The alarm came on softly, the way it always did when the ship wanted attention without panic.
A change in pitch, barely noticeable unless you’d lived with it for months.

Lieutenant Harold Harrow noticed.

He floated for a moment, eyes closed, counting the seconds between tones. Three-point-two. That was wrong. Thermal regulation alarms cycled at four.

He pushed off the bulkhead and drifted to the engineering console.

The numbers were already bad.

Heat accumulation in the aft spine—slow, steady, and cumulative. Not an explosion risk. Worse. Waste heat had nowhere left to go. The primary radiators showed microfracturing along three panels, likely micrometeoroid damage worsened by dust adhesion from the last correction burn. The ship had been bleeding efficiency for weeks.

He ran the projection.

Then ran it again.

Core temperature would exceed tolerance in forty-seven hours.

Crew complement: thirty-six.

They were well past the turn-back point. Delta-v didn’t negotiate.

Harrow opened the shipwide channel.

“Engineering to command,” he said evenly. “We have a thermal failure.”

The captain arrived in six minutes, which meant she had already read the model.

“Options,” she said.

Harrow brought them up. “Automated purge of the aft exchangers buys twelve hours, maybe less. Manual realignment of the exterior radiator vanes restores full function.”

“And exposure?”

“Continuous EVA. Minimum six hours,” Harrow said. “Radiant load exceeds suit dissipation capacity. The cooling loop will saturate.”

She looked at the numbers herself, then back at him. “Meaning?”

“Suit temperature will rise. Coolant will boil off. Neural function degrades before cardiac failure,” he said. “There’s no recovery window.”

Silence settled into the compartment.

“That’s a death,” the captain said.

“Yes, ma’am.”

“Anyone else qualified?”

“No,” Harrow said. “I designed the system. I know where it misreports.”

She studied him for a long moment. No theatrics. Just arithmetic.

“I can’t order someone to do this,” she said.

“No,” Harrow agreed. “But I can tell you what happens if no one does.”

He expanded the thermal curve. “If we don’t restore radiator efficiency, internal temperature rises slowly. Symptoms appear late. By the time anyone realizes what’s happening, we lose cognition, then control, then the ship.”

He let that sit.

“If I go out,” he continued, “the system stabilizes. Mars gets a crew.”

The decision was made without ceremony.

Preparation was efficient. No speeches. No ritual. Harrow recorded a technical brief for the engineering team—what failed, what worked, what assumptions were wrong. He left no personal message. There was nothing operational to add.

The suit sealed around him, a closed system counting down from the moment it locked.

Outside, the ship’s skin radiated stored heat like a slow fire. The first hour passed without incident. By the second, the suit’s cooling loop was operating at maximum throughput. By the third, the alarms changed tone—not warnings now, but diagnostics.

Coolant temperature climbing.
Heat rejection insufficient.
Neural load advisory.

His hands began to lose fine control at hour four. He compensated by slowing down. Every adjustment mattered. Every degree reclaimed extended the crew’s margin.

At hour five, the suit’s internal temperature crossed the threshold for sustained cognitive impairment. Vision narrowed—not poetically, but mechanically. Peripheral data dropped out first. His breathing became shallow as the system diverted power from comfort to circulation.

He finished the final vane alignment by touch alone.

Inside the ship, the thermal graph flattened.

Then dropped.

The suit alarm shifted one last time, registering loss of motor coordination. Harrow acknowledged it out of habit, though the system no longer required confirmation. His core temperature continued to rise. Coolant reserves depleted completely.

Cardiac arrhythmia followed hypoxia.

Neural activity ceased thirty-two seconds later.

Inside the ship, his biometrics flatlined on the engineering display at the exact moment the aft spine returned to nominal operating temperature.

The captain waited for confirmation. She waited for redundancy.

“Engineering,” she said quietly. “Report.”

There was no answer.

Mars grew larger in the forward screens over the following weeks. The crew spoke less and checked their work more carefully. No one used Harrow’s name unless required for logs. The ship carried his absence the way it carried everything else—as accounted mass.

On approach day, the captain completed the final entry.

Thermal systems nominal. Transfer successful. One crewman remained at his post until the system no longer required him.

She closed the file and set the ship on course.

Mars filled the forward screens.