Gershon didn’t fumble like that because he was nervous, York perceived wearily, but because he didn’t care enough to concentrate hard on what he was doing.

“This here is the ECLSS of your basic MEM configuration,” Gershon said. “Take a good look at it. Maybe your life is going to depend on knowing your way around this baby someday.”

The new slide was a block diagram of bewildering complexity, covered with spidery arrows and puzzling acronyms. The new picture showed no resemblance, as far as York could see, to anything she’d been shown before.

The snoozer ahead of York gulped and chewed on a loose piece of phlegm.

“Now,” said Gershon, tapping the diagram again, “here you have your basic ECLSS concept, which is likely to fly whatever choices we make about the rest of the MEM’s engineering. You have your standard two-bed molecular sieve here for CO2 scrubbing. And the H2O management is by means of this multifiltration unit here.” He pronounced the prefix mult-eye. “That supplements the output of your fuel cells. And your atmospheric gases are cryogenically stored, of course. As opposed to being stored under pressure.” Gershon blinked around the room. “Anybody figure out why that is? Because it’s a better weight-to-volume ratio. And we don’t operate any kind of O2 recovery system here. We take all our breathing air along with us, and just vent the waste. You want to tell me why? Because the MEM is a short-duration craft, and the weight of the recovery systems wouldn’t be justified…”

York realized that this trick of Gershon’s — of asking a question of his class and carelessly answering it before anyone got a chance to speak — was slowly driving her crazy.

Gershon told the class they should complete the copy of the diagram in their books, and he wandered out of the room in the direction of the coffee machine.

Although Gershon clearly knew his way around MEM designs, he was not a trained educator. He was a short, wiry, black man in his mid-thirties. Apparently he hailed from Iowa, but he’d been hanging around Houston long enough for a Texas drawl to color the way he pronounced his vowels, making the acronyms even tougher to cut through; ECLSS came out like “Aye she ale esh esh…” And after so many years here Ralph Gershon was just another rookie astronaut, still waiting for his first flight, plowing through another lousy assignment, lecturing to a new class of bright-eyed hopefuls.

For York, Gershon was a depressing role model.