He laughed. “Actually, that’s true. In low Earth orbit you’re protected, to some degree, by the magnetosphere. Outside, you’re exposed. But NASA does have an exemption, for ‘exceptional exploration missions.’ ”

“So they’ve covered their asses.”

“Yeah. Just like the Air Force. CYA.” He looked at her, his face unreadable. “You know, there is a lot of hazard out there, out of the shelter of the magnetosphere. You’ve got your solar particle events — solar flares, where you hide in your storm shelter — but there’s also the constant background radiation, cosmic rays from the galactic background. And women are—”

“Fifty percent more susceptible to radiation risk than men. I know, Adam,” she said.

His face was distant, inward looking. “You know, you can feel the difference up there. You’ll have to experience it, Natalie; I can’t describe it. You can feel the blood flowing through your heart valves, into your vessels. You come home with ‘chicken legs,’ as we call them. All that goes away. But then you’re hit by a kind of rapid aging… You know, Natalie, I’m not the only one.”

“The only what?”

“The only astronaut who’s come down like this. Nobody else on the active list has been grounded specifically because of radiation exposure, as far as I know. But some of the older guys, who flew in the 1960s, are showing up now with osteoporosis. Cancer. They’re turning up in their fifties and sixties, dying from risks you don’t find in the normal population.”

She felt cold; she put her fork down. “But those guys only had spaceflight records of two, three weeks—”

“Yeah. But we’ve spent four billion years adapting to life on Earth. For a while we thought spaceflight was easy. I guess we really do put our lives on the line, right? But then, some people seem to adapt well. They come home with trivial amounts of muscle atrophy, for instance. Maybe you’ll be lucky, Natalie. Maybe you’ll be an immune…”

“Well, if we were in a rational world,” York said, “we wouldn’t have a mission profile like Ares anyhow. The Ares plan is really a relic of the sixties.”

“Yeah. When the emphasis was just on getting there, not on what you do when you get there. If we were smart, we wouldn’t plan for a thirty-day stopover; we’d look to put you up there for a year. On the Martian surface you’d be relatively protected. On your brief little trip you’ll soak up almost as many REMs as on a Hohmann mission twice the duration, which would earn you five hundred days on Mars. On this one mission, you’ll come close to your legal lifetime dosage.”

“According to OSHA guidelines, right?”

“Yeah. Anyhow,” he went on, “a long stopover on Mars would probably be better for you anyway, to give you time to recover from the effects of the long zero-G transit…

“Ah, hell.” He pecked at his food. “You know, you could say we’re not ready to do this, yet. We’ve been studying Mars mission options for thirty years. Right back to von Braun. And the basic problems — the energy needed to get out of Earth’s gravity well, to cross interplanetary space — none of that has changed. And we haven’t come up with any fundamentally smarter solutions than von Braun’s, either. We’re still firing off big hydrogen-oxygen rockets, because we don’t see what else we can do.”

She felt pleased, to hear someone like Bleeker talk like this. Maybe the culture was changing, slowly. But he might have been discussing baseball scores for all the inflection in his voice.

“I can never read you, Adam,” she said frankly. “You know, I’ve often thought the same thing. That we’re not ready to go yet…”

He nodded, smiling faintly. “I figured.”

“But it won’t stop me going, anyhow.”

“No. And it wouldn’t stop me, if they’d let me.”

“You’re not trying to talk me out of it?” She tried to inject some humor into her voice, but wasn’t sure how successful she was.

“I would if I thought I could,” he said seriously. “Not that it would do me any good.” He shook his head. “You know what was the hardest thing?” he asked suddenly.

“What?”

“When I had to explain to my boy — Billy — that I’m not going to Mars. Damn,” he said, and he gazed out of the window at the muggy Houston sunlight.

She couldn’t think of anything to say.

He ate a little more of his lasagna. Mission Elapsed Time [Day/Hr:Min:Sec] Plus 371/01:32:30

Gershon gave Challenger’s attitude control rockets a final blip, a squirt to make sure they were functional.

Solenoids thumped.

“Everything is copacetic, guys.”

Stone’s face, behind his scuffed faceplate, was set, almost grim. “Good. Then let’s get the hell on with it,” he said.

Gershon grinned.

With a clatter of explosive bolts, Challenger kicked free of the rest of Ares. Then came a brief burn of the retropack, the small solid rocket cluster strapped to the base of the MEM.

The burn knocked Challenger into a new, low orbit around Mars.

York, strapped into her acceleration couch, tried to relax. Challenger would stay in its new orbit for a couple of revolutions, while the two pilots and the controllers back in Mission Control checked out its systems.

The MEM’s ascent-stage cabin, buried within the conical upper heat shield, was more or less a vertical cylinder, rising up above her. The three acceleration couches were crammed into its base, side by side. She could see, at an angle, the navigation and guidance panels with their big false-horizon displays, and the alignment optical telescope thrusting down from the ceiling.

The cabin’s main windows were big triangles, angled to face downward, so the pilots, when they stood up, would be able to see their landing site. And there was a small rectangular sighting window directly above her, with a matching panel cut in the upper heat shield. York stared up at that little window; trapped between the two pilots, she felt like a prisoner, staring up at a small window in the roof of her cell.

Where the interior of the Apollo Command Module had a warm feel to it — all browns and grays and greens — this cabin was mostly unpainted aluminum, thin and delicate and somehow unfinished. She could see lines of rivets, stitching the thing together. To York, the raw look spoke of a hurried development, a less mature technology than Apollo.

Through the window York watched Ares recede from the MEM.

It was the first time she’d seen the craft from the outside since the rendezvous in Earth orbit. The fat, faithful MS-II injection engine was still evidently the stack’s center of gravity — though the two External Tanks were long discarded — and ahead of it was fixed the slim MS-IVB stage which would brake them back into Earth orbit. The whole of Endeavor, their cylindrical Mission Module with its solar array wings, had been separated from the MS-IVB, turned around and redocked nose first; the idea was to free up the MEM from its shroud at the Mission Module’s base. Meanwhile Discovery, their Apollo, was docked to a lateral port, so it dangled sideways from the Mission Module, like a berry from the line of fuel-tank cylinders.

When Challenger returned to Martian orbit, the MEM would be discarded, and the remaining modules — booster stages, Mission Module, and Apollo — would be reassembled, once more, in a straight line, for the burn home.

The cluster was a collection of cylinders and boxes and panels, crudely assembled — and clumsily repositioned since their entry into Martian orbit. To York, all the orbital construction work — sliding modules through space like kids’ construction blocks — was unnerving. When they separated the Mission Module from the boosters, they were cutting themselves loose from their only ride home, for God’s sake! But she understood that there were backup strategies at every stage, ways they could reassemble some kind of configuration that could tolerate a ride home, even if they lost the landing.