“Right. The balance is lost.” Muldoon looked over the report once more. “These babies propagate. A free radical will return to normal by stealing its neighbor’s electron. But that makes that neighbor into a free radical in turn. Your body has a scavenger system to fight these things, but it can get overwhelmed or inactivated. And then the damage you suffer depends on what gets hit. You can get radiation-induced cancers if a DNA base is damaged, or your system loses control of its functions if protein is damaged, or you can get internal bleeding if membrane lipids are broken.”

Bleeker frowned. “Membrane lipids, Joe?”

Muldoon tried to put together an answer in plain English: how free radicals contributed to aging, and cancers, and degenerative diseases of the heart, liver, and lungs; how the loss of free-radical balance contributed to a lot of other microgravity problems like disturbing the inner ear’s balance mechanism, and bone degeneration…

“Look, Adam, you ever left a slab of butter out in the sun?”

Bleeker thought about it. “Gets rancid.”

“Well, there you are. That’s free radical damage.”

Bleeker, his eyes locked on Muldoon’s, started pulling at his cuff, in a precise, apparently unconscious gesture.

Bleeker really did seem to have a kind of inner calm, an even temper. It had evidently gotten him through all that A-war shit he’d trained for, Muldoon supposed. Maybe the psychs were right, that Bleeker had a lack of imagination.

But Muldoon could see the tension building in him, under the surface. How was he going to react to this, the worst news of his life?

“Look, Adam. You have to understand. You’re not ill. It’s just that because of this kind of study, they’ve tightened the limits. On everybody. And you, with all your exposure to space, have finished up outside the limits. If the free-radical study had come in a couple of months earlier you probably would have been bumped off D-prime, too. Look — you might have suffered some of this free-radical damage. Or not. Or something else—”

“I’ve proved myself in space, Joe, and on the ground, time and again. Look how I pulled off the D-prime flight. I deserve this goddamn trip.”

“I know that, but—”

“And I know about surgeons’ reports. They talk about risks. Likelihoods and percentiles. Not certainties. And besides, it isn’t logical. The Ares crew is going to run up a lot more time in space than I’ve accumulated anyhow.”

“But starting from a lower base, Adam. Even Phil Stone.”

“Joe, I don’t care about the risks. I want to go anyhow.”

“If it costs your life?”

“Even so.”

Bleeker lifted up his head, and there were those wide, church-window eyes looking right into Muldoon, open, honest, committed.