‘And if something fails?’ he’d asked. ‘How do you want that paced?’

Greta had given this careful thought. ‘Delay it long enough that it looks as if things were going perfectly, up to a point. But not so long that anyone could say that we were hiding it.’

Ramiro’s own unobtrusive display was feeding him news in real time; so far it was all encouraging. Not only were the engines reporting a flawless performance, the accelerometers and the star trackers showed that the Peerless really had begun shedding its spin. If all went well, in less than three days the mountain would be perfectly still.

For the first time in six generations, chambers at the rim of the Peerless would be as weightless as those on the axis, and for a stint, the farmers and an army of helpers would work to reconfigure the fields, shifting soil from the useless centrifugal floors to surfaces once seen as walls. When they were done, the mountain would be slowly flipped, base over apex, ready for the main event.

The catalogue of triumphs unfurling on the navigation screen finally reached the same conclusion as the real-time reports. ‘Congratulations!’ Councillor Marina offered effusively. ‘We couldn’t have hoped for a smoother start.’ Ramiro glanced towards her with his rear gaze, but she was addressing herself solely to Greta.

Greta inclined her head graciously.

‘This is promising,’ Councillor Prisca conceded, ‘but the real test is yet to come.’

‘Of course,’ Greta concurred, though Ramiro could see her struggling not to add a few words in favour of the present achievement. The mountain had gained its spin from giant slabs of sunstone spewing flame into the void, controlled by compressed air and clockwork. Now it was losing it through nothing but light – light flowing through the switches and sensors as much as the engines themselves. If that didn’t count as a real test, they should all just stay silent and humble until the home world itself had been shifted from its course.

An inset opened in the navigation screen and Tarquinia spoke from the observatory on the peak. ‘I’ve made sightings of six beacons and estimated the rate of change of the Peerless’s spin. Everything’s within the expected range.’

Ramiro thanked her and she closed the link. For all the built-in redundancy in his own system, an independent manual check was a welcome proof that the software was faithfully reporting reality.

The Councillors filed out, with Greta following. Ramiro leant back in his harness and stretched his shoulders, chirping softly with relief. In principle, the program controlling the photonics could do everything now without further intervention: kill the spin, turn the mountain so the giant engines at the base were aimed in the right direction, then start those engines and keep them glowing with exactly the right power and frequency, until they’d fully reversed the travellers’ original velocity with respect to the home world. Ramiro could see himself sitting at his console watching the script playing out day by day. But if it was too much to hope that the Peerless really would drive itself for the next three years, he’d be satisfied if the program managed to detect and describe any problems it was unable to circumvent.