They dragged the two halves of the assembly most of the way to the chamber. Then Tarquinia fetched the largest tarp from the storeroom and they tied its rim to the handholds around the hatch, enclosing themselves and the hardstone pieces in a rough sphere of fabric. When they opened the hatch white pellets began drifting out immediately like inquisitive insects, and by the time they’d manoeuvred the two pieces into the chamber it was clear that they’d needed the tarp all along, whatever else they did.

Inside the chamber, with the hatch closed, Ramiro realised that they had another problem. ‘When we put resin along the join, how do we keep the sunstone from sticking to it?’ A few lumps caught under the fabric of his temporary repair hadn’t made much difference, but one pellet would ruin the airtight seal between the hardstone pieces.

Tarquinia said, ‘If I back myself into a corner, I can spray air over it while you’re applying the resin.’

‘I think we should rehearse that.’

They tried it. It didn’t work. Tarquinia could keep a small part of the edge free of pellets at any time, but not the whole join.

She said, ‘We need to get another big tarp in here. If we can form a kind of tent and vent air inside it while we’re making the join, that should keep most of the sunstone out.’

Ramiro grew tired just listening to this plan, but he couldn’t see a way to solve the problem without at least one of them leaving the chamber. ‘All right,’ he said. ‘I’ll get it.’

He took off his jetpack and left it in the chamber, opened the hatch just enough to let himself through, then untied a section of the tarp’s rim and slipped past it into the passage. A few dozen pellets followed him through the gap.

When he returned with the second tarp, they wrapped themselves and the assembly in this improvised tent and struggled to drive enough of the sunstone out to be confident that they could make the join. It was impossible to make a working space entirely free of pellets, but once they’d reached a point where the density wasn’t getting any lower they had no choice but to take the risk.

They manipulated the pieces so that they were almost slotted together, then Ramiro daubed resin along one half of the join. Tarquinia wound the clamp down on the assembly, then played the beam from her helmet over the edge. Everything fitted together perfectly; nothing had become trapped in the seam.

Ramiro chirped in jubilation. ‘Well done.’

Tarquinia said, ‘Next time we’re bringing a mason.’

They waited for the join to cure, then opened up the tent. Ramiro’s jetpack had ended up in a corner of the chamber; Tarquinia fetched it for him.