“Och,” he said. “The shields are triply protected. They won’t fail.”

That would have reassured me, but then he had rubbed his high, balding forehead and added, “And if they do, it won’t make any difference if you are ten meters away, or five hundred. That kernel would radiate at about two gigawatts, most of it high-energy gammas.”

The trouble was, he always had the facts right. When I first met McAndrew, many years ago, we were taking the first shipment of kernels out to Titan. He had showed up with them, and I assumed that he was just another engineer — a good one, maybe, but I expected that. Five minutes of conversation with him told me that he had probably forgotten more about Kerr-Newman black holes — kernels — than I was ever likely to learn. I have degrees in Electrical Engineering and Gravitational Engineering, in my job I have to, but I’m really no gravity specialist. I felt like an idiot after our first talk. I made a few inquiries, and found that McAndrew was a full professor at the Penrose Institute, and probably the System’s leading expert on space-time structure.

When we got to know each other better, I asked him why he would give up his job for four months of the year, to ride herd on a bunch of kernels being shipped around the Solar System. It was a milk-run, with lots of time and very little to do. Most people would be bored silly.

“I need it,” he said simply. “It’s very nice to work with colleagues, but in my line of business the real stuff is mostly worked out alone. And I can do experiments here that wouldn’t be allowed back home.”

After that, I accepted his way of working, and took vicarious pride in the stream of papers that appeared from McAndrew at the end of each Titan run. He was no trouble on the trips. He spent most of his time in the Sections carrying the kernels, only appearing in the Control Stage for his meals — and frequently missing them. He was a tinkerer as well as a theorist. Isaac Newton was his idol. His work had paid off in higher shielding efficiencies, better energy extraction methods, and more sensitive manipulation of the charged kernels. Each trip, we had something new.