Sims were spring-loaded to fail. That was the point, really: to familiarize crew and controllers with all the myriad ways the mission could go wrong, and train them to cope. However, York had the feeling that Ralph Gershon was spring-loaded the other way. It is going to take a lot to keep him from landing this bucket of bolts.

And that, as far as York was concerned, was good.

“Fifteen seconds,” Stone said. “Ten seconds to DOI. Here we go, guys. Eight. Six, five, four.”

Gershon’s gloved hand closed over the firing button.

“Two, one.”

The rockets fired in sequence. It was a muffled, rattly noise.

And then came the jolt, deep in her back.

“Retro light on.” Gershon flashed a grin. “Beautiful! Pure gold!”

It felt as if Challenger had been knocked backwards. Solid rockets, she’d been told, always burned a lot more crisply than liquid.

The burn went on, with Stone counting up the time. The rockets’ thrust of forty thousand pounds force was too small to shove seriously at the mass of the MEM, and so there was no rattle, no vibration, no real sense of deceleration. Just a steady push at her back, a smooth hiss as the retropack burned.

The push died sharply. Right on cue, the retropack had cut out.

Nothing felt different. Challenger was still in orbit around Mars, for the time being, and York was still weightless, floating within the restraints which held her to her couch.

But the MEM was following a path that would bring it arcing down until it sliced into the Martian atmosphere, at maybe thirty miles above the surface. And the drag of the atmosphere would not allow the craft to climb out again.

Challenger was committed to Mars.

Suddenly she got an unwelcome sense of perspective, a feeling of how small and fragile the little capsule was. It was different from landing on Earth. On Earth you were descending toward an inhabited planet, toward oceans full of ships waiting to pick you up.

Out here there were only the three of them, jammed up against each other in their little pod, descending toward a dead world. So far from Earth they couldn’t even see it. Out here, they weren’t closing off their journey, coming home; out there, they were pushing out still farther, into extremes of technological capability and risk, so far from Earth that Mission Control couldn’t even speak to them in real time. It was like climbing the ladder one more rung.

But what York felt was not fear, but mostly relief. Another abort threshold crossed. The farther the mission went, the fewer things were left to go wrong.

“Coming up on jettison retro,” Gershon said.

Stone counted him down. “Three, two, one.”