“Yeah, that’s standard procedure,” Muldoon put in. “Without coolant, the core is going to overheat.”

“We had a split second to make the decision,” Udet said. “That is all. If we had allowed emergency shutdown immediately, we might have lost the engine altogether, and the mission would have been scrubbed. And perhaps for nothing, if the flow problems had rectified themselves. We were trying to keep options open. The report describes all this.”

“All right, Hans. Go on.”

“We adjusted the moderators to reduce the temperature in the core, short of shutting it down. But we could not reach the target temperature—”

Muldoon said, “And there you have your first basic design flaw, Fred.”

Both Udet and Seger leaned forward to protest, but Michaels waved them silent.

“We only had one control system — the reactor moderator — and so only one shutdown option. When that failed, we had no way to stop the runaway temperature climb.”

Michaels nodded. “Hans?”

Udet spread his hands. “We must balance reliability against weight, Fred. This has been the dilemma of all spaceflight: to carry an additional redundant system, or to add value elsewhere? In our opinion, in this case, the moderator system was sufficiently reliable to justify flying without the weight penalty of a backup.”

“Bert? You want to comment?”

Seger, his eyes brilliant, shrugged his narrow shoulders. “We made the best call we could; we did all the tests. We got it wrong. Next time we fly a NERVA, we’ll fix it.”

These things happen. Not an answer to satisfy the Presidential Commission, Michaels thought sourly.

“Go on, Hans.”

“By now,” Udet said, “the crew was aware that the thrust had died, after that first shove. We were only a few seconds after the first glitch in the flow. Now the hydrogen flow increased, markedly,” Udet continued. “It was like a spurt, from the faulty piping. The hydrogen passed its nominal flow rate and effectively flooded the core. We withdrew the moderator further—”

“And this is another point at which the standard procedure said shutdown,” Muldoon said harshly. “The moderators’ control margin was too low now; we didn’t have full control of the core. But again, we overrode the automatics.”

“We tried to save the mission,” Udet said.

“All right. Let’s stick to the facts for now; we can justify ourselves later. What next?”

“Now the flow of coolant into the core stopped altogether,” Udet said. “Perhaps at this point the piping failed completely.”

“This is the key moment, Fred,” Muldoon said. “You have a reactor that’s already unstable. The hydrogen flood has made the core isothermal — that is, at the same temperature throughout — so any changes happen all over the core, simultaneously. And the coolant flow has stopped; the core’s main heat sink, the flow of hydrogen through the jackets, has gone.”

“So it starts to heat up.”

“So it starts to heat up. Uniformly. And a lot faster than before.”