Aftermath

by Charles Sheffield

  "We'll discuss software and other possible causes later," Celine said curtly. "I don't want to talk about it now. Wilmer?"

  She turned to him, without much hope of hearing anything useful. It wasn't clear that he had even been listening. While Jenny and Reza were talking he had made a peculiar little drawing, and now he was scribbling numbers.

  "Oh, it wasn't the software." Wilmer grinned like an idiot. "At least, it was, but not at all in the sense that Jenny means." And then, while Celine glared, he went on, "Do you remember when we first noticed Supernova Alpha, you asked me what else it might do to the solar system? And I said, pretty much nothing, apart from melting ice for a while on the moons of the outer planets."

  "I remember." With anyone but Wilmer, you would bat them over the head if they chose such an awful time to wander way off the subject. With Wilmer you waited. His digressions always came back to the point.

  "Well, I was wrong," he said. "Stupidly wrong. Wrong in a way that anyone with a year or two of elementary physics could point out." He turned the sheet, so that they could see his drawing. It was of three concentric circles, with arrows pointing out from the second one toward the outermost. "We all know the pressure/volume/temperature relation for an ideal gas, Pv = RT. A planetary atmosphere satisfies that, almost perfectly. Increase the temperature and leave the pressure the same, and the volume increases linearly. Here's Earth's surface." He pointed to the inner circle. "Above it lies the atmosphere. Pump in heat, an incredible amount of it, from Supernova Alpha. For a couple of months it's like having two suns in the sky. The temperature of the surface rises. The atmosphere expands. Where does it go? The only place it can go." He pointed at the arrows between the second and third circle. "Upward. The whole atmosphere swells."

  Wilmer released the sheet of paper with the diagram, and it hovered before him in the free-fall environment of the Schiaparelli's cabin. "That's a general comment, but it's easy to catalog specific effects. First, there will be only a small change at ground level. The atmosphere has expanded, but its total mass remains constant. The surface will experience the same atmospheric pressure, because the whole column of air above it exerts the same downward force.

  "But now think about conditions higher up. The atmosphere still becomes thinner with height, but it does so more slowly than it used to. So if you go high enough, the air is more dense than it was at that same height before Supernova Alpha. The drag force and frictional heating on a spacecraft will increase—and they have an exponential dependence on air density.

  "The routines that we put into Lewis came from the general software library applicable to our class of orbiters. They provide an explicit calculation for drag force as a function of height, in terms of spacecraft angle of attack, mass, shape, and velocity—and air density. But it's the air density at a given height as it was before Supernova Alpha—not as it is now—that's in the equations. An acceptable angle of attack for a ship fifty miles up, moving through the atmosphere as it was two months ago, would be an absolute disaster today. No orbiter could stand the increased drag and heating. We saw what it did to the Lewis."

  Wilmer had credibility and authority on all matters scientific. He also spoke as though what he said was no more than common sense, and quite undeniable. Celine reminded herself that it was the unquestioned acceptance of authority—Zoe's authority, as head of the expedition—which had led her to remain silent before. She could not afford to do it again.

  "You may be right, Wilmer. But you may be wrong." And when he stared at her in surprise—this wasn't the old Celine—she went on, "Jenny may be right, there was an error in the way the software was transferred, so Zoe's action drove the controls the wrong way. Or Reza could be right, it was pilot error on Zoe's part that destroyed the Lewis. The trouble is, we have no way of knowing which idea is correct. Even if you are right, there's nothing we can do to prove it."

  "Oh, but there is." One nice thing about Wilmer, he was too intellectually secure to become upset when he was questioned. He rubbed at the top of his head and went on, "We lost radio telemetry for the critical period, but we have a complete visual record from the Schiaparelli's big scope. That provides our observables. We can compute trajectories using a variety of different assumptions—that the angle of attack was adjusted the wrong way, or that it was reduced but the drag was already too high for that to help, or any other idea that anyone has. The right model is the one which minimizes residuals between computer and observed values. We can even use the difference between computed and observed data to calculate a density function for today's atmosphere, one that best matches a computed orbit to the observations. I'm sure Jenny can handle that."

  "Jenny?" Celine looked uncertainly to Jenny Kopal.

  "Easily." Jenny nodded. She seemed like a woman reprieved from a death sentence. "It's a nonlinear least squares fitting problem, but we have all the routines."

  "So let's do it." Celine was about to add, Soon, so we can get out of here and down to Earth. But she was learning. "Take as much time as you need. You tell me when you're done. Then we'll discuss what comes next."

  * * *

  You could force patience on yourself and everyone else, but no one said you had to like it.

  Celine watched Jenny working for a few minutes, with Wilmer sitting by to assist if and when needed. Then she left the control cabin and wandered away to the Schiaparelli's observation chamber. She had another mystery to ponder.

  Zoe had been the leader of the Mars expedition. Ludwig Holter had been second in command. No backup to those two had ever been mentioned. Oversight, or deliberate act by the selection committee?

  Now Zoe and Ludwig were dead. And Celine, without making any conscious decision, seemed to have taken over the direction of the surviving group. Did she want to do that? Or, inverting the question, did she have any choice?

  Celine stared out at Earth, its surface again shrouded in night. The radio silence continued, broken only by weak and sporadic signals that addressed purely local problems of food, water, and power supply. The old Earth had been a celestial beacon, a roar of radio and television signals easily picked up when the Schiaparelli was orbiting Mars. That had gone. The firefly glow of light from the big cities was no longer visible. In its place she saw the ruddy sparks of bush fires across much of sub-Saharan Africa.

  The planet to which she so much wanted to return was nothing like the world that they had left. If they survived to land on it, they would find a tougher, wilder place.

  First, though, they had to live through the descent. Who would make the crucial decisions in the hours ahead? Put like that, the question of leadership became clear. She did not trust Wilmer or Jenny to direct the group. She wasn't sure she trusted Reza to do much at all, he was showing increasing signs of strangeness. And there was no one else.

  Celine left the observation chamber and headed for the control room where the others were working. True, she did not wholly trust herself. But maybe Zoe Nash, for all her apparent confidence and certainty, had felt the same way.

  Uneasy lies the head.

  The important question wasn't whether or not you thought you were the right one to lead. It was whether others believed you were.

  * * *

  What am I? What is my function?

  Celine, squeezed into the improvised hammock between Wilmer and Jenny and facing away from the front of the orbiter, felt a new wave of uncertainty rising within her. Reza sat behind them at the controls. Celine didn't like that, but she had no choice. He was by far the best pilot. She could see his distorted image in the shiny rear panel, singing to himself. Unless she told him to abort in the next sixty seconds, the Clark would leave the safe haven of ISS-2 and begin reentry.

  She had performed none of the data analysis and modeling that proved Wilmer's assertion was correct. That work had been done by Jenny and by Wilmer himself. It showed that the crew of the Lewis had died not because of pilot ineptitude or software transfer error, but because the equations embedded in
the control programs no longer modeled correctly the atmosphere of today's Earth.

  She had not changed the software, to incorporate the parameters of the new atmosphere determined by the data analysis. That had been Jenny's work.

  Nor would she fly the Clark back home. That responsibility lay with Reza, now well into manic mood.

  What, then, did she do?

  She worried, when apparently no one else did. The others were completely confident that the problem that killed Zoe and the rest of the Lewis crew had been solved. As Reza cheerfully said, "Everything else was on the button, exactly the way it should have been. We've cleared up the only problem." Yet it was his partner, Jenny, who in another context had assured the group that test a program as you liked, it always had one bug left. And she and Reza apparently didn't realize that "program" was a general term, applying just as well to a return from orbit as to a computer subroutine.

  Celine wondered how much longer she would have delayed the attempt to return to Earth, without Reza's remark the previous day: "The log shows this orbiter's past due for maintenance. There's a steady deterioration in condition, even when it's not being used."

  Reza's reflection was staring at her. Apparently the sixty-second grace period had expired. It was now, or abort to a later time. Celine nodded. "Do it."

  The thrust of the engines in front of her was silent and easy, apparently too gentle to affect their situation. It was surprising to watch the Schiaparelli and ISS-2 sail away ahead, continuing in their shared orbit. The orbiter had taken the first step, braking its motion enough to allow the trajectory of Clark to intersect the upper atmosphere.

  Now it was simply waiting. But not for long. In less than fifteen minutes they would know if the drag calculation had been the only problem affecting the Lewis.

  No one was wearing a suit. Celine had wanted that as a precaution against the failure of cabin integrity and loss of air. Two minutes of direct experiment ruled it out. Even without suits they could barely squeeze into the Clark's limited cabin space. With suits, forget it. The pilot might fly home, but no one else would fit in with him.

  "Everything is nominal," Reza announced. "The control routines are doing exactly what we hoped. We are losing altitude as planned and are already experiencing some atmospheric drag."

  He seemed without a care in the world, but his words made Celine think of Zoe. She had said almost exactly the same thing, shortly before the Lewis disintegrated to its individual atoms.

  "Do the drag forces seem to be following the new model?" Celine was being pushed back into the hammock, harder and sooner than she expected. She had to ask if things were all right, even though there was nothing she could do if she didn't like Reza's answer.

  "The new model works fine," Reza replied. His attitude didn't tell her anything. He sounded ready to fly a ship through the gates of hell. "We're coming down by the book. Trust crazy Reza. I think I could squeeze us a degree or two farther north if you want. It may be clearer there."

  "What's the cloud situation?"

  It was another problem, predictable but irritating. Normally the weather reports for a returning orbiter were provided by ground control, with access to metsat and to ground radar data. The Clark was forced to fly without any such aids. Reza was the only person on board who could see anything outside the ship.

  "Continuous cloud cover below, cumulonimbus by the look of them. But we're a long way from touchdown. Drag is higher, skin temperature going up fast. Sit tight."

  There was no choice. Celine didn't need to be told about the drag forces, she was pressing harder and harder into the hammock. Wilmer, to her right, was rolling in on her a little. The hammock support was not quite centered—her own fault, that had been her job. But he was quite a load, especially under what already felt like two gees and more.

  "Hull temperature close to three thousand. We're pushing three gees and projecting more than five." Reza forced the words from compressed vocal cords. The ship's deceleration was still increasing. "If there's going to be unpleasantness, it will be right about here."

  Unpleasantness. A pilot's gift for understatement. Their bodies had spent most of the past year in free fall, and the year before that in a Mars gravity only forty percent of Earth's. Five gees was intolerable. Celine had trouble breathing, and she could hear beside her Jenny Kopal's painful grunts. Wilmer was a silent lump at her side. How much more? And how much longer? Only the thermal skin of the orbiter's cabin wall protected them from the white-hot inferno beyond.

  "Hull temperature thirty-three hundred." Reza's reporting of the instrument readings was barely intelligible. "Five and a half gees. Angle of attack holding steady. Rate of descent constant. Hang in there. I think we're through maximum drag."

  It didn't feel that way to Celine. But then the force pressing her into the hammock became perhaps a tiny bit less. Breathing was agony, but a reduced agony.

  "Hull temperature thirty-two hundred. Deceleration under four gees and falling. Rate of descent steady." Reza tried to shout in triumph, and managed a wheezy croak. "We're through the worst. We made it, guys. We've got lift. We're home."

  Home? Not quite. But the Clark was no longer skimming like a flung stone across the skies of Earth. Celine could tell that they were flying, descending fast but buoyed upward by aerodynamic lift from the air. She struggled upright and turned in the hammock to face Reza.

  "Where are we? Do you have any idea of our position and ground speed?"

  "Don't know yet." He turned to grin at her. "The micro-positioning circuit says thirty-eight north and eighty-two west, but I don't know how much we can trust it. Depends if the GPS satellites are alive. I'd like visuals, but it's nothing but clouds below. We're forty-one kilometers up, descent rate eighty meters a second, airspeed eleven hundred, heading nearly due east."

  Celine wanted to see for herself. So apparently did Jenny. As the deceleration dropped they started to crawl to the top of the hammock. At the same moment they realized that it was not feasible. They would change the mass balance of the little ship, but worse than that they would crowd Reza's access to the controls. The overloaded orbiter was too small to permit passenger movement.

  Celine strained upward for one moment above the edge of the hammock before she slid back to her old position. She glimpsed white clouds below and ahead, their rolling heads bright in western sunlight.

  "I guess we can forget about ground assistance and ground information." Reza was focused on the cloudscape ahead of the Clark. "The only way we'll learn conditions below is to look at them."

  He wasn't asking Celine, he was telling her. Did she want to second-guess him? She peered again over the edge of the hammock.

  Reza had increased the angle of descent. The ship was swooping fast toward the cloud tops. "Seven thousand meters. Let's hope the altimeter works with the changed atmosphere." As he spoke the ship dropped into the clouds.

  Ahead of the orbiter sat unchanging gray vapor. The ride became uncannily smooth. The ship might have been hanging motionless, except for the altimeter. Celine could see it in the diffuse light that permeated the cabin. Its display was flickering rapidly downward: six thousand—five thousand—four thousand.

  At thirty-eight hundred meters, when she was beginning to panic, the orbiter vibrated heavily and a moment later was racing across the broken floor of the cloud layer.

  Reza could see what lay below, but she could not. His low whistle did nothing to reassure her. "What is it?"

  "Snow. On the ground, everywhere. If it's deep we'll have problems landing. The orbiters aren't designed for that."

  "Snow. I thought we were at latitude thirty-eight degrees?"

  "That's what the instruments say."

  "But that puts us nearly as far south as Richmond, and it's almost April. There shouldn't be snow."

  "Hey. I didn't order it. I'm just telling you what we've got down there. And I don't like the idea of trying to land in it."

  "Do you see cleared areas?"


  "There was one patch of blacktop back there, looked like it could be a cleared runway. It's behind us now. And there's a big body of water ahead. It could be the James River or part of the Chesapeake Bay. Either way, it doesn't help—we can't land on water. We'd better take another look at what I saw, find out if we can land there."

  The Clark banked steeply. Celine didn't need to be told that they were losing altitude fast. When the engines were off, the orbiters had the glide ratio of a brick. Reza was conserving power for the final approach and landing, assuming he would find a place where that landing was possible. The orbiter circled, losing more height.

  "It's not a commercial airport." Reza giggled. "Not a military base, either. Not a highway. And not very big. But it's all we've got. Hold tight. I'll have to use the engines full throttle and bank at the same time to drop us in there."

  Celine slid back down the hammock, to settle between Wilmer and Jenny. You dreamed for a whole year of the triumphant return to Earth. Although you never discussed it or admitted that you ever had such thoughts, you rehearsed mentally the words to be spoken as you emerged from the lander. Those dreams and words did not cover the case where you swooped to a blighted Earth across a snow-covered landscape, in a crippled and jury-rigged orbiter.

  "We're very close," Reza said happily. "Ten seconds to touchdown. But we're moving too fast, and the strip we're landing on is shorter than I thought. Even with maximum retro-thrust we're going to overshoot the far end. Be prepared for something rough."

  After that warning, the first contact of the orbiter with the ground seemed soft as a kiss. Celine heard the hiss of landing wheels and felt a tremor as they raced along the surface. The retro-thrusters howled, and once more she was pushed deep into the hammock.

  "This is it," Reza said, and the orbiter shuddered and reared up onto its head. Celine felt one crushing moment of force. Then she was lying on her back, staring up at the cabin's rear wall. Wilmer was lying half on top of her, muttering and wriggling. "Reza?" she asked.