A hard sci-fi short set in the 22nd-century Sol system, where orbital mechanics leaves almost no room for mistakes.

The warning reached Mars nineteen minutes late.

By then, the freighter Kestrel had already crossed the point where no sane pilot touched the main engine.

Commander Ira Bae watched the alert scroll across her console in clean black text, stamped with Earth Standard and legal boilerplate:

SOLAR PARTICLE EVENT DETECTED. ESTIMATED PROTON FLUX EXCEEDS CREW LIMITS OUTSIDE SHELTER. SEEK RADIATION STORM PROTOCOL.

Nineteen minutes. The speed-of-light tax.

Outside the armored blister of her command deck, the Sun was still an ordinary white coin. No flare. No omen. Just numbers arriving late, as always.

“How bad?” she asked.

Kaito, her flight engineer, had already pulled up the heliophysics feed from Phobos relay.

“Class X9 equivalent,” he said. “Maybe higher. First arrivals in twelve minutes if the model holds.”

“Twelve from now, or twelve from when they detected it?”

“From now. We got lucky on geometry.”

Lucky. A word spacers used like prayer.

The Kestrel was two hundred thousand kilometers sunward of Mars, coasting on a transfer arc from the Ceres lanes. Its cargo bay carried thirty-eight tonnes of superconducting cable and isotope shielding, all under contract to Vallis City Grid Authority. Miss delivery by more than forty-eight hours and the penalties bit hard enough to bankrupt small operators.

Miss life support margins and penalties stopped mattering.

Ira toggled the trajectory display. Thin blue arc: planned coast. Green circle: Mars capture corridor. Red cone: exclusion zone around periapsis where any burn longer than seven seconds could throw them off capture and turn a freight run into a two-year solar orbit.

They were three minutes from that cone.

“Storm shelter status,” she said.

Nara answered from habitat section. “Water jackets topped. Med bay cots secured. We can fit all four in fourteen minutes if nobody argues.”

“No arguments,” Ira said.

She keyed shipwide audio. “Radiation protocol alpha. Nonessential crew to shelter. Kaito stays with me until transfer complete.”

The acknowledgement chime came fast. They had drilled this. Drills were cheap; physics was not.

Kaito expanded the propulsion panel. Their main drive was a closed-core fission thermal, old but brutally reliable, with hydrogen reaction mass and enough specific impulse to make accountants smile. In deep space it was a scalpel. Near periapsis it was a grenade.

“Option one,” he said. “Do nothing. Ride the storm in shelter. Keep nominal capture burn.”

“Dose?”

“If flux hits forecast, command deck gets fried to twenty sieverts in an hour. Shelter keeps us under point-three if we stay put.”

Point-three was survivable. Unpleasant, but survivable.

“Option two?”

“Pre-burn now. Raise periapsis by seventy kilometers. Buys us a wider burn window later. But…”

“But?”

“We need ninety-one seconds continuous thrust. We start now, we cross the red cone mid-burn. Guidance may still catch it, but if injector pressure dips, we miss Mars and we’re gone.”

Ira did not look away from the orbital plot.

Outside the hatch, she heard boots pounding through the access tunnel. Nara shepherding Tomas and little Deji, the cargo specialist, toward the shelter compartment wrapped in water tanks and food lockers.

The Sun remained polite and unchanged.

“Telemetry confidence on the flare?” Ira asked.

“Seventy-two percent,” Kaito said. “Could be lower, could be much worse.”

“Could be a false alarm.”

“In this line of work?” He gave a humorless laugh. “Sure. Could also be God with a magnifying glass.”

Nara’s face appeared on the internal feed, already strapped into shelter restraint.

“Commander,” she said, “hatch closes in five.”

Ira had made this decision before, years ago in cislunar traffic, when a tanker cracked a coolant line and she had to choose between docking schedule and lung tissue. She had chosen lungs. Nobody wrote songs about it.

She touched the console and drew a manual line from now to plus ninety-one seconds. Half of it ran through the red cone.

“No pre-burn,” she said. “We stay on nominal capture.”

Kaito stared one beat too long, then nodded.

“Copy.”

“Transmit decision to Mars Control. Include confidence and timing.”

“They’ll read it nineteen minutes after we’re done being relevant.”

“Send it anyway.”

He sent it.

Nara’s voice came again. “Hatch closes in ninety seconds.”

Ira killed noncritical panels and set automation for capture sequence. The ship could fly itself through the next hour if sensors survived. If they didn’t, there would be nobody left to complain about software design.

She and Kaito moved fast through the spine corridor. Metal rang under their boots. The Kestrel was built for mass efficiency, not comfort; every surface was either structure, propellant line, or cable run. At the shelter hatch, Nara hauled them inside and dogged the wheel shut.

The shelter smelled of plastic, sweat, and recycled air. Water tanks lined the walls, each one another centimeter between human tissue and charged particles.

Tomas, their medic, checked dosimeters clipped to each suit collar.

“Clock started,” he said.

No windows. No stars. Just the faint vibration of pumps and the distant whisper of the reactor through bulkheads.

For seven minutes nobody spoke.

Then every personal dosimeter beeped at once, sharp and high.

Tomas read first. “Outside flux spiking. Fast rise.”

Kaito exhaled through his teeth. “Forecast was right.”

Nara braced a hand on the hatch like she could feel radiation trying to get through. “How long?”

Tomas watched the graph crawl. “Peak in twenty. Maybe thirty.”

Ira forced herself to slow her breathing. Panic wasted oxygen.

In the dark she pictured the particle front crossing interplanetary space: protons accelerated near the Sun, threading magnetic fields, slamming into hull and circuitry. Ancient violence arriving as statistics.

The Kestrel rode it out.

At T plus forty-six minutes, the dose rate began to fall.

At T plus fifty-two, Mars Control finally replied to Ira’s transmission.

ACKNOWLEDGED. RECOMMEND SHELTER MAINTAINED UNTIL FLUX BELOW THRESHOLD. UPDATED CAPTURE SOLUTION ATTACHED.

Nineteen minutes late and exactly correct.

Kaito snorted. “Thanks, Mars.”

Ira opened the attachment anyway. They had recalculated a slightly longer capture burn to compensate for drag model updates in the upper atmosphere. Good work, even delayed.

“We use it,” she said.

When the flux dropped below threshold, they opened the hatch and moved back to stations. The command deck smelled faintly scorched. One auxiliary display was dead. Two external cameras were snowblind with sensor noise. But guidance was alive, nav solution stable.

Mars filled half the forward screen, rust and cloud bands turning slow under sunrise.

“Capture burn in three minutes,” Kaito said.

Ira strapped in.

“Engine injector?”

“Green.”

“Reactor?”

“Green.”

“RCS?”

“Green enough.”

Green enough. Another spacer prayer.

The timer hit zero.

The main drive lit with a deep mechanical roar transmitted through frame and teeth. Acceleration pressed them into couches. Numbers marched: velocity bleed, periapsis lock, target vector converging.

At fifty seconds, injector pressure fluttered.

Kaito’s hands moved before the alarm tone finished its first chirp, rerouting feed through backup valve B.

Pressure recovered.

At eighty-nine seconds, guidance called burn complete.

Mars captured them.

No applause. Just everyone checking numbers twice.

Tomas broke the silence first. “Dose totals?”

He read them out. All under emergency limits. No acute syndrome expected. Follow-up bloodwork mandatory for six months.

Deji laughed, too hard. “So we get to be old and irritable.”

“If the contract office doesn’t kill us first,” Nara said.

That got a real laugh.

They coasted into the high transfer lane above Mars, where traffic beacons blinked and tugboats waited like patient insects. Hours later, when the immediate checklists were done and the ship was officially someone else’s scheduling problem, Ira sat alone with a cup of bitter coffee and opened the message queue.

One new packet from Earth weather command, stamped almost an hour after the event began.

POST-EVENT ANALYSIS: PEAK FLUX EXCEEDED INITIAL FORECAST BY 18%. VESSELS OUTSIDE STORM SHELTER REPORT SEVERE CREW EXPOSURE. YOUR DECISION LOG REQUESTED FOR TRAINING ARCHIVE.

Ira stared at the line for a long time.

She could imagine the training module already: diagrams, timelines, maybe her voice if legal approved release. Students in orbit over Luna, in habitats under regolith, on ships leaving Jupiter’s Trojan yards, all learning the same old lesson in fresh formatting.

In the 22nd century, civilization had spread across the inner system. Mercury ran mirror farms. Venus floated cities in sulfur light. Mars exported software and stubbornness. Ceres brokered water and debt. Ships crossed millions of kilometers on schedules measured in synodic cycles and propellant fractions.

But nothing had changed about causality.

You still could not negotiate with light-speed delay.

You still could not outvote orbital mechanics.

And when the Sun spoke in charged particles, you still hid behind water, math, and whatever discipline you had left.

Ira opened a reply window and dictated the incident summary.

No heroics. No poetry. Just sequence, timing, thresholds, decisions.

At the end she added one personal line, then almost deleted it.

She left it in.

Recommendation: train crews to decide with incomplete truth. Full truth arrives late.

She hit send.

Nineteen minutes later, nobody important had read it yet.

That was fine. The message was in flight.