Next up was a project manager from General Dynamics. He got to his feet with a broad grin gleaming from out of a California tan. “I’ve got to tell you,” he told the audience deadpan, “that I can beat you NERVA folks hands-down. With two million pounds in Earth orbit I can get to Mars and back in just 250 days — not much more than half your time — and taking no less than twenty guys. Gentlemen, I give you Project Putt-Putt.”

The idea was to throw one-kiloton nuclear bombs out of the back of the spacecraft — thirty devices every second — and set them off, a thousand feet behind the ship. The shocks would be absorbed through water-cooled springs, and the ship would be driven forward. “Like setting off firecrackers behind a tin can. Am I right?”

The concept seemed ridiculous, but General Dynamics had done some preliminary studies, called “Project Orion,” in the early 1960s, and the presenter was able to show photographs of a small flight-test model which had used high explosives to hurl itself a few hundred feet into the air.

The technical problems were all around the high temperature flux on the rocket’s back end structure, which would have to radiate away excess heat between explosions. And of course the system had one major drawback, the General Dynamics man said, and that was the radioactive exhaust. But that hadn’t seemed such an obstacle back in 1960, when the first Orion studies had been initiated. Then, it was thought that the unscrupulous Soviets might use this quick-and-dirty method to short-cut to space, so we had to look at it, too.

The General Dynamics man joshed and wisecracked his way through his talk. When he sat down he got the biggest hand of the day.

Dana felt himself shrink into his seat. How the hell do I follow that?

When he got to the podium Dana shuffled with his notes and foils, trying to avoid looking out over the sea of sleek suits before him. There was a spotlight on him; it seemed to impale him. It was already four-thirty, and after the General Dynamics pitch the delegates had lost concentration; they were still laughing, talking.

Dana began to read from his notes. “Manned Mars stopover missions of duration twelve to twenty-four months are characterized by Earth return velocities of up to seventy thousand feet per second, over the cycle of mission opportunities. A promising mode for reducing Earth entry velocities to forty to fifty thousand feet per second, without increasing spacecraft gross weight, is the swing-by through the gravitational field of Venus. Studies indicate that this technique can be applied to all Mars mission opportunities, and in one-third of them, the propulsion requirements actually can be reduced below minimum direct-mode requirements…”

There was a ripple of reaction in the audience, a restless shifting. Dana plowed on. He felt sweat start over his brow, around his collar.