The computers worked constantly to update the numbers, and making sense of them wasn’t easy. He had to check the data-source slots at the top right-hand corner of the screen, to make sure that the sources of his numbers were all still updating him properly, and he had to be sure that he wasn’t diagnosing some problem incorrectly because of a mismatch in numbers of different vintages, fifteen or thirty seconds old.

But he discounted all that. He understood exactly what the silent parade of numbers was telling him. And it wasn’t good. The NERVA core was still overheating.

He tried to increase the flow of hydrogen through the core. That would take away some of the excess heat.

He got no response. In fact, one readout told him that the volume throughput of the hydrogen was actually falling.

Maybe there was a problem with a hydrogen feed line. Or maybe a pump had failed. Or maybe it was his old enemy, cavitation, somewhere in the propellant flow cylinders.

The core’s temperature continued to rise. More screaming in his ear.

Damn, damn. He’d have to abort the burn. And that was probably the end of the mission; he doubted they’d be allowed to go ahead with another engine restart after that.

He sent a command to the engine’s moderator control. He would slow the reaction in the NERVA core, reduce the temperature that way.

He got no response.

If the temperature had gotten high enough, the fuel elements could have distorted, even melted, and it would be impossible to insert the control elements into the core. Was that happening already?

If it was true, there wasn’t anything he could do to retrieve the situation. As he watched his numbers evolve, Conlig felt the first touches of panic.

Priest could clearly see the cones of the volcanoes of Hawaii, upthrusting, broken blisters. Earth receded visibly, as if he were rising in an elevator. The ride was exhilarating.

He felt a surge of elation. The damn nuke works.

It unraveled with astonishing speed.

Conlig watched power surge through the overheating core. After that, the resistance to hydrogen flow through the core sharply increased. Bubbles built up everywhere. The nuclear fuel assemblies were starting to break up. Pressure rose abruptly in the propellant channels, which were also beginning to disintegrate.

The whole structure of the core was collapsing.

The pressure in the reactor began to rise, at more than fifteen atmospheres a second. And, because of the massive temperatures, chemical and exothermic reactions were starting in the core.

And the increased pressure inside the reactor backed up to the pumps, and the pumps’ feedback valves burst. With the pumps disabled, the flow of hydrogen through the core stopped altogether.

The reactor’s main relief valves triggered, venting hydrogen to space. That offered some respite. But the discharge was brief; unable to cope with the enormous pressures and flow rate, the valves themselves were soon destroyed.