Kaelen’s first instinct was conduction. “Just sink the heat into the lunar regolith,” he muttered, flipping to Chapter 3. But the numbers were brutal: lunar soil was a poor conductor. The heat would build up faster than it could diffuse. The reactor’s silicon carbide housing would reach critical temperature in under an hour.

Radiation. His last hope. Kaelen stared at the Stefan–Boltzmann law in Chapter 12. In a vacuum, radiation was the only game in town. He grabbed a roll of thin aluminized mylar—normally used for insulation—and a canister of dark, soot-like carbon powder from an old air filter.

He turned to convection. “Fine,” he said, pulling up schematics of the backup loop. He could vent the reactor’s secondary helium coolant into a makeshift radiator—a long, coiled tube he could snake across the crater floor. But without a pump, the helium would move by natural convection only. He ran the Grashof and Prandtl numbers in his head. The buoyancy-driven flow would be too slow. The tube would melt before the heat ever reached the far end.