ten kilometers while Inger adjusted a superimposed grid on his own screen’s image. Eventually the moving ground features followed one of the lines and let him tie their apparent motion.
“Only one point seven, from eighty seven,” was the verdict. Belvew swept out over the lake without asking Maria for a heading, lined up with the patch from a dozen kilometers to the west, and eased back on his power. He nosed up enough to split the result between descent and speed loss, and reached the shore fifty meters above the liquid and a scant two meters a second above ram stall. Chewing his lower lip, which fortunately affected no waldo controls, he closed the ram intakes and fed the liquid to the plasma arcs. There was a grunt of admiration which might have come from Goodell; the shift to rocket mode was almost perfectly smooth. The longitudinal accelerometer swung promptly to a negative reading, and stayed there as Belvew turned down his fires even more. He was approaching wing stall now, and began increasing the camber of his lifting surfaces toward the barrel-section shape which had been used so few times before, and never by him. He should, he suddenly realized, have done a few practice stalls two or three kilometers higher. He convinced himself quickly that breaking off the approach and going up to do this now was not really necessary but didn’t ask for anyone else’s opinion.
The rippled dust was fifty meters down—forty—thirty . . .
The glassy convexity loomed ahead, rising to meet his keels. He nosed up even more, killing descent briefly while airspeed continued to drop. The bulge kept rising toward him. Without orders, Inger began calling speed. The wings should maintain lift down to sixteen meters per second, Belvew knew, and the stall then should be smooth. Some levels of theory were pretty solidly established.
“Twenty-two zero—twenty-one nine—twenty-one eight . . .”
The keels were two meters from the bulge, and he nosed up still farther to keep them so as the airspeed continued to fall. That wouldn’t work much farther; past the top of the dome he’d have to drop the nose to make contact before stall, and that would speed him up. Not much in Titan’s gravity, but any would complicate the maneuver.
The side edges of his screen, representing the view to the rear, darkened suddenly, but he kept his attention ahead. If there was anything really important aft, someone would tell him, though he hoped they wouldn’t before he was stopped. For an instant he wished he were actually riding the jet, so that he could feel when touchdown occurred.
But he knew anyway. The accelerometer and three human voices supplied the knowledge simultaneously. He stopped reaction mass flow and quenched the plasma fires almost completely, but kept ready to use fractional rocket power on one side or the other if a swerve developed. Any yawing could roll the Oceanus onto its back, and it seemed most unlikely that whichever wing was underneath could take such treatment.
“You’re down!” came Ginger’s voice, this time separate from the others. Belvew snorted faintly, and spared enough of his attention to utter a bit of doggerel which had survived in various forms from the time of fabric-covered aircraft.
“A basic rule of fliers, and all who’ve ever hopped: a ship is never landed until it’s really stopped.”
But deceleration was now rapid as the keel friction made itself felt, and a quarter minute later the landing was complete. Belvew knew he wouldn’t feel it, but his stomach tightened up anyway for several more seconds as he watched screen and vertical motion meters for evidence that the ship was breaking through a crust.
Apparently it wasn’t, and at last he felt free to let his attention focus on the view aft.
The screen darkening was from a slowly spreading cloud of black smoke, its nearest edge well over a hundred meters astern. It could not, the pilot saw at once, have been produced by friction between his keels and the surface; his landing slide hadn’t started that far back, and his thermometers showed that the keels were at about a hundred and fifty kelvins. They were cooling, but not so rapidly as to suggest they had been hot enough to boil Titanian tar in the last few seconds.
Not that anyone really knew what temperature that would take, he reflected fleetingly.
More to the point, a fairly deep trough in the surface, starting just below the near side of the smoke cloud and extending as far back along his approach path as he could see, confirmed that whatever had happened to the surface had come before touchdown. The most obvious cause was the exhaust from his pipes.
The smoke was being borne very slowly away from him by the negligible wind. The trough, perhaps half a meter deep and ten or twelve wide, remained uniform as the receding cloud revealed more and more of it, extending down the slope of the convexity. The jet had come to rest almost exactly at the top of the bulge, it seemed; both pitch and roll axes r
ead within a degree or so of horizontal.
“If it’s a crust, it’s pretty thick,” Goodell remarked.
“Unless the jets melted their way down and just produced more of it,” rejoined Ginger.
“Could be.” Being human, Goodell liked his own idea better; being a scientist of rank, he knew that alternative hypotheses, however unlikely, should always be developed as early as possible in hope of maintaining objectivity. “Let’s get samples.”
Belvew had powered down the flight controls, except for those which might be needed for emergency takeoff, and could safely nod his head, not that anyone could see him from their quarantine compartments.
“All right, in a few minutes. Non-destructive examination first. I assume everything in sight’s been recorded; now let’s look.”
“Right.” Goodell’s voice was a fraction of a syllable ahead of the others. Belvew activated the short-focus viewers on the lower part of his fuselage, and allowed their images to take over the Aitoff screen as his friends above chose—no, not above, he reminded himself; he was above with them; another real-surroundings reminder must be due. No one, however, said anything for several minutes; the surface still resembled obsidian at every magnification available and at every point the viewers could reach. The depression seen from the air was now hidden by the curve of the hill ahead, even though they were looking from its top, and the nearest point of the track presumably made by the exhaust was too distant for a really good look.
“I guess we dig,” Pete said at last. Belvew nodded again, as uselessly as before, but operated more of his controls.
The object which dropped from between the keels might almost have been an egg-shaped piece of the surface itself, as far as texture went, about fifty centimeters in its longest dimension. Until it reached the ground, which took an annoyingly long two seconds or so in Titan’s gravity, it appeared totally featureless. When it did strike, it flattened on the bottom to keep from rolling, uncovered a variety of optical sensors on the top and sides, and extended handling and digging apparatus, coring tools, and locomotion equipment.
