Dana grinned. “Still not elegant enough for you, Dad? But where’s the room for elegance in all this? It seems we’re kind of constrained by the laws of celestial mechanics. It’s either Hohmann, or brute force.”

“Exactly. So the elegant thing to do is wait: wait until we’ve developed a smart engine, like an ion drive, which can really cut down the transit times. But that won’t come in my lifetime, and maybe not yours.”

“Hmm.” Dana took the chalk from his father and drew more concentric circles. “Of course, you didn’t show the full picture here. There are other planets in the system: Venus inside Earth, Jupiter beyond Mars. And the others.”

Gregory scowled. “What difference does that make?”

“I don’t know.” Dana dropped the fragment of chalk back into his father’s pocket. “You’re the specialist.”

“No, no, this is not my field.”

“Maybe there is some way to use the other planets, to get to Mars. There are NASA studies going on of a Grand Tour: using the gravity field of Jupiter and the other giant planets to accelerate a probe out to Neptune…”

“So what are you suggesting? That we fly to Mars via Jupiter? That’s ridiculous. Jupiter is three times as far from the sun as Mars is.”

This tone — hectoring, impatient — was all too familiar to Dana. He held his hands up, irritated. “I’m not suggesting anything, Dad. I’m just chewing the fat. The hell with it.”

But Gregory continued to stare at the board, his eyes invisible behind the layer of chalk dust on his glasses. Some remark of Dana’s had sent him off, like a Jules Verne impulse, on some new speculative trajectory of his own; Jim Dana might as well not have been there.

The hell with it, he thought. I have my own life now, my own concerns. I don’t have time for this anymore.

Maybe I never did.

Dana withdrew from the workshop, brushing the dust off his jacket, leaving his father to his thoughts.

He spent the rest of the afternoon with his mother. They sat on the swing seat back of the house, drinking homemade lemonade and talking in the warmth of the sun. In the distance, seagulls cried.

Gregory Dana carefully sketched interplanetary trajectories.

…At age fifteen, in the year 1944, Gregory Dana was no rocket engineer. In fact he was no more than garbage, just one of the thirty thousand French, Russians, Czechs, and Poles who toiled inside a carved-out mountain in Thuringia.

Everything was slow — even dressing was slow — and Dana was already hungry by the start of his work at 5 A.M. And yet he would receive nothing until his soup, at two in the afternoon.