York heard a muffled bang as pyrotechnic charges broke the metal belt holding the small retropack against the base of Challenger. Then there was a clatter against the wall, oddly like the footsteps of a huge bird: that must be the belt of the discarded pack, scraping along the hull.

With the retropack gone, Challenger was falling ballistically, like a projectile shot out of a gun. Its heat shield gave it the form of a blunt cone, the classic Command Module shape, though the MEM was nearly three times as big as an Apollo CM.

Gershon tipped up the spacecraft, so that the blunt prow of its base, where the titanium honeycomb heat shield was thickest, led the way into the gathering air. When he fired the attitude thrusters York saw brief bursts of gray mist, beyond the small window above her.

Then the mist got more persistent, in short bursts of translucent paleness, that lingered even after Gershon had stopped firing.

Soon the mist started to turn pink. There was a thin whistle beyond the hull.

The glow was the air of Mars, its atoms smashed to fragments by impact with Challenger’s heat shield.

Gershon whooped. “We’re getting close! Old papa Mars has us!”

“Goddamn,” Stone said, his voice tight.

The first feather touches of deceleration settled over York: a gentle pressure inside her stomach, a faint heaviness about her legs.

A light went on at Gershon’s station.

“Gotcha!” he shouted. “That’s point zero five G. This is going to be a real ride. Hang on.”

Point zero five G: the traditional threshold of atmospheric drag. And here they were, reaching point zero five G in the air of Mars.

The deceleration piled up on her in sudden, brutal steps. It’s bumpier than the sims. This air is supposed to be thin, damn it. There must be a more complex structure of layers in the atmosphere than had been realized, a sharper differentiation.

The pain at her chest was already exquisite.

She kept her eyes wide-open, trying to remember every detail. Every ounce of pain will tell someone, some atmospheric scientist, more about Mars. After all, she might be one of just three people in history to endure this.

Somehow, though, at this moment it wasn’t worth it.

She heard the crisp rattle of the attitude control thrusters’ solenoids.

Gershon watched his guidance display. “Right on track. One forty-seven degrees…”

Challenger had to hit a precise reentry corridor. The allowable guidance error either way was only half a degree: less than fifty miles wide.

“Coming up on one G… now.”

Just one G? Already York felt as if her suit was made of lead tubes, as if some fat man was sitting on her chest. Can this really be Earth-normal gravity? After a year in microgravity, the burden seemed intolerable, like carrying a huge pack around on your back, for your whole life.

“One point five,” Stone said.