We were silent for a moment. We both knew a miss would be fatal. If the capsule didn't reach high enough for Farside to catch it, it would oscillate back and forth over a matter of days, slowing gradually and finally coming to a rest at the core of the Moon. Rachel would run out of oxygen long before then.

"Will she make it?" I asked.

André didn't answer. He loaded an analysis tool and started typing furiously. I couldn't wait. I grabbed a pen and a safety manual and started writing equations on the back. The math was complex, but it was also the basis for the project I'd been working on for eight years. The catching mechanism was designed to be extended down into the tunnel to account for slight variations in velocity; the question was, could it extend far enough to catch Rachel?

We reached the answer at almost the same moment and looked at each other without speaking, both praying that we were wrong.

Finally, I said, "She'll fall 10 m short."

André nodded.

The comm beeped. I punched it and growled, "What is it?"

"Dad?"

"Rachel! Are you safe? Everything OK?"

"I'm fine, Dad. My air is good, my temp is good. Farside's going to catch me, right?"

I didn't hesitate. If there was anything I knew as an astronaut, it was that people do better when they have all the information.

"Negative. Repeat, negative. You hit some friction at the core. You won't reach the magnets." I coughed, then said, "We're going to catch you on this side."

She knew as well as I did that the loose dirt would cut her velocity even more on the return trip. Her response was quiet and simple. "How?"
I shook my head. "I don't know."

Rachel's capsule fell short exactly as our calculations predicted and started the long fall back toward the core.

"If there were only some way to speed her up..." André tapped a pencil on the screen in nervous frustration.

"Forget about it. No rockets, no means of propulsion, nothing to push out the back."

Propulsion meant energy, and there was no more energy in the system.

"Could we fire the laser at the capsule, cut a hole in the top?"

"What, and have her jump out?"

André shrugged. "If she jumped just at the top of its rise, in the moment the capsule was completely still, she could prop herself up in the tunnel with her legs and arms until we could pull her out."

"Hold herself up in a sheer concrete tunnel over a several-thousand kilometre drop?"

"If it's her only chance, it's better than nothing."

I held up my hands. "I'm sorry. But it won't work. The tunnel is gravitationally straight, but it's not actually straight, remember? It has to account for mascons and mountains. You can't reach her with a laser until she's too close to do any good."

We argued for several more minutes, but finally settled on the only possibility. We had no more time to talk if we wanted time to prepare. The only remaining disagreement was who would go down The Hole.

"There's no question, André. You have to work the numbers. They need to be perfect – correct to the centimetre. This isn't something you want me doing on the back of an envelope. If it isn't right ... well, we'll only get one chance at this."

André nodded. "I'll get it right."

"You do that."