Vance walked across to the central seat, studying the console. The throttle quadrant and sidestick he understood, but most of the other controls were new to him. Maybe it didn't matter.
"Does Petra understand English?"
"Of course," Androv nodded. "Russian, Japanese, and English. Interchangeable. She's programmed such that if you command her in Russian, she replies in Russian. If you use English, that's what you get back."
"So far, so good." He looked at the large screen at the end of cabin, the one that displayed Petra's mindstate. She was dutifully announcing that she'd just taken the vehicle to three thousand meters. She also was reporting the IR interrogation of a wing of MIG 31s flying at twenty thousand feet, with a closure rate of three hundred knots. When Daedalus made her move, would she be able to outdistance their air-to-air missiles?
We're about to find out, he thought, in—he glanced at the screens—three and a half minutes. Eva was zipping up her pressure suit now, readying to strap herself back into her seat. The helmet made her look like an ungainly astronaut.
"Like I said, the scramjets become operable at Mach 4.8," Androv went on. "At forty thousand feet, that's about three thousand miles per hour. I've never taken her past Mach 4.5." He was grasping the side of the console to brace himself. "You probably know that scramjets require a modification in engine geometry. In the turboramjet mode, these engines have a fan that acts as a compressor, just like a conventional jet. However, when we switch them over to scramjet geometry, the turbines are shut down and their blades set to a neutral pitch. Next the aft section of each engine is constricted to form a combustion chamber—the shock wave inside becomes the 'compressor.' " He paused. "The unknown part comes when the fans are cut out and the engine geometry is modified. I've unstarted the fans and reconfigured, but I've never fed in the hydrogen. We simply don't know what will happen. Those damned turbines could just explode."
"So we take the risk."
"There's more," he continued. "The frictional heat at hypersonic speeds. Our liquid hydrogen is supposed to act as a heat sink, to dissipate thermal buildup on the leading edges, but who the hell knows if it'll work. We're now flying at about fifteen hundred miles per hour. When you give Petra the go-ahead, we could accelerate to ten, even fifteen thousand miles per hour. God help us, we may just melt."
"If you were willing to give it a shot, then I am." Vance looked up at the screens. "We're now at ten thousand feet. I kick over to scramjets at forty thousand?"
"The computer simulations all said that if we go hypersonic below sixty thousand feet, we could seriously overheat. But maybe if we climb out fast enough . . ."