Chapter 4
The Signal
I pressed play.
Static.
Twenty-two years of static, more or less, in the gap between the last words I'd heard in English and this moment. Static in dreams. Static in the back of my head when I was teaching. Static was the sound of the distance between me and everyone I had ever known.
Then the static moved.
Not stopped. Moved. The way it does when there's a voice underneath, pushing against the noise floor, trying to get out.
A pulse. A rhythm. Then:
"—identify as United Earth Vessel Hail Mary Two—"
A man's voice. Mid-forties, maybe. Steady. A faint accent I couldn't place — something Mediterranean, or what was left of Mediterranean, after sixteen years of cruise and whatever had happened to Earth's languages in the meantime.
"—diplomatic and scientific mission to the Erid system, 40 Eridani A. Crew of ten. Departed Earth orbit approximately sixteen years ago Earth reference frame, twelve point eight years ship-time. Currently in cruise phase—"
The signal swam. Rocky's translator was doing its best, but the Doppler shift had stretched the audio like taffy, and the algorithms were working hard.
"—if this transmission reaches Erid, please pass the following to Dr. Ryland Grace, if he is alive—"
I closed my eyes.
"—you saved us. You saved all of us. We never stopped working. Earth survived. The grain came back. The ice is receding. There are children alive today who only know about the dimming as a story their grandparents tell them, and we owe that to you and the others. We owe that to you."
I did not move.
"—we are coming to thank you. We are coming to learn. We are bringing letters from the families of your crew. Yáo's wife is still alive. She is eighty-one and she wrote you something. Ilyukhina's brother. DuBois's daughter, who is older now than her father was when he died. They wanted you to have these in your hands."
Rocky's translator clicked, struggling.
"—we are also bringing the bridge. The buoy chain. We have been deploying communication relays the entire cruise — one every six months ship-time, more or less, depending on geometry. By the time we reach Erid, the chain will be complete. Sol to forty Eridani, end to end, every node powered by sequestered astrophage in sealed containment. Slow. Patient. Reliable. We didn't want the contact to end when this mission ended. We didn't want this to be the only ship that ever made the crossing."
He paused.
"—we wanted there to be a way to keep talking. Even if no one ever flies again."
I opened my eyes.
Rocky was very still beside me. He had translated the words about the buoys himself. He had understood them before I had. He had been doing astrophage math for as long as I had, and he had heard the same thing I'd just heard — that someone on Earth had figured out what to do with the last of the dying miracle. Not waste it on flight. Save it for staying in touch.
The voice on the recording continued.
"—our estimated arrival in the Erid system is—"
The signal collapsed into noise.
The audio reconstruction kept working, kept trying, kept failing. After a few seconds, the speaker came back, but the voice was different now. Older. A woman.
"—Dr. Grace. The man who just spoke is Captain Davies. He is a kind man and he believes the things he said, and they are true. I will add one thing he would not."
I leaned forward.
"—not everyone wanted to send this ship. Some of us believed it was sentimental. Foolish. A waste of fuel the species could not afford. I was one of those people. I lost the argument."
I almost smiled.
"—I lost it because we ran the numbers on what it cost humanity to forget the people who saved it. The math was unfavorable. So we are coming. We are coming because some debts are not optional. We are coming because the woman who would have sent this ship herself cannot, for reasons of her own making, and she asked me to make sure you knew that the choice to come was hers, even if the going is ours."
I sat very still.
"—she said to tell you: the grain came back. He should know that the grain came back."
I put my hands on the console.
"—end transmission. Hail Mary Two, out."
The waveform went flat.
I sat there for a long time.
Rocky did not speak. Rocky knew not to.
I thought about a woman I had met for what could not have been more than a few hours total, across a few briefings I half-remembered through the fog of pre-mission training. A woman who, the records suggested, had done unforgivable things to keep humanity alive. A woman whose name I had read in one of the data dumps Earth had transmitted in the first year after I arrived on Erid, in a list of people standing trial in The Hague.
She had sent this ship.
She had not put her name on it.
She had sent a message saying the grain came back, which was not a message about grain. It was a message about the field where my father grew up, in Iowa, which I had mentioned exactly once in a psychological screening interview, and which she had remembered, and which she had used now, sixteen years ago, to tell me that the message was really from her.
She had also, apparently, ordered the buoy chain built.
"Rocky," I said.
"Yes."
"The buoys."
"Yes."
"Sequestered astrophage. Sealed reservoirs. One in each node."
"Yes."
"How long would the power last."
He was quiet for a moment. Doing the math. Doing it more carefully than I could.
"With a few grams per buoy. Low duty cycle. Receive-only most of the time, brief transmissions—"
"How long."
"Tens of thousands of years. Possibly longer. The astrophage does not need to breed. It only needs to convert mass to energy. Which it does as long as it is alive. Which, in sealed containment, with no Taumoeba and no oxidative stress and no light to trigger reproductive cycles, may be very nearly forever."
I exhaled.
"They figured it out," I said.
"Yes."
"They knew astrophage was dying. They knew the flights would end. So they took the last of the good cells and they put them in buoys. They built a bridge with what was left."
"Yes."
"That's—"
I didn't finish the sentence. I didn't know how.
Rocky tapped one claw against the console. Gently.
"It is good engineering," he said.
It was. It was the best engineering I had ever heard of. It was the engineering of people who had understood the assignment.
I wiped my face with the back of my hand. I hadn't realized I'd been crying. The Eridian observatory is dry and cold and tears evaporate faster than they should, and I was grateful for it.
"Okay," I said. "Show me the ship."
Chapter 5
Hail Mary Two
Rocky brought up the schematic.
The Eridian deep-space array had been tracking the incoming vessel for three weeks before this morning. They hadn't told me. They hadn't wanted to tell me until they were sure. Eridians don't speculate. They confirm.
Hail Mary Two was beautiful.
That was the first thing. The original Hail Mary had been functional — a fuel tank with a habitat bolted to one end and a centrifuge bolted to the other, designed by people who had eighteen months and a dying sun and no time for elegance. Hail Mary Two had been built by people who had time. You could see it in the lines.
A long central spine. Maybe a hundred and forty meters, end to end. A rotating habitat ring two-thirds of the way down, big enough to spin up a full Earth gravity for the crew. Forward of the ring, a science module that looked, from the schematic, like someone had taken the Hermes and asked what if we did it again, but right this time. Aft of the ring, six segmented fuel reservoirs in a staggered arrangement.
A crew of ten. Awake the whole way. No coma pods.
"They learned," I said.
"Yes."
"They separated the fuel. Compartmentalized. So if one chamber goes bad—"
"The others survive."
"Yeah."
I looked at the schematic. Six separate astrophage reservoirs. Six separate chances. Six separate failure modes.
"How fast?"
Rocky brought up the velocity profile.
The Hail Mary One had cruised at about ninety-two percent of light speed. Hail Mary Two had pushed harder. Ninety-six. Ninety-seven at peak. Bigger ship, more fuel mass fraction, longer burn at higher acceleration. The result was that the crew had experienced about twelve and a half years of cruise time for sixteen years Earth-frame. The time dilation wasn't dramatic. But it was enough that they hadn't needed the coma. They'd built a life on that ship instead. Ten people awake, in a centrifuge habitat, going to a star.
I thought about that.
I thought about a crew small enough to know each other. Small enough that every face would matter when I met them. Small enough that I could carry their names home.
"Rocky."
"Yes."
"Show me the fuel."
He did not bring up the fuel data.
"Rocky."
"Yes."
"Show me the fuel."
He did. Slowly.
The model rendered on the screen. Six reservoirs, color-coded by viability. Three of them were green. Two of them were yellow. One was red.
"Define red," I said.
"Astrophage population in the chamber has dropped below replacement rate. Cause unconfirmed. Suspected Taumoeba contamination during pre-launch provisioning."
"How long ago did they figure out the chamber was bad?"
"Approximately nine Earth years ago. Mid-cruise."
I exhaled.
So they had known. For nine years they had known. They had crossed the gulf between stars with one of their six fuel tanks slowly dying, and they had not turned around, because by the time they noticed, turning around would have cost more fuel than continuing.
"And the yellow?"
"Population stable but reduced. Energy density below specification. Viability for braking burn uncertain."
I did the math in my head. I was slow at it. I was always slow at it. But I had been doing astrophage math for twenty-two years and I could do it without a calculator now.
Three good tanks. Two compromised. One dead.
Required delta-v to brake from cruise velocity into a stable Erid orbit: enormous. Specifically, the delta-v of the entire mission's worth of acceleration, applied in reverse.
I looked at the numbers.
I looked at them again.
I said, very quietly, "Rocky. They cannot stop."
"No."
"They are going to overshoot the Erid system."
"Yes."
"At ninety-plus percent of c."
"Yes."
"And they know this."
"Yes."
"And the message they sent—"
"Was sent before they would have known with certainty. Yes."
"But they would have suspected."
"Yes."
I sat back.
I thought about Captain Davies, mid-forties, steady voice, telling me Earth had survived and the grain had come back. I thought about him sitting in his command chair on a hundred-and-forty-meter ship, knowing that the math was probably not going to work, and saying it anyway: we are coming to thank you. Knowing that coming and arriving were not the same word.
I thought about the woman. About what she had not said.
She had not said save us.
She had said the choice to come was hers.
She had known. She had sent them anyway. Because some debts are not optional.
I put my head in my hands.
"Grace."
"Give me a minute."
He gave me a minute.
After a minute, I said, "What's the intercept geometry?"
Chapter 6
Why Humans Curve
Rocky brought up the geometry.
This is where my Eridian education paid off, or where it was going to have to.
The intercept problem is, in human terms, a tail chase. Hail Mary Two is moving very fast toward the Erid system on a trajectory that will carry it through the outer system and out the other side. We — meaning me and Rocky and whatever ship we can put together — need to launch from Erid, accelerate to match velocity, rendezvous, transfer the crew, and decelerate back to Erid.
In human terms, this is impossible.
The delta-v budget is absurd. You'd need to accelerate to nearly the cruise velocity of Hail Mary Two, then decelerate from it, then accelerate again to come home, then decelerate again to stop. Four full burns at relativistic velocity. The fuel mass required is more astrophage than exists in the Erid system.
In Eridian terms, the problem is different.
I had learned this slowly, over twenty-two years. I was still learning it. Eridian children grasped it at age three. The basic principle was something Threem-Threem had asked me about, only that morning: why do humans curve.
Humans curve because we evolved looking at thrown rocks and falling apples. Our intuition for motion is parabolic. Our spacecraft trajectories, even the most sophisticated ones, are recognizably arcs — Hohmann transfers, gravity assists, slingshot maneuvers. We shape our paths around gravity wells because gravity wells are where the free energy is.
Eridians evolved without sight. They navigate by sound and touch. Their cities are vertical. Their bodies are radially symmetric and built to grip. When they think about going somewhere, they don't think arc. They think anchor, tension, traverse, anchor. Their ships travel in straight lines between fixed points in space — what they call nodes — and they don't curve, because a spider doesn't curve along its web. A spider goes from one anchor to the next.
This is, from a human orbital mechanics perspective, deeply suboptimal. It throws away gravitational assists. It ignores energy-efficient trajectories. It treats space as a grid of points rather than a continuous field of potentials.
It is also, in this specific case, the only thing that might work.
"Walk me through it," I said.
He brought up the proposed intercept.
The Eridian model assumed a launch from the orbital tether at Kemu — which meant we'd start with the rotational velocity of the tether plus the orbital velocity of Erid around 40 Eridani A. Free delta-v. Several kilometers per second of it, gifted by physics. Humans usually launched from planetary surfaces and threw away that gift. Eridians had never made that mistake because Eridians had never been stupid enough to put a spaceport on a planet.
From the tether, the model showed a straight-line burn out of the Erid system at high acceleration. Not toward where Hail Mary Two would be when we arrived. Toward where Hail Mary Two was, right now, at the moment of launch. We'd burn toward an empty point in space, because by the time we got there, the empty point would not be empty anymore. The ship would arrive at the same time we did.
A node.
"This is the part I do not believe," I said.
"Which part."
"The fuel."
"Yes."
"You're showing me a model where we make this intercept with the fuel we have."
"Yes."
"And we don't have that fuel."
Rocky paused.
"No," he said. "We have it. We do not have it and the return."
I looked at the screen.
The Eridian model showed our hypothetical ship reaching Hail Mary Two with sixty percent of its fuel reserves intact. Enough to match velocity. Enough to dock. Enough to transfer crew.
Not enough to come home.
"Rocky."
"Yes."
"This is a one-way intercept."
"With the astrophage we have today, yes."
"What ship are we talking about, exactly."
He hesitated.
I already knew. I had known since the moment he'd started talking. But I needed him to say it.
"Rocky. What ship."
"The Hail Mary."
I closed my eyes.
"My Hail Mary."
"Yes. She has fuel. She has been maintained. Eridian engineering has improved many of her systems. She is the only human-built vessel in the Erid system. The incoming crew will know how to use her. They will know how to be in her."
"She's twenty-two years old."
"She is the ship we have."
"She's a fuel tank with a centrifuge."
"She is the fuel tank we have, Grace."
I opened my eyes.
The Hail Mary. My Hail Mary. The ship I had taken on gravity vacations for the last fifteen years. The ship I knew better than any human had ever known any spacecraft, because I had lived in her during the worst weeks of my life and the best weeks of my life, and I had spent the years since taking her apart and putting her back together for fun.
She still had her original astrophage reserves, mostly. Topped up over the years by the Eridian breeding facilities. Maintained. Cared for. Used.
She could make the intercept.
She could not make the return.
"Rocky."
"Yes."
"If we take the Hail Mary out to meet them—"
"Yes."
"—then we transfer their crew to her—"
"Yes."
"—she still does not have the fuel to brake back into the Erid system."
"No."
"So what is the plan."
He brought up another model.
A second ship. Eridian-built. A cargo brick. Launching from Kemu six days after the Hail Mary, on a different trajectory. Not to intercept Hail Mary Two. To intercept us, on our way back. A fuel tanker.
A refueling node.
A spider's anchor point, halfway home.
I looked at it.
"Rocky."
"Yes."
"The Eridian fuel reserves are dying too."
"Yes."
"Can the tanker carry enough."
"If we launch it within seventy days. Yes. Barely."
"And after that."
"After that, there is no more astrophage in the Erid system viable for relativistic flight. There may not be again. The breeding is failing. We do not know why. We have theories."
"What theories."
"Many. None confirmed."
I sat back.
I thought about a woman in a courtroom on Earth, sending a ship she would not name. I thought about Captain Davies, twelve years into a cruise, watching his fuel tanks die one by one and never turning around. I thought about Threem-Threem in my classroom, asking why humans curve. I thought about my father's field in Iowa, where the grain had come back.
I thought about the buoys.
The buoys, which would be powered by astrophage that the Hail Mary Two crew had set aside before the cruise — sequestered, sealed, protected. Untouched by whatever had contaminated the fuel tanks. Pristine cells, doing nothing, waiting in vacuum to be activated.
The miracle organism, dying everywhere else, alive in those small sealed reservoirs.
It would outlive all of us. It would outlive the species that made the buoys and the species that received them. It would still be ticking, still converting mass to energy, still pulsing signals across twenty-two light-years, long after everyone who remembered why it mattered was dust.
"Rocky."
"Yes."
"How many of them can we bring back."
"All of them. If the math holds. If the tanker arrives. If the Hail Mary holds together. If we are careful."
"That is a lot of ifs."
"Yes."
"Okay."
"Okay?"
"Okay. Let's go get them."
Rocky tapped one claw against the console.
"You are old, Grace."
"I know."
"Your heart."
"My heart is the best heart on this planet."
"Your heart is the only human heart on this planet."
"Same thing."
He made the sound that was either amusement or disapproval.
After twenty-two years I still couldn't always tell.
I had stopped trying.
Chapter 7
The Pedagogical Justification
The Eridian Council met that night.
I was not invited. I had never been invited to a Council meeting in twenty-two years on Erid, despite, you would think, having earned a chair. Eridians do not run their government by committee in the way humans understand committees. They run it by what Rocky once translated as the long conversation, which involves a small number of senior engineers reaching consensus through a process I have never fully understood and which seems to involve, among other things, a great deal of sitting in the dark together making thoughtful clicking sounds.
I waited at home.
Home was a small pressurized apartment on the third tier of Kemu, calibrated for a human — Earth-standard atmosphere, slightly lower temperature than the Eridian average, a single round window facing the ammonia flats. Twenty-two years of accumulated stuff. A bookshelf of Eridian-printed paper books, mostly mine — they'd reverse-engineered Earth printing for me as a gift in year three. A small kitchen I rarely used because Eridian engineering had eventually produced a passable approximation of pasta. A photograph of my brother, taken on the day I left for the Hail Mary, faded now, his face slightly out of focus because he had been laughing.
I sat in the chair by the window and waited.
Around midnight, Erid time, my watch buzzed.
It was Rocky.
"Grace."
"Yes."
"The Council has approved the mission."
"Okay."
"They have one condition."
"Of course they do."
He paused.
"You are not to go."
I sat up.
"What."
"The Council has decided that the risk of losing you is too great. You are the only human on Erid. You are a cultural and scientific asset of incalculable value. You are sixty-six years old. They have decided that the mission will proceed with an Eridian-only crew and a small contingent of trained pilots who have studied the Hail Mary's systems."
I stared at the window.
"Rocky."
"Yes."
"You're joking."
"I am not joking. I do not joke about Council decisions."
"You absolutely joke about Council decisions. You once described the Minister of Atmospheric Engineering as, and I quote, a respected colleague whose ideas are sometimes correct."
"That was not a joke. That was an accurate summary."
"Rocky."
"Yes."
"I am going."
He was quiet for a long moment.
Then he said, "I know."
"You know?"
"I told the Council you would not accept the decision. They asked me to convey it anyway. I am conveying it."
"Tell them no."
"I have told them no."
"Tell them no again."
"I have told them no four times. They have asked me to ask you formally one more time. The pedagogical justification, as your student would say, is that they want it on record that they tried."
I almost laughed.
"Tell them," I said, "that the pedagogical justification is that I said so."
There was a sound on the other end of the line. The sound that was either amusement or disapproval.
After twenty-two years I still couldn't always tell.
But this time, I thought, maybe I could.
