Shadow Watch

“Jeremy could have handled it, and the crew could’ve handled him,” she said. “The upside to the whole affair is that he and I got acquainted, and have stayed friends ever since.”

“I’m here for you, babe,” Jeremy said, pitching his voice down to an exaggerated macho tenor.

The tram stopped to discharge its three passengers on the east side of the VAB. Annie was the first off, and as she led the way toward the huge building’s guarded personnel entrance Nimec picked up on an abrupt change in her demeanor. There was a tension beneath the surface he could almost feel her struggling to control, a hurriedness to her step that hadn’t been evident when they’d left the reception area for the tram. Whatever was on her mind was something she’d chosen to keep to herself, and he could only admire her poise and composure in doing so.

The floor of the high bay area was as chaotic as she’d warned him it would be, but it was the organized chaos of people faced with a serious and complex task, and operating under intense pressure. He’d known it in combat, known it at police crime scenes, known it all too frequently since joining Roger Gordian’s operation; it was part of the game he’d played throughout his entire professional life. What struck him in this instance, however, was the absence of accompanying background noise, the purposeful silence of the men and women Annie had drawn together for her team, some in NASA coveralls, others in civilian clothes, dozens of them scurrying everywhere around and past him. Their silence, and the sheer amount of debris that had been collected here. As his eyes swept the enormous room, he knew it would have been impossible to fully comprehend the annihilating magnitude of the explosions that had wracked Orion on the launchpad without seeing these remains firsthand.

Nimec surveyed the feverish activity a while longer, then realized Annie and Jeremy had already gone on ahead, walking side by side, leaning their heads together in private discussion. He started after them, but on second thought decided to hang back. Though he’d met her a scant half hour ago, he already suspected Annie Caulfield had good reasons for whatever she did. And he had given his word not to crowd her.

He watched them walk up the broad transfer aisle stretching away before him and climb onto one of the movable work platforms, where four or five investigators were gathered over several large sections of the spacecraft. Annie spoke with them briefly, projecting an easy, gentle authority — paying close attention to their comments, patting one woman on the shoulder with the same sort of open, unself-conscious warmth she’d shown Jeremy on the tram. Nimec again found himself singularly impressed by her bearing.

When the group left the platform a few moments later, plainly at Annie’s request, she and Jeremy hunkered into what reminded Nimec of a palaeontologist’s crouch and began shuffling amid the wreckage, occasionally exchanging comments and pointing things out to each other.

After a bit Nimec figured it would be okay to join them.

Annie acknowledged him with a nod as he reached the foot of the platform, and then waved him over, continuing to inspect one of the shuttle fragments. A soldered clump of tubes and valves in a cracked, scorched housing, it was attached to a component that, though also burned and dented, nonetheless retained something of an identifiable bell shape. Nimec thought he could make an educated guess about what it was, but didn’t, not aloud anyway, wanting to give them some more breathing room.

Finally Annie glanced up at him from her crouch.

“You’re looking at what’s left of a main engine,” she said, confirming his hunch. “The shuttle has three of them below the vertical tail fin. It’s no secret that the recorded dialogue between Orion’s flight deck and ground control tells us a red warning light went on at T minus six seconds, and indicated Main Engine Number Three was overheating.”

He nodded. “This it?”

She paused before answering, then said quietly, “SSME Three was essentially vaporized in the initial blast. SSME Two, which was situated right beside it at the aft end, is being partially reassembled from what little of it we’ve been able to recover. You’re looking at SSME One. I’m not sure why, but it’s been left relatively intact. The engines are in a triangular configuration, and this would have been at the apex, so maybe its position above the other two allowed it to escape the worst brunt of the explosions in some way. That’ll be determined. What’s important to me right now is that we have it to study.”

“These mothers feed off a potent mixture of cryogenic liquid hydrogen and liquid oxygen,” Jeremy said. He was bent over the opposite side of the engine bell. “Annie’ ll correct me if I’m wrong, but I think the propellants in a shuttle engine generate 1.7 million newtons — that’s equivalent to, what, about 375 thousand pounds of thrust at sea level. Makes it the most efficient dynamo of a power plant ever built. On the other hand, the ignition of hot hydrogen gas can be savage unless it’s precisely regulated. Remember the Hindenberg.”

“Which means exactly what regarding Orion?” Nimec asked.

“Getting back to the shuttle-to-ground communications record, it’s apparent that a problem developed with the flow of liquid hydrogen fuel,” Annie said, her face solemn. “Again, this is information that’s been very widely circulated in the media, so I doubt I’m saying anything you don’t already know. One of the last things Jim… Colonel Rowland… said to the controller was that LH2 pressure was dropping. Then he broke off for a second.”

Nimec had listened attentively, but felt a little baffled. “If I’m following this at all, you’re implying a reduction in liquid hydrogen pressure may have caused the increase in engine temperature that in turn sparked the fire. But I’d think it’d be the other way around — less fuel, less burn.”

“Yeah, sure, unless the pressure drop is in these here strands of spaghetti,” Jeremy said. He gestured toward one of the clumps of mangled tubing behind the engine bell. “They channel the LH2 into the walls of the engine nozzle and combustion chamber before outletting them to the preburners—”

Nimec raised his palm to stop him.

“Whoa,” he said. “Back up a second. I’m still not clear on how less equals more in this instance.”

“That’s ’cause a very important word I used to describe the state of the liquid hydrogen must’ve slipped past you,” Jeremy said. “Namely cryogenic.”

Annie saw Nimec holding back his irritation at being patronized.

“As Jeremy said,” she broke in, “the SSMEs operate with a high level of efficiency. That’s in part because the propellants are used for multiple purposes. To remain in a liquid state hydrogen has to be kept super-cold… to give you an idea of how cold, bear in mind that it vaporizes at any temperature above minus 423 degrees Fahrenheit. As a solution to the problem of critical engine overheating, the designers of the SSMEs found a means to divert some of the liquid hydrogen fuel throughout the engine with a system of ducts before it finally makes its way to the preburners. There’s a pair in each of the main engines, and their function is to ignite the very hot hydrogen vapors that result from the combustion process before they can accumulate and ignite in the engine bell. If you ever watch a video of a liftoff in slow motion, you’d can see the preburners shooting the gas out below the bells as thousands of tiny fireballs.”

Nimec looked at her. “So you’re telling me that a significant dropoff in LH2 pressure would have caused the engine to overheat and the preburners to fail… leading to an explosion of the free hydrogen vapors in the engine bell.”

“That’s what Jim was telling us. Or trying to. He would have known where in the engine the liquid hydrogen pressure had critically decreased just by looking at a gauge on his instrument panel. But with everything happening so fast… the cabin filling with smoke…”

“He never finished saying what he wanted to.”

“Which was that the LH2 pressure was dropping in the preburner ducts.”

Their gazes met. Nimec saw the moist, overbright look in her eyes, realized she was fighting back tears, and found himself on the verge of reaching out with a comforting hand. Instead he stiffened, caught wholly off guard by the impulse.

Turning to Jeremy, he said, “When we were on the tram you mentioned the difference between knowing what happens given a certain set of conditions, and understanding why it happens.”

Jeremy visibly wavered.

“I was talking about snowflakes,” he said.

“Then talk to me now about explosions,” Nimec said. “What do you think made the LH2 pressure drop? And if it occurred in Engine Number Three, why are there fused cooling ducts in Number One? How could the identical problem simultaneously occur in at least two of the three