He hurried through the idea of gravity assist. He tried to emphasize the history and intellectual weight of the idea, showing that his own computations had built on the work of others. “The concept within NASA of using a Venus swing-by to reach Mars dates back to Hollister and Sohn, working independently, who published in 1963 and 1964. This was further elaborated by Sohn, and by Deerwester, who presented exhaustive results graphically in a format compatible with the direct flight curves in the NASA Planetary Flight Handbook…”

It was a little like a game of interplanetary pool, he said. A spacecraft would dive in so close to a planet that its path would be altered by that world’s gravitational field. In the swing-by — the bounce off the planet — the spacecraft would extract energy from the planet’s revolution around the sun, and so speed up; in exchange, the planet’s year would be minutely changed.

In practical terms, bouncing off a planet’s gravity well was like enjoying the benefit of an additional rocket stage at no extra cost, if your navigation was good enough.

“We have already studied the Mariner Mercury mission, which would have swung by Venus en route to Mercury. A direct journey would have been possible, using, for example, a Titan IIIC booster; but the gravity assist would have allowed the use of the cheaper Atlas-Centaur launch system…”

“Yeah,” a voice called from the audience, “but Mariner Mercury got canned. And there were no men on it anyhow!”

Laughter.

Dana pressed on, brushing the sweat from his eyes. There were two ways Venus could be used to get to Mars, he said. The spacecraft could swing by Venus outbound, and use Venus’s gravity to accelerate it toward Mars. Or Venus could be used to decelerate the craft, on its way back to Earth.

“First estimates show a mass in Earth orbit of two million pounds would be required for a mission duration of 640 days.” Same weight as nuclear; two-thirds the trip time of chemical. “Thus a mission profile close to optimal is delivered, without the need for ambitious new technologies, and hence significantly reduced development costs compared to other candidate modes…”

And it’s elegant. Don’t you see that? No brute force here: no huge nuclear V-2s. Just proven technology, and elegance, and style. A little thought, gentlemen.

“In conclusion, it has been shown that the Venus swing-by mode is generally applicable to all of the Mars flyby and stopover round-trip launch opportunities, with very favorable benefits.”

Dana stepped back from the podium, retreating from the glare of the light. He was numbed, a little giddy, unable to feel his hands or face.

Seger thanked him, then opened up for questions; with a glance at his watch he signaled that they should be brief.