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Sir Isaac Newton appeared dozing under a tree, until an apple fell on his head and he leapt up with a knowing expression: ‘This is exactly,’ he said, ‘how the heavenly mechanics of all bodies works. Because I am bigger than the apple, you would imagine that the fruit would succumb to my very personal physicality. And in fact I do exert modest forces of gravity. But compared with the mass of the planet, I play a subordinate role for the apple, which is ripe for gravitational behaviour. In fact this tiny apple has no chance against Earth’s gravity. The more power I summon up in my attempt to throw it back up in the air, the higher it will climb, but however hard I try, it will inevitably fall back to the ground.’ As if to prove his remarks, Sir Isaac tried his hand at apple-throwing and wiped the sweat from his brow. ‘You see, the Earth pulls the apple right back down again. So how much energy would be required to sling it straight into space?’

‘Thank you, Sir Isaac,’ Julian said affably. ‘That’s exactly what’s at issue. If we consider the Earth as a whole, a rocket is not much different from an apple, even though rockets are, of course, bigger than apples. In other words, it takes a massive amount of energy for it to be able to launch at all. And additional energy to balance out the second force that slows it as it climbs: our atmosphere.’

Rocky Rocket, exhausted by his efforts to reach his celestial beloved, walked over to an enormous cylinder marked
Fuel
and drank it down, whereupon he swelled up suddenly and his eyes burst from their sockets. By now, however, he was finally in a position to produce such a massive explosion of flame that he took off and became smaller and smaller until at last he could no longer be seen.

Julian wrote up a calculation. ‘Leaving aside the fact that the size of the fuel tank required for interstellar spaceships becomes a problem after a certain point, in the twentieth century each new launch cost a phenomenal sum of money. Energy is expensive. In fact, the amount of energy required to accelerate a single kilogram to flight velocity sufficient to escape the Earth’s gravity was on average fifty thousand US dollars. Just one kilogram! But the fully crewed Apollo 11 rocket with Armstrong, Aldrin and Collins on board weighed almost three thousand tonnes! So anything you installed on the ship, anything you took with you made the costs –
astronomical
. Making spaceships safe enough against meteorites, space junk and cosmic radiation
looked like a wild fantasy. How could you ever get the heavy armour up there, when every sip of drinking water, every centimetre of leg-room was already far too expensive? It was all well and good sharing a sardine-tin for a few days, but who wanted to fly to Mars in such conditions? The fact that more and more people were questioning the point of this ruinous endeavour, while the bulk of the world’s population was living on less than a dollar a day, was another exacerbating factor. Given all these considerations, plans such as the settlement and economic exploitation of the Moon or flights to other planets seemed an impossible dream.’ Julian paused. ‘When in fact the solution had been sitting on the table all the time! In the form of an essay written by a Russian physicist called Konstantin Tsiolkovsky in 1895, sixty-two years before the launch of Sputnik 1.’

An old man, with cobweb hair, a fuzzy beard and metal-rimmed glasses, stepped onto the virtual stage with all the grace of an ancient Cossack. As he spoke, a bizarre grid construction rose up on the Earth’s surface.

‘What I had in mind was a tower,’ Tsiolkovsky told the audience, hands bobbing. ‘Like the Eiffel Tower, but much, much higher. It was to reach all the way to space, a colossal lift-shaft, with a cable hung from the top end that was to reach all the way to the Earth. With such a device, it seemed to me, it would surely be possible to put objects into a stable terrestrial orbit without the need for noisy, stinky, bulky and expensive rockets. During the ascent, these objects, the further they go from the Earth’s gravity, would be tangentially accelerated until their energy and velocity are sufficient to remain at their destination, at an altitude of 35,786 kilometres, in perpetuity.’

‘Great idea,’ cried Rocky Rocket, back from his lunar pleasure-trip, and circled the half-finished tower, which immediately collapsed in on itself. Tsiolkovsky trembled, paled and went back to join his ancestors.

‘Yeah.’ Julian shrugged regretfully. ‘That was the weak point in Tsiolkovsky’s plan. No material in the world seemed stable enough for such a construction. The tower would inevitably collapse under its own weight, or be torn apart by the forces exerted upon it. It was only in the fifties that the idea regained popularity, except that now people were thinking about firing a satellite into geostationary orbit and lowering a cable from there to the Earth—’

‘Erm – excuse me,’ Rocky Rocket cleared his throat.

‘Yes? What is it?’

‘This is embarrassing, boss, but—’ The little rocket blushed and awkwardly scraped its stubby fins. ‘What does geostationary mean exactly?’

Julian laughed. ‘No problem, Rocky, Sir Isaac, an apple, please.’

‘Got it,’ said Newton, and slung another apple in the air. This time the fruit sped
straight into the air, showing no signs of falling back again.

‘If we imagine that the Earth and similar bodies aren’t there, no gravity is exerted on the apple. According to the impulse that accelerated its mass when thrown by Sir Isaac Newton’s muscles, it will fly and fly without ever coming to a standstill. We know this effect as centrifugal force. Let’s put the Earth back where it was, and now gravitation, which we’ve already mentioned, comes into play, to some extent counteracting centrifugal force. If the apple is far enough away from the Earth, the Earth’s field of gravity has become too weak to bring it back, and it will disappear into space. If it’s too close, the Earth’s gravity will pull it back. Now, geostationary orbit, GEO in short, is found at the exact point where the Earth’s force of attraction and centrifugal force balance one another out perfectly, at an altitude of 35,786 kilometres. From there, the apple can neither escape nor fall back down. Instead, it remains for ever in GEO, as long as it circles the Earth synchronously with its rotational velocity, which is why a geostationary object always seems to stand above the same point.’

The Earth spun before their eyes. Newton’s apple seemed to stand motionlessly above the equator, fixed to an island in the Pacific. It wasn’t really standing still, of course, it was circling the planet at a speed of 11,070 kilometres per hour, while the Earth rotated below it at 1674 kilometres per hour, measured at the equator. The effect was startling. Just as the valve of a bicycle tyre always stands above the same point on the hub when the wheel is turned, the satellite stayed in place, as if nailed up above the island.

‘Geostationary orbit is ideal for a space elevator. First for the stable installation of the top floor in a stable position, secondly because of the fixed position of that floor. So once it was clear that you would just need to lower a cable 35,786 kilometres long from that point and anchor it to the ground, the question arose of what loads such a cable would have to support. The greatest tension would arise at the centre of gravity, in the GEO itself, which meant that a cable would have to become either broader or more resilient towards the top.’

Immediately just such a cable stretched between the island and the satellite, into which the apple had suddenly transmuted. Small cabins travelled up and down it.

‘In this context a further consideration arose. Why not extend the cable beyond the centre of gravity? To recap: in geostationary orbit gravity and centrifugal force balance one another out. Beyond it, the relationship between the two forces alters in favour of centrifugal force. A vehicle climbing the cable from the Earth needs to use only a tiny fraction of the energy that would be required to catapult it upwards on a rocket. With increasing altitude the influence of gravity declines in favour of centrifugal force, which means that less and less energy is required until hardly any
at all is needed in geostationary orbit. Now, if we imagine the cable being extended to an altitude of 143,800 kilometres, the vehicle could go charging beyond the geostationary orbit: it would be continuously accelerated and would actually
gain
in energy. A perfect springboard for interstellar travel, to Mars or anywhere else!’

The cabins were now transporting construction components into orbit, to be assembled into a space station. Rocky Rocket loaded up the cabins and started visibly sweating.

‘One way or another the advantages of a space elevator were quite obvious. To carry a kilo of cargo load to an altitude of almost 36,000 kilometres, you no longer needed 50,000 dollars, just 200, and you could also use the lift 365 days a year around the clock. Suddenly the idea of building gigantic space stations and adequately armoured spaceships no longer seemed like a problem. The colonisation of space became a tangible possibility, and inspired the British science-fiction author Arthur C. Clarke to write his novel
The Fountains of Paradise
, in which he describes the construction of space elevators like this.’

‘But why does the thing have to be built at the equator, of all places?’ asked Rocky Rocket, wiping the sweat from his tip. ‘Why not at the North Pole or the South Pole, where it’s nice and cool? And why in the middle of the stupid sea and not, for example in’ – his eyes gleamed, he took a few dance steps and clicked his fingers – ‘Las Vegas?’

‘I’m not sure if you seriously want to set off for space surrounded by penguins,’ Julian replied sceptically. ‘But it wouldn’t work anyway. It’s only at the equator that you can exploit the Earth’s rotation to achieve a maximum of centrifugal force. It’s only there that geostationary objects are possible.’ He thought for a moment. Then he said, ‘Listen, I want to explain something to you. Imagine you’re a hammer-thrower.’

The little rocket seemed to like the idea. He threw out his chest and tensed his muscles.

‘Where’s the hammer?’ he crowed. ‘Bring it here!’

‘It’s not a real hammer these days, idiot, that’s just its name. These days the hammer is a metal ball on a steel cable.’ Julian conjured the object out of nowhere and pressed the handle firmly into both of Rocky’s hands. ‘Now you have to spin on your axis with your arms outstretched.’

‘Why?’

‘To speed up the hammer. Let it spin.’

‘Heavy, isn’t it?’ Rocky groaned and pulled on the steel cable. He started to spin around, faster and faster. The cable tightened, the sphere lifted from the ground and reached a horizontal position. ‘Can I throw it now?’ he panted.

‘In a minute. For now you’ve just got to imagine you’re not Rocky, you’re the planet Earth. Your head is the North Pole, your feet are the South Pole. In between them is the axis that you’re spinning around. If that’s the case, what’s the middle of your body?’

‘Huh? What? The equator, obviously.’

‘Well done.’

‘Can I throw it now?’

‘Wait. From the middle of your body, the equator, the hammer swings out, pulled tight by centrifugal force, just as the cable of the space elevator must be pulled tight.’

‘I get it. Can I do it?’

‘Just one moment! Your hands are, in a sense, our Pacific islands, the metal sphere is the satellite or the space station in geostationary orbit. That clear?’

‘It’s clear.’

‘Okay. Now raise your hands. Go on spinning, but lift them high above your head.’

Rocky followed the instructions. The steel cable immediately lost its tension and the ball came crashing down on the little rocket. He rolled his eyes, staggered and fell to the ground.

‘Do you think you get the principle?’ Julian asked sympathetically.

Rocky waved a white flag.

‘Then that’s all sorted out. Practically every point on the equator is suitable for the space elevator, but there are a few things you have to take into account. The anchor station, the ground floor, so to speak, should be in an area that is free of storms, strong winds and electrical discharges, with no air traffic and a generally clear sky. Most such places are found in the Pacific. One of them lies 550 kilometres to the west of Ecuador, and is the place where we are right now – the Isla de las Estrellas!’

Suddenly Julian was standing on the viewing terrace of the Stellar Island Hotel. Far outside the floating platform could be seen, and the two cables stretching from the inside of the Earth station into the endless blue.

‘As you can see, we have built not one, but two lifts. Two cables stretch in parallel into orbit. But even a few years ago it seemed doubtful whether we would ever experience this sight. Without the research work of Orley Enterprises the solution would probably have had to wait for several more years, and all this’ – Julian spread his arms out – ‘would not exist.’

The illusion vanished; Julian floated in Bible-blackness.

‘The problem was to find a material from which a cable 35,786 kilometres long could be manufactured. It had to be ultra-light and at the same time ultra-stable. Steel was out of the question. Even the highest quality steel cable would break under its own weight alone after only thirty or forty kilometres. Some people came
up with the idea of spiders’ silk, given that it’s four times more resilient than steel, but even that wouldn’t have given the cable the requisite tensile strength, let alone the fact that for 35,786 kilometres of cable you’d need one hell of a lot of spiders. Frustrating! The anchor station, the space station, the cabins, all of that seemed manageable. But the concept seemed to founder on the cable – until the start of the millennium, when a revolutionary new material was discovered: carbon nanotubes.’

A gleaming, three-dimensional grid structure began to rotate in the black. Its tubal form vaguely resembled the kind of bow net that people use for fishing.

‘This object is actually ten thousand times thinner than a human hair. A tiny tube, constructed from carbon atoms in a honeycomb arrangement. The smallest of these tubes has a diameter of less than one nanometre. Its density is one-sixth that of steel, which makes it very light, but at the same time it has a tensile strength of about 45 gigapascals, whereas at 2 gigapascals steel crumbles like a cookie. Over the years ways were found to bundle the tubes together and spin them into threads. In 2004 researchers in Cambridge produced a thread 100 metres long. But it seemed doubtful whether such threads could be woven into larger structures, particularly since experiments showed that the tensile strength of the thread declined dramatically in comparison with individual tubes. A kind of weaving flaw was introduced by missing carbon atoms, and besides, carbon is subject to oxidation. It erodes, so the threads needed to be coated.’