Gregory grunted. “If the Shuttle goes ahead. The studies are also going ahead for Mars landing missions. And there we are looking at more big dumb rockets. More V-2s.”

Dana grinned. “Those Germans, Dad?”

“It’s the crudity of their approach that galls me. Von Braun’s designs have always looked the same. For thirty years! Immense, overpowered machines! Leaping to the stars, by the most direct route possible!”

“The Germans got a man on the Moon,” Dana said gently.

“Of course. But it’s not elegant.”

Not elegant. And that’s not the Langley Way.

Gregory was saying, “Even the basic thinking about interplanetary travel has hardly advanced since Jules Verne.”

Dana guffawed. “Oh, come on, Dad; that’s hardly fair.” The lunar voyagers of Jules Verne’s nineteenth-century science fiction had been fired at the Moon out of a huge cannon, situated in Florida. “Even Verne could have worked out that the gun’s acceleration would have creamed his travelers against the walls of their projectile.”

Gregory waved his pipe. “Oh, of course. But that’s just a detail. Look — Verne launched his travelers with an impulse: a shock, a blow, imparted by his cannon. After that brief moment, the spacecraft followed an elongated orbit about the Earth, without any means of directing itself.

“And just so with Apollo. Our great rockets, the Saturns of von Braun, work for only minutes, in a flight lasting days. Effectively they apply an impulse to the craft. Even the Mars studies follow the same principles. Here — look here.”

Gregory walked to the blackboard and wiped it clean with the sleeve of his sweater. He rummaged in his cardigan pocket until he dug out a fluff-covered piece of chalk, and he drew two concentric circles on the board. “Here are the orbits of Earth and Mars. Every object in the Solar System follows an orbit around the sun: ellipses, flattened circles, of one eccentricity or another.

“How are we to travel from Earth, on this inner track, to Mars, on the outer? We do not have the technology to fire our rockets for extended periods. We can only apply impulses, hopping from one elliptical path to another, as if jumping between moving streetcars. And so we must patch together our trajectory, to Mars and back, from fragments of ellipse. We kick and we coast; kick and coast. Like so…”

Dana watched as his father sketched, and thought about Langley.