She spoke to him of simple family matters. Vitalik asked me to say hello, she said. Vitalik was Lusia’s son, Arkady’s nephew. He is at summer camp. He is getting happier. He swims in the sea, he rehearses plays, he is doing arts and crafts. It was different in our day.

“Yes.” At the Soviet pioneer camps when Arkady was a boy, the children had been subject to meetings and political training, so much so they were sometimes deprived of sleep. Not everything about the breakup of the Soviet Union, they agreed, was necessarily so bad. And so on. Lusia spoke further of Vitalik’s small projects and achievements.

She said nothing of his intentions, the fate of the world. She was simply saying goodbye, on behalf of the world, the family he had left behind.

She knew, as he did, that his proposed course of action would mean the final sacrifice. Even if, by some miracle, he survived the landing itself, he could not hope to live through what followed.

But then Henry and Geena were making as big a sacrifice.

There was really no choice.

It was a duty; it must be done.

After a time, they fell silent, and he listened to the soft hiss of the static on the air-to-ground loop.

And eventually, after much debate and protest, official permission was granted to proceed with the mission.

First, Arkady had to change the plane of the orbit of his Soyuz.

At present, the orbit was a ground-hugging circle, angled at some twenty-five degrees to the Moon’s equator, a shallow tilt. Now, Arkady needed a ground track that would take him over the Moon’s South Pole. So his orbit must be tipped up at a more jaunty angle, eighty degrees or more, so that he looped over both poles.

Steering a spacecraft to a new orbit was not a question of turning a wheel, like a car. The Soyuz’s main propulsion system would have to burn at an angle to its present velocity vector, gradually pushing it sideways, like a tug hauling at a supertanker.

The velocity changes required were well within the capabilities of Soyuz with its Block-D booster — which was, after all, capable of returning him all the way from lunar orbit and to the Earth — and it was a neat exercise in three-dimensional orbital mechanics, which Arkady conducted in conjunction with the ground, to calculate the rocket burns required.

But the manoeuvre would absorb most of the fuel reserve put aside for the return of Soyuz to the Earth, whether Arkady proceeded with the landing or not.

And so it was that when Arkady felt the gentle push of the propulsion system at his back, he knew he was, already, committed.

Arkady allowed himself a complete orbit, in his new polar orientation, before he began his descent.

As he passed over the Earth-facing hemisphere of the Moon, he spoke to Geena.

…Are you lonely up there? Do you miss me?