“Umm.” Frank pulled at his lip. “Your mission, should you choose to accept it…” He pulled over another napkin, and sketched Earth and Moon, this time as two spheres. He drew tight circular orbits around each of Earth and Moon, then a figure-of eight around the two worlds.

“Let’s be specific about what we have to achieve here. If we are restricted to the current fleet of medium-lift vehicles, we have to consider Earth orbit rendezvous. Several launches, by the Shuttle and other vehicles, carrying up the components of the mission, to be assembled there. Probably using Station as a refuelling shack.

“First of all we need propellant for the TLI burn.” He drew a little arrow, at the Earth end of the figure-8. “Trans-lunar injection. We coast for three days to the Moon. We need our habitat vehicle to keep us alive. Then LOI: lunar orbit insertion, another burn, which we have to carry fuel for, to place us in orbit around the Moon. Next, into the lander. A deorbit burn, descent, soft-land standing on your rockets. More fuel, of course. Ascent back to orbit, maybe using the same engines — maybe not, like Apollo. Rendezvous in lunar orbit. Then the trans-Earth injection, coast back to Earth, probably aerobrake to orbit and have Shuttle come pick you up.”

“Pretty much like Apollo,” Jays said.

“Well, the rules of celestial mechanics haven’t changed. Almost certainly this architecture is going to provide us with the minimum-weight configuration. You could consider direct-ascent, for instance, where you take your whole ship, transfer habitat and all, down to the surface… But we ran some studies a few years ago along these lines, about how light, how cheap you could get. It wasn’t encouraging.”

“Stick to what you have,” Geena said.

“Let’s start with the lander. Everything else is going to scale to that. Now, the old Apollo Lunar Module was around sixteen tons, full up weight. But that included a surface shelter for six man-days on the Moon, effectively. And there were a lot of structural costs in the mass estimates, because of the split between ascent and descent stages, and the nature of the design. We did some studies that showed you could cut that to maybe a quarter.”

Jays snorted. “Bull hockey. Believe me, that old LM was just a bubble of aluminum. Those Grumman guys shaved it thin.”

Frank grinned. “Old man, that bird will look like a Chevy compared to what I’ll show you now.” He quickly sketched an Apollo LM, the familiar spidery descent stage, the bulbous ascent stage. “The whole thing stood maybe twenty-three feet tall. Now look at this.” Alongside he sketched something that looked like a scale model of the Apollo descent stage. There,” he said. “Six feet tall. Nothing but fuel tanks, legs and a rocket engine. The structural integrity is actually expressed through the tanks themselves.”

Jays looked closely. “No ascent stage?”