Muldoon opened the folder on his desk. It was the preliminary surgeon’s report from Bleeker’s D-prime mission postflight checkup. He started leafing through it, through the metabolism graphs and radiation dosimetry charts and countersigned forms and all the rest, wondering where to begin. “Hell, Adam. You know how it is with surgeons. You only walk out of their office two ways: fine, or—”

“Or grounded. And I’m grounded. Is that what you’re going to tell me, Joe?”

Impatient, Muldoon banged the folder closed with the palm of his hand. “Adam, you’ve spent a hell of a lot of man-hours in space, in Skylab, Moonlab, and now D-prime—”

Bleeker ducked his head.

“In fact, that’s one of your main qualifications to be on Ares. Right? We know you can cope with long-duration missions, because you’ve done it already. And now you’ve got experience with the MEM, the new technology… But you know that space exposure gets to you in the end.”

“So what’s the problem? Muscle wastage?” For the first time Bleeker looked vaguely alarmed. “Is it my heart?”

“No,” said Muldoon quickly. “As far as I can tell from this crap, your heart is fine. Adam, you’ve always been outstanding in adhering to your exercise regimes. Your muscle decline has been small, every trip, and you’ve recovered quickly.”

“What then? Calcium loss?”

“Not that. Adam — it’s radiation exposure.”

“I’m within the limits,” Bleeker said quickly.

Muldoon tried to suppress a sigh. “Yes, but they changed the rules on you, pal. To be fair to the surgeons, they keep on learning; they still don’t know much about the effects of long-term low-level radiation exposure, and they keep on coming up with new ways for you to get hurt… Listen: what do you know about free radicals?”

Bleeker frowned.

“Free radicals are bits of molecules. Highly energetic. Like ions — with charges knocked out of their atoms — only with more horsepower. They’re highly oxidizing, which means they have a taste for hydrogen. They’ll strip hydrogen atoms out of nearby molecules, even. And that can cause havoc if it’s happening inside your cells.

“Now, we’ve all got free radicals in our bodies. We need them for the operation of the metabolism. But there’s a balance. Your body produces them, and absorbs them, and keeps everything together. But if you’re exposed to high-energy radiation, or light, or extremes of temperatures—”

“You get more free radicals.”