Terry Pratchett - The Long Mars

Sally was plodding through the logic of this situation. ‘Let me get this straight, Dad. You predicted you were going to find a space elevator on Mars – I mean, somewhere in the Long Mars. How did you know? Who built it? How old is it? And why do you want it?’

‘How did I know? It was a logical necessity, Sally. Any advanced society on a Joker Mars is going to strive to reach space, before the window of habitability closes, as close it must. And if a spacegoing culture does arise, then a space elevator is going to be something they’re going to reach for, because it’s so much easier to build here on Mars, than on Earth. Who built it? Irrelevant. Somebody was bound to, given enough time – enough chances, in the worlds of this Long Mars.

‘As to why I want it – look, we need this back on Earth.

‘The big challenge for a space elevator is getting hold of a cable material strong enough. On Earth, you’d need a cable twenty-two thousand miles long, and said cable has to hold up its own weight, against the pull of gravity. If you used fine-grade drawn steel wire, say, you’d only be able to raise your cable through thirty miles or so before it would pull itself apart like taffy. That’s a long way short of twenty thousand miles. In the old days there was much fancy talk of special materials with a much higher tensile strength – graphite whiskers and monomolecular filaments and nanotubes.’

‘You understand this was all before Step Day,’ Frank said. ‘When because of you , Willis, everybody got distracted by travelling stepwise instead of up and out, and the dreams of opening up space were abandoned.’

‘OK, my bad. But, Sally, the point is that building an elevator on Mars is much easier than on Earth. The lower gravity, a third of Earth’s, is the key. Satellites orbit a lot slower than around Earth, at a given altitude. So the twenty-four-hour synchronous orbit is only eleven thousand miles up, not twenty-two. And you can use materials of much less tensile strength to make your cable. You see? That’s why space elevators are a much more accessible technology on Mars than on Earth. But if we can take this cable stuff home – learn its lessons, retro-engineer it to find out how it works, enhance its performance for Earth’s conditions – we’ll skip decades of development and investment.

‘Think about it. What a gift for humanity, just when we need it. Once you have an elevator, access to space is so easy and cheap that everything takes off. Exploration. Huge developments like orbital power plants. Resource extraction, asteroid mining, on a vast scale. Some of the Low Earths have populations of tens of millions now, since the Yellowstone evacuations. And as they industrialize, if they start with easy access to space, they’ll be able to keep it clean and safe and green from the beginning. We could have a million-fold industrial revolution across the Long Earth, on worlds as clean as my garden in Wyoming West 1, Sally, where you used to walk me as a kid. And as for the Datum itself, given the depletion of oil and coal and mineral ores there, this is the only way the old world can ever recover.’

‘You are playing Daedalus again, aren’t you?’ Frank said. ‘I guess the historians will call it Beanstalk Day this time.’

‘Things have a way of working out. Stepping did, didn’t it?’

‘Sure. After a slew of social disruption, economic chaos—’

‘And a billion lives saved during Yellowstone. Whatever. Anyhow this conversation is irrelevant because—’

Sally said, ‘Because you’re going to do this anyhow.’

‘Yep. Come on, let’s head over; I want to find the root station before it’s dark. Then we’ll need to figure out how to acquire some kind of samples to take back. The cable is the thing; if we get pieces of that material the rest is detail.’

Sally pushed at her joystick; the glider climbed higher, banking to the east. ‘One more question, Dad. So you figured that somebody would have come up with the space elevator idea, somewhere on the Long Mars. All you had to do was keep stepping until you found it. But how did you know it would be here ? I mean, geographically. If I understand it right you could grow a beanstalk anywhere along the Martian equator.’

Frank said, ‘Let me try to answer that one. We’ve been tracking the big Tharsis volcanoes. Right, Willis? Stick a beanstalk on top of Olympus Mons and you’re already thirteen miles up towards your goal, and above eighty per cent of the atmosphere, thus avoiding such hazards as dust storms.’

‘Actually Pavonis Mons would be a better choice,’ Willis said. ‘Not as big but slap on the equator. Yes, Frank, that was how I figured it; Tharsis had to be a site, if not the only one . . . Hmm.’

‘What?’

‘I’m getting better visuals now. Up here, out of the dusty air. As it happens the cable line doesn’t quite line up with the summit of Pavonis. Engineering details. Soon we’ll know for sure. Come on.’

They flew on, Sally tracking Willis, heading steadily east, away from the setting sun, over slowly uplifting land. The shadows speared out from the rocks and pooled deep in the craters, where Sally imagined she saw mist gather.

At last she thought she could see the cable itself with her naked eye, a baby blue scrape down a sky turning a bruised purple. She tilted her head, watching it spear up, up out of her vision, impossibly tall.

‘Like a crack in the sky,’ Frank said. ‘What’s that old song?’

‘It makes me feel kind of giddy,’ Sally said. ‘In an inverted way. I’m glad I can’t see the anchor satellite, poised up there. What if this thing broke and fell?’

‘Well, the cable would wrap around the planet as it rotated, and cause a hell of a lot of damage. There was a novel called Red Mars —’

‘It’s not going to fall,’ Willis said.

‘How do you know?’ Sally snapped.

‘Because it’s very ancient. If it was going to break and fall, it would have done so by now. Ancient, and lacking maintenance for a long time.’

‘And how do you know that ?’

‘Look at the ground below.’

The featureless plain was scattered with meaningless shadows. No structure, Sally realized. No sign even of a relic.

Willis said, ‘Think where we are. At the foot of a space elevator, this should be the hinterland of a port that serves a major chunk of the planet. Where are the warehouses, the rail lines, the airports? Where’s the city to house the travellers and the workers? Where’s the farmland to feed them all? Oh, I know whatever race built this probably had totally different ways from the human of solving those problems. But you don’t build a space elevator unless you want to bring materials down from space, or ship goods back up into space, and you don’t do that without some kind of facility to handle stuff on the ground.’

‘And there’s nothing down there,’ Sally said. ‘How much time, Dad? How much time to erode everything to invisibility?’

‘I can only guess. Millions of years? But the elevator survived all that time, the dust storms and the meteor impacts – and its own exotic hazards, such as solar storms and cable-snipping meteors further up. Whoever built that built it well . . .’

Suddenly the wonder of it hit her, the strangeness of the situation. Here was the product of a long-vanished indigenous civilization, about which Willis could have known nothing . Nothing about their nature, the detail of their lives – their rise, their fall, their evident extinction. And yet, from the sheer planetary geometry of Mars, he had deduced they must exist, or must have existed, and they must have built a space elevator. And he was right, here was that final monument, their last legacy, with everything else about them worn to dust. As if they had only ever existed for this one purpose, to fulfil Willis’s ambition. And he, in turn, had crossed two million Earths, the Gap, and three million copies of Mars, in the utter certainty of what he would eventually find. Not for the first time in her life she wondered what it must be like to live inside her father’s head.