Gershon peered out. He saw a fat number “three” stenciled on the tarmac, maybe a quarter mile away; it would be kind of fitting to come down slap in the middle of that, in this MLTV Number Three.

He used his attitude controller to tip up the MLTV until the numbered marking on his windshield overlying the target matched the number displayed by the computer on the CRT. “Thirty-eight,” he called out to Curval.

The MLTV started to float toward the target. Now, the PGNS program was computing a trajectory to take him to the “three” — or rather, to a position just above it.

“I don’t know the math behind it,” Curval said, “but you’ve got to know the basics, Ralph, to follow the logic of this thing, here.”

“I know it.”

“The PGNS works by the same system, basically, as the old Lunar Module. And there’s enough equipment on the MLTV, a computer and a radar, to let you do a complete Powered Descent. What you have is your computer taking your current position and velocity, and your target vector — which will be hovering, just above the ground — and it works out a nice smooth curve between the two for you to follow. Every couple of seconds, it recomputes, and figures out another curve. And the numbers it flashes up on the CRT tell you where to look on your reticles, and you should see your computed landing site right there, behind the mark.”

“I got it.” He swept across the tarmac, smooth, easy.

“If you want to change the landing site, you just use your attitude control to swivel and point your window, and the PGNS starts recomputing. You can set to ATTITUDE HOLD and just glide for a while, if you like. And you can change your down velocity by—”

“I know it, Ted. I—”

York came on the line. “Ralph. It’s Natalie. I think you ought to pull out.”

“Huh? Why?”

“You’re coming in too fast. Too low.”

He checked over the crude instrument panel. Everything looked fine to him. It was true he was coming in low and fast, but that was intentional; he knew all of Curval’s gassing hadn’t left him a lot of time, and he didn’t want to run out of fuel. “What’s your problem, York?”

“I think you’re going to overload the PGNS.”

“Come on. Everything up here is sweet as a nut.”

“It’s not as simple as that, Ralph.” She started gassing about best-fitting polynomials and higher-order curves, and a lot of other crap that went right over Gershon’s head.

He just tuned her out.

He watched the tarmac roll away under him. He swept along, the PGNS working smoothly; he barely needed to touch his controls. He felt a surge of success, of achievement. Here’s something else I can do, Ma. Another step on the long fucking ladder I’m climbing to Mars.