The Far Shore

by Glenn Damato

  Eric’s red-eyed image comes on vid. Ryder asks, “Did you know the whole nav program is on override?”

  “Of course I do. I shut the TMP down because it was throwing out inconsistent data and I didn’t want to risk that it would fire the thrusters and deviate from our course.”

  I pull myself closer to the panel so Eric can see me. “So the nav program is defective?”

  “I didn’t say that. Once again, there are errors yet to be analyzed. Until we understand the errors, I shut the program down as a precaution.”

  Ryder jostles against me and leans directly into Eric’s vid, “You don’t trust the nav system?”

  Eric peers offscreen, as if watching someone out of view. “Darien knows the system better than me. Our initial TMP burn was perfect. That makes these errors hard to fathom. Until we understand what’s going on, we’re better off just letting the laws of gravitational trajectories keep us going in the right direction.”

  That’s not good enough. “Let’s get all the flight directors together, and Darien too, so we can figure out what to do. And Eric, are you looking into the OGS failures? We’ve been trying to understand what’s happening since breakfast.”

  “Oxygen production is down only five percent off nominal. I’m going to edit everybody’s tumble axis so the units spend more time in the shade, and that’ll cool them down.”

  Mikki thrusts her body between mine and Eric’s vid. “What happens if they crap out? We suffocate? They couldn’t give us a supply of liquid oxygen?”

  Eric shakes his head. “Too heavy once insulation and boil-off are factored. Compromises were made in order to maximize total payload to the surface. There wasn’t any way to test the whole configuration in actual freefall.”

  I think the nav problem takes priority. One more question. “The GNC has an internal clock, right? Would that create these errors? Could this be related to the clock synchronization problem? Earth seconds versus Mars seconds?”

  “No, because the GNC and the TMP always use Mars time. That’s what caused the bug with the thruster acceleration sensors.”

  Ryder twists my sleeve. “What you said makes sense.”

  “Does it earn me an engineering certification?”

  He laughs. “No, but I should have thought of it first. I’m impressed.”

  Peen!

  ◆◆◆

  Alison doesn’t doze off once all day. I’m supposed to be the sergeant, so I assign her and Shuko the learning modules covering the theory, maintenance, and repair of the carbon dioxide scrubbers and the Sabatier reaction equipment. She finishes all four related exams.

  “You got perfect scores,” I tell her. “That’s a lot of material to absorb.”

  Her pale blue eyes shine. “If Jürgen sees my scores, I may have a shot for the first Discovery Team.”

  Jürgen, the motivator. How did he develop that talent?

  Eric’s idea to cool the oxygen generators actually works. No high electrolyte temperature shutdown warnings since noon, and a single unit runs in primary mode.

  But I can’t get the TMP situation out of my head.. We had a perfect flight path. Now it’s throwing errors? The documentation covers the nav panel interface with minimal detail on how the overall system works. Optical devices mounted on the TMI stage continuously sight celestial objects in order to derive our current position and velocity. The GNC—Guidance and Navigation Computer—is supposed to feed that data to the TMP so it can follow a narrow flight path that ends on first contact with the Mars atmosphere. The precise position, velocity, and time of atmosphere contact are critical.

  The manuals say the GNC can run in simulation mode even with the Trans Mars Program in override. Why not try it? I make the request and the nav panel confirms and displays FIXING POS-VEL for a long minute, then TMP INITIATED, then, in red,

  PM1 UNAVAILABLE

  There’s the stomach flutter, again.

  PM1 is the term for our landing zone at Protonilus Mensae. What does it mean, unavailable? Can’t be anything good. I pull myself across the control center to my sleeper. The instant I’m closed within the privacy of my bunk, I get Eric to come on vid. His eyes are now completely bloodshot, exactly like launch day.

  “I put the GNC in sim mode,” I inform him. “PM one unavailable?”

  “It’s simple,” he answers. “That means we can’t land on Mars.”

  TWENTY-ONE

  I release two short, sharp breaths. “Eric! How the hell could that be?”

  “Because the guidance system is lost!” he yells back. “It has no idea where we are! And maybe never did!”

  “Darien agrees with this? Wasn’t he checking?”

  “Darien’s sleeping.”

  “Get him up!”

  “Don’t tell me what to do, okay? He’s asleep because there’s nothing more he can check. He doesn’t have the precision data to determine our true position.”

  “You have no plan at all?”

  Eric squints at me. “Something malfunctioned with the GNC internal system clock. The whole ephemeris is useless. You suggested this might be related to the clock sync problem that caused the thrusters to shut down. I take back what I said earlier. You may be correct.”

  “We know for a fact this is caused by the second-length discrepancy?”

  He rubs his eyes and takes a long time to answer. “No, we don’t know that, not for a fact.”

  “Explain what you do know. Explain in English, because my brain is tired.”

  Another long pause. “The guidance computer has an extremely accurate built-in clock. It generates a time signal, basically a number that represents how many millisecs, thousandths of a second, have elapsed since the system first activated three weeks ago. The Trans Mars Program needs this time signal input to calculate our position and velocity accurately. Our flight path needs to be precise enough so we hit the edge of the Mars atmosphere at just the right angle.”

  “And what’s that other thing? The ephemeris?”

  “The ephemeris is like a database that knows the position of the Earth, the sun, and Mars in the future. The guidance computer derives our position and velocity by comparing the time signal with the relative positions of Mars or the Earth against a set of navigation stars.”

  “It uses the star trackers to get the relative position angle against the stars?”

  “Correct. And you know what, Cristina? As of early this morning, the time signal . . . failed. It’s all wrong. It’s useless, which means the ephemeris is useless, which means the TMP has no idea where we are and won’t ever again know where we are!”

  “We know the nature of the beast. That’s the first step toward a solution.”

  Eric just worked himself into a panic, again. His face is red and tiny bits of sweat fly off in different directions with every word. “You don’t get it. We have no time signal. It won’t work at all without that precise time input. We can’t navigate.”

  “We find a way to produce our own time signal and feed that into the GNC.”

  “Cristina, if that were possible, I’d have done it by now.”

  “We’ll find a way.”

  “Yeah, well, Jürgen reached a decision.”

  I pull my face closer to the vid screen. What does Jürgen have to do with any of this?

  “Jürgen decided we’re going to keep the trajectory we have,” he continues. “Which, by the way, was nearly perfect when the TMP knew our position. The day before we land the GNC can optically range the Mars surface and derive our precise position and velocity so the TMP can do course corrections.”

  This is too much. “Jürgen decided, did he?”

  “He did. Now get some sleep, Cristina.”

  “Jürgen’s a geologist. Since when did he become a systems expert? Don’t you and Darien know more than he does? We’re wasting time! Show me these error messages. Get every engineer on the com right now, anyone who can contribute. To hell with Jürgen.”

  ◆◆◆

  The thin
walls of the sleeper didn’t muffle the conversation much. They know. Ryder has his arms around Mikki and Alison. Paige is wedged up against a window, arms folded, staring out into the blackness. Shuko peeks from his usual perch in the equipment bay, pale face framed by the access hatch.

  I say to no one in particular, “So yeah, we have a problem.”

  “If we’re going to die, tell us,” Alison says, voice cracking and childlike. “I can’t stand not knowing.”

  “Quit worrying, get back to studying,” I growl at her, way too harsh. It’s natural for her to wonder if studying or anything else matters anymore.

  Vids activate across the main panel. Eric, Tess, and two other faces unfamiliar to me, both with Indian features. Have to start learning people’s names.

  But no Jürgen. Fine.

  No one wants to speak first, so I begin. “Our guidance system doesn’t have a time input, and without that it’s lost. Eric, can you show us the error message?”

  We squint to read the letters, Ryder resting his chin on my left shoulder.

  60335 ALL DATUM OUT OF RANGE

  I ask, “How do we know that’s related to the time signal?”

  “The ephemeris tells the guidance system where Mars and Earth should be, relative to the background stars, in order to hold our planned course. The GNC is looking at the time signal, and looking at Mars and Earth against the background stars, and nothing makes sense. It’s impossible to calculate our position and velocity.”

  “You told me there is no time signal.”

  “I told you it’s failed, it’s wrong.”

  “But we do have a time signal of some kind?”

  “It’s wrong.”

  “Let’s see it.”

  Eric flicks the display to our vids. It’s a big number and doesn’t look anything like a time. Seven digits, the last one increasing every second, plus three more digits to the right of the decimal place changing too fast to read. The first two digits are zeros. The total number of seconds since restart is fifty-five thousand something. Do the math, that’s fifteen hours.

  Eric’s voice is more sleepy than agitated. “Basically it jumped backwards two billion milliseconds. It thinks it’s about twenty-four days ago. That’s why the positions of the planets can’t help us navigate anymore.”

  I watch the numbers change. “All of a sudden, it jumped backwards. For no reason?”

  “For no reason.”

  “Alright. So we generate another time signal, this one correct, and replace it.”

  “Not possible!” Eric responds. “It’s got to be precise to the millisec. No way to sync it.”

  The flight director on Resolute comes closer to his vid screen. He has a narrow face with dark, passionate eyes. “Pardon me, sir. I am Vijay Mehta and my knowledge of space navigation is nonexistent. Tell us why we cannot sync it.”

  “Because we would have to know the exact standard time the ephemeris requires. An error of a few thousandths of a second would kill us.”

  Vijay has another good question ready. “How did it get synchronized to start with?”

  “With the time signal from BeiDou, Harmony’s space nav system.”

  “Can we re-sync the same way?”

  Eric sighs. “We’re over four million kilometers out. BeiDou doesn’t reach this far. And if it did, we have no way of correcting the speed of light delay. No human being has ever been past the moon. We got a self-contained celestial navigation system. Once time synched, it doesn’t need BeiDou anymore.”

  I don’t know what else he’s saying because I’m doing more math in my head.

  “Eric!”

  He shuts up. Everyone stares at me.

  “You said the whole guidance system first activated three weeks ago—is that what you said?”

  “About three weeks, yeah, because we tried to test as much as we could before the rockets were printed.”

  “And it’s been running since then?”

  “Perfectly, and then it failed today.”

  “So when it failed, when it failed . . .”

  I can barely think. I’m trying to do the head math and talk at the same time. It’s got to be one or the other. I close my eyes and there are the numbers.

  Ryder rubs my shoulder.

  “So when it failed, it jumped back to time zero, the instant it first synchronized with BeiDou?”

  “It rolled back. To zero, yes. And it’s not supposed to do that.”

  “These systems, they were used to guide spacecraft to and from the lunar villages. That takes, what, a couple of days? So no one ever ran this equipment continuously for three weeks.”

  “I don’t see what difference that makes, Cristina. It should work forever. Self-contained celestial navigation computers have been guiding robot probes to the planets for a hundred years. Those trips lasted months, years!”

  He said it should work forever.

  No, it won’t.

  I scream the words, way too loud. Because I’m tired. “It can’t run forever, Eric! It runs for two billion millisecs and that’s the end!”

  Eric blinks. “What are you talking about?”

  “Look at the numbers! Do the math! It’s been fifteen hours and eight digits are taken up already. It can’t go beyond two billion millisecs—it runs out of digits! That’s a little more than twenty-four days. After another twenty-four days it’ll reset all over.”

  “Maybe you solved the puzzle,” Tess says. “But that does us no good whatsoever. The time signal is still wrong.”

  “It’s behind by the exact maximum value that can be stored in a ten-digit number.”

  “It’s a thirty-two bit signed integer, Cristina. But Tess is right. Even if you’ve solved the puzzle, we can’t kill the signal and replace it with another and then do the same thing in three weeks. It’d be off by a wide margin. Letting the TMP navigate with an incorrect time signal would be far worse than the prudent action, which is to keep the flight path we have now.”

  Ryder’s mouth is centimeters from my ear and his voice makes me jump.

  “But if we could replace the bad time signal with a correct signal, that would fix the whole mess for sure, right?”

  “No, not right. You’d still need a signal optimizer that accepts the time as an unsigned integer, and we don’t have one.”

  This is a start. “Signal optimizer? Speak English!”

  Eric’s face is replaced by a diagram of the Trans-Mars Injection stage, the fifteen-meter cylinder that supplies propulsion, power, water, and oxygen to each spacecraft all the way to Mars. A green pointer moves toward a round protrusion on the outer skin of the TMI.

  “These are high-precision star trackers, a kind of sextant, three of them, a hundred and twenty degrees apart. They take continuous bearings to measure the angular separation between the Earth, Mars, the sun, and stars like Canopus and Vega. That data is fed into this device here.” The pointer moves to indicate a box. “That’s the brains of the system, the trajectory signal optimizer that derives our position in space to within one hundred meters, fifty times per second. That’s the input to the GNC.”

  I enlarge the diagram. “We can’t fix this because we can’t reach it?”

  “It would be difficult to access it physically,” Eric says. “But that wouldn’t do us any good. The problem is still the ephemeris. The ephemeris was hard-coded into the optimizer the day it was printed and it cannot be changed. That’s a safety feature in case of power loss. And it accepts only a signed, thirty-two bit integer as the time signal.”

  A ruffle from behind me. Mikki pushes away from Ryder’s arm and twists around. She ducks into her sleeper and slides the door shut. She’s heard enough.

  I ask, “This optimizer, do we have the pattern so we can print a duplicate?”

  Eric’s irritated face fills the vid. “I just explained to you—the ephemeris epoch uses a standard time format and it wouldn’t work any better than what we already have.”

  “Can we edit the design?” The
question was from the flight director of Endurance, a woman with a stern and impatient face that matches her voice tone. Her hair is longer than everyone else’s and styled in a neat bun. Did she refuse the shipboard haircut?

  Eric clinches his eyes shut. “That would be an enormous risk, Senuri. The sensible option is to follow Jürgen’s decision and keep the course we have now.”

  I bang my palm against the screen. “Jürgen can’t do math! And he’s ignoring the fact we’re supposed to have at least two mid-course corrections during the flight. We’ll edit the logic to accept the different format and print another star tracker, then link it directly to the GNC. Eric, Vijay, Senuri, find out who can run your printers. We need a software engineer to modify the optimizer straight from the pattern.”

  Tess comes back, pout more pouted than usual. “Jürgen has to approve this.”

  I snap at her, “Why is that? Where is he now? Who appointed him supreme leader, by the way?” I turn to Alison. “How soon can you get one of our printers set up? Paige and Shuko can help you.”

  Eric snarls, “Cristina, do you realize this new tracker needs to be mounted outside? As in, outside the airlock, in vacuum? Pointing it out a window won’t work because optical refraction will distort the sight angles.”

  Ryder asks, “Can we design and print a bot to go out the airlock and mount the tracker?”

  “There’s no time.” I grab Ryder’s upper arm. “Every hour could mean more propellent required to get back on course. No more delays! We need to configure a BioSuit right away.”

  That draws a grin. “I get to go out the airlock?”

  Shuko shakes his head. Do I really want to trust Ryder outside the airlock?

  “Not necessarily,” I sputter. “You get my suit ready. I’m flight director. I’m doing this, just me.”

  But Jessica Egan on Resolute is an expert on the BioSuits and she nixes my plan. She calls me to her vid. Jessica’s face has one of those permanent little smile looks, but her tone is firm. “As a rule, two are safer than one. Especially since the airlock is not designed for use in flight.”