Light-Lag

The hull of *Pelican* was forty-one degrees on the sunward face and minus one-forty on the shadow side, and had been for six days, which was the whole of the problem and none of the drama. Ilse Vanterpool sat in the left seat of the forward cabin with her boots hooked under the rail and read the radiator loop temperatures off the panel the way another person might read a clock in a waiting room — not because anything was expected to change, but because the numbers were there and reading them was the job.

Number one radiator: nominal. Number two radiator: nominal, running four degrees warmer than one because it always ran four degrees warmer than one, a matched-pair asymmetry that had been in the maintenance file since before Ilse flew the ship. The loops rejected the crew's heat and the electronics' heat and the small unrelenting heat of three bodies breathing in a can, and they did it the only way heat could be shed with no air outside to carry it off: they radiated it into the dark as infrared, off two panels whose area had been fixed by a fabricator's drawing years ago and could not be increased now by wanting it. On a slow leg with the reactor loafing and the drive cold, the margin was enormous. You could run the galley heater and the exercise bike and never notice. Ilse noticed anyway. Noticing was cheaper than the alternative.

The cabin smelled of itself. Six days of recycled air had the particular flatness of a scrubber bed near the end of its cycle — not foul, just used, the CO₂ pulled down but the volatiles accumulating, a faint compound of warm plastic and skin and the ghost of the last meal. Dai had changed the primary bed on day four and would change it again on day eight, and between those two events the air simply got tired in a way the crew stopped smelling by the second day and would smell violently the instant they cracked a fresh canister.

"Housekeeping," Dai Ruvalcaba said from the engineer's station, which was his way of announcing that he was going to read her a list she did not need to hear and that they would both pretend otherwise. "Potable tank at sixty-one percent. Grey tank at forty. We reclaim tonight or we're carrying it to the depot, and carrying it costs mass we're not being paid to carry."

"Reclaim tonight."

"Reclaiming tonight. Scrubber bed at sixty-two percent loading, still nominal, changing it on schedule not before. Number two radiator is four warm."

"Number two radiator is always four warm."

"I log it every watch," Dai said. "The day it stops being four warm I want the log to say it used to be four warm." He said this without looking up. It was the most Dai sentence available and Ilse let it stand.

This was the texture of a transit leg, and the texture was mostly nothing. The circuit was a low-Δv, refuelled, multi-leg course strung between refuelling depots, because anything else was economically impossible: you did not carry a race's worth of propellant, you carried a leg's worth and topped up, and the whole sport was arithmetic performed against the gaps between the depots. Between the gaps you coasted. You did not thrust for the joy of it. Every metre per second of velocity change came out of a tank you had paid to fill and could not refill until the next depot let you, and so the dominant physical fact of Ilse's working life was that most of it was spent doing nothing at very high speed while the ship's systems ticked over and the two radiators quietly dumped the day's heat into a sky that never warmed.

Bek came up through the deck hatch at the change of watch with his hair still flat on one side. Tomas Bekkers, second pilot, young enough that he had not yet learned to sleep through the reclaim pump, which ran with a groan conducted straight through the ship's structure into whatever you were touching — through the bunk frame, through the deck, through the seat rail into the backs of Ilse's knees. There was no air out there to carry the sound, so the ship carried it instead, every pump and valve and gimbal broadcasting itself through the aluminium into your bones. You learned the ship's noises the way you learned a house. Bek had not learned them yet. He would.

"Morning," Bek said, though there was no morning. "Anything?"

"Number two radiator is four warm," Dai said.

"It's always four warm."

"He knows," Ilse said.

The comms window opened at 14:20 ship-time, which was a fact about geometry rather than a fact about anyone wanting to talk to them. The relay chain — a string of transponder buoys strung down the length of the course, each one receiving traffic from its neighbours and passing it along — ran on a schedule set by antenna pointing and buffer capacity, and *Pelican*'s slot in that schedule came round every four hours and eleven minutes. You did not talk when you wanted to. You talked when the window came, and in between you wrote your traffic and queued it, and it sat in the outbox with a timestamp on it, aging, until the buoy could take it.

The thing a newcomer never quite believed until they had lived it was that the window did not buy you a conversation. It bought you an exchange of letters between people who were minutes apart at the speed of light. Whatever the league said to you when the window opened, it had said some minutes ago, to a version of you that had since stopped existing. Whatever you said back, they would read after you had moved on to something else. Ilse had flown the circuit long enough that she no longer experienced this as strange. She experienced it as the medium she worked in, the way a diver experiences water.

The queue came down in the order the buoy had it. Weather on the depot — which was to say the depot's thermal state and traffic backlog, there being no weather. A conjunction notice from the league's catalogue office: two tracked objects passing within a screening volume of *Pelican*'s plotted path in thirty-one hours, both large, both catalogued, both with an assessed miss distance that made the notice a formality. Ilse read it once. It was one of a dozen such notices a week, generated automatically, filed automatically, and it meant only that the two things the catalogue could see were not going to hit her. What the catalogue could not see was not in the notice, because a notice can only warn you about objects large enough to be tracked, and the objects large enough to be tracked were, by and large, not the ones that killed people. She read it once and let it go, the way you let go of a weather report for a town you were driving through.

Then the thing they had been waiting six days for. A traffic item, league letterhead, priority-flagged, addressed to *Pelican*, subject line: **Entry status — Vanterpool/Kell.**

"Soraya's going to want this," Bek said.

"Soraya's asleep," Ilse said, and read it.

The message was warm. They were all warm; the league did not employ people who were not warm. It regretted the delay. It confirmed that the entry committee had convened. It noted that the committee's deliberations had turned on a scheduling matter — a depot handover slot, the physical business of which crew got which fuelling window at which station on which day, the sport's real currency laid out as a queue — and that a determination had been reached. The message stated the determination clearly and without hedging. It gave a time.

Ilse read it twice and did not say anything, which was how the others learned it was not good.

"Well?" Bek said.

"They've entered us," Ilse said. "On the C schedule. The determination was made"— she checked the timestamp on the league's clock, then the buffer log, then did the arithmetic she had done ten thousand times —"call it four hours and forty minutes ago, their sending. Plus lag." She looked at the clock and did not enjoy what it told her. "The C schedule starts its qualifying leg at a periapsis window we can't make from here without spending to make it."

"How much?" This was Dai, already turning to the ledger.

"Wake Soraya."

Soraya Kell came up through the hatch pulling a jacket on over a sleep shirt, hair tied back with the elastic she kept on her wrist for exactly this, and she did not ask what was wrong because the fact of being woken off-watch told her that. She read the message on Ilse's panel, standing, one hand on the seat back, and Ilse watched her do the same triple-check of the clocks that Ilse had done, because that was the discipline and Soraya had the discipline.

"They sat on it for six days and then entered us on the schedule that costs us the most to make," Soraya said. It was not a complaint. It was a reading of the situation, flat, the way you read a gauge.

"Why the delay?" Bek asked. He asked it the way he asked everything, as a whole sentence, expecting an answer. "It's a scheduling matter. It says so. Scheduling matters take an afternoon. Why six days?"

"It doesn't say," Ilse said.

"I know it doesn't say. I'm asking why."

"It doesn't say, Bek."

Bek looked at the message as though he could make it say more by wanting it to. There was nothing more in it. The message was complete, accurate, and exactly the shape of every message the league sent — it told you the outcome and not the reasoning, because the reasoning had happened in a room the message did not describe, four hours and forty minutes and some light-lag ago, to people who by now had gone home. You could ask. Bek would ask; his question would queue in the outbox with a timestamp on it; the window would come round in four hours; the answer, if it came, would describe a room that had emptied and a committee that had adjourned and would tell him nothing except that the outcome was still the outcome. Ilse had watched newer pilots than Bek burn a whole transit like that, sending clarification requests into the lag, each answer arriving warm and precise and useless, until they understood that the question they were really asking — *why did you do this to me* — was not a question the machinery could hold.

"Numbers," Soraya said to Dai, and sat down in the empty seat, and this was the part of the job that was actually the job.

Dai brought the ledger up on the centre panel and Ilse leaned in so the three of them could see it, and it was, like everything else, arithmetic. The ledger was a single conserved quantity written down: the total velocity change *Pelican* could still buy with the propellant in her tanks, given her mass, given the drive's exhaust velocity, given the pitiless logarithm that governed how much of that budget each manoeuvre spent. Delta-v. Spent and not recoverable. You could not slow down for free and get the fast back later; every number on the ledger came off the top and never went back.

"We're carrying nine hundred and six metres per second of usable budget," Dai said. "That's after reserve. The reserve is fifty for docking and contingency at the depot, which I am not touching and neither are you." He said the last to no one in particular and everyone understood it was to Soraya.

"Copy," Ilse said.

"To make the C-schedule periapsis window from here," Dai went on, and put a figure up, "the phasing burn is one hundred and thirty. That's the honest number, I've run it three times. It buys us the window. It does not buy us anything after the window."

"And if we don't make the window," Soraya said.

"Then we're not entered on any schedule, because the message says C or nothing, and we've spent six days and a depot slot getting here for a race we watch on the relay."

Nobody said anything for a moment. The reclaim pump chose that moment to start its cycle, and the groan came up through the deck and the seat rails and the backs of everyone's knees, and ran for its ninety seconds, and stopped, and in the quiet after it Ilse could hear the small tick of number two radiator's loop as it did its four-degrees-warm work in the dark.

"A hundred and thirty out of nine hundred and six," Soraya said, "leaves seven seventy-six. Minus the fifty reserve you're not letting me touch." She did the subtraction aloud because saying it made it a decision and not a wish. "Seven twenty-six of working budget to run the qualifying leg on a schedule that was designed for crews who arrived with a full tank and a fresh depot slot behind them. That is thin. That is racing on the reserve of somebody else's plan."

"It's thin," Dai agreed. "It's not impossible. It's thin."

Ilse said nothing, which Soraya heard.

"You don't like it," Soraya said.

"I don't dislike it," Ilse said. "It's a real hundred and thirty. It buys a real window. After that we race on what's left and it's less than I'd want and it's more than nothing." She turned the ledger with a finger so the reserve line was under her thumb. "Don't touch the fifty."

"I'm not touching the fifty."

Bek was still looking at the entry message when Dai made the noise. It was not a large noise. It was Dai clearing his throat in the specific way that meant he had found something in a log that did not close, and Ilse turned because that throat-clear had, over four seasons, never once been about nothing.

"Timestamps," Dai said.

"On what."

"On this." He had the relay buffer log open beside the entry message, the raw record of when each item had entered the buoy's buffer and when it had left. "The league sends the entry determination, and it's stamped at their clock, and I trust that stamp about as far as I trust any stamp. Fine. But the buffer log says the item entered this buoy's buffer stamped one thing and left stamped another, and the difference isn't the transit time. It's off. By a bit."

"By how much."

"Eleven seconds." He said it the way he said everything, dry, precise, a man reporting a reading. "The item is stamped as though it sat in the buffer eleven seconds less than the buffer's own clock says it did. Nominally that's the buffer rewriting the stamp when it re-queues — buffers do that, they re-timestamp on hand-off so the downstream clock stays consistent. It's a feature. It's in the spec." He paused, which for Dai was a whole sentence. "It's just that eleven seconds is a lot for a hand-off, is all. Usually it's under one."

Ilse looked at the number. Eleven seconds, on a message that had already aged four hours and forty minutes plus light-lag before it reached them, was nothing. It was less than nothing. It changed no decision, moved no window, cost no metre per second. The buffer had done a thing buffers were designed to do, a hand-off re-stamp, and had done it eleven seconds' worth instead of the usual one, which meant only that this buoy's buffer had been fuller than usual, or slower than usual, or that some upstream link in the chain had held the traffic a little and the buffer had absorbed the hold the way it was built to.

"It's the buffer," Ilse said.

"Nominally," Dai said. He held the word out and turned it over once, the way he did, and then he let it go, because there was nothing under it and both of them could see there was nothing under it. He logged it. He logged everything. The day it stopped being eleven seconds he wanted the log to say it used to be eleven seconds. He put it in the log with a note that read *buffer re-stamp, 11 s, hand-off, nominal* and moved on to the potable tank, and the clock on the wall went on keeping whatever time the relay chain had last agreed it should keep, and none of the four people in the cabin thought about it again that watch.

Soraya took the hundred and thirty.

She did not take it dramatically. She took it the way the sport was actually conducted, which was as a line in the ledger and a burn card on the panel and a callout to the crew. She had Dai confirm the mass and the phasing solution a fourth time, because a phasing burn to catch a periapsis window is not forgiving — you are trying to be in a particular place at a particular time relative to a gravity well, and the well does not wait, and the propellant does not come back — and Dai confirmed it, one hundred and thirty, honest number, three runs and now a fourth. She had Ilse fly it. Ilse flew it. The drive lit and the ship trembled with the specific whole-body shove of thrust, and the number two radiator loop's temperature climbed as the reactor came up off its loafing idle, and Dai watched the loops climb and stay inside the margin the fabricator's drawing had fixed for them years ago, and the burn ran to cutoff and the panel wrote one hundred and thirty-one against the plan's one hundred and thirty, close enough, a metre per second on the wrong side of the estimate and off the ledger forever.

Seven hundred and seventy-five. Minus the fifty Ilse would not let anyone touch.

"Seven twenty-five working," Soraya said, and wrote it down, and it was her hand that wrote it. "That's ours now. That's what we race on." She said *we*, and it was her decision, and everyone in the cabin knew both those things and left them alone.

The comms window would come round again at 18:31 ship-time. In the outbox, Bek's clarification request sat with a timestamp on it, aging, asking the league why six days, and it would go up when the window came and arrive when it arrived and be read by someone in a room that had emptied. Ilse looked at the course plot with the periapsis window on it now safely inside their reach, bought and paid for, and she looked at the working budget under it, thin, and she found that she was not uneasy, because the numbers were honest and the call was correct and the ship was warm and the radiators were nominal, number one nominal and number two four warm as it had always been.

That was the whole of it. A correct decision, made with the information available, written in Soraya's hand. Ilse had no way of knowing, sitting there with her boots hooked under the rail, that this was the shape every disaster in the coming season would take, or that she had just watched the first one and had, correctly, called it nothing.