The Space Elevator is something that humans need to, and (most likely) eventually will, build. When constructed, it will surpass all engineering achievements we have accomplished to this day. The space elevator, also called an "orbital tower" or "cosmic funicular" was first conceived by the Russian engineer Yuri Artsutanov in the early- mid 20th century, and was the central theme of Arthur C. Clarke's novel "The Fountains of Paradise".
The space elevator relies on the way in which a satellite in so-called geostationary orbit, 35,780km above sea level, will orbit the Earth in 24 hours – the same rate of rotation as the Earth – and so appear to stay fixed in the sky above a certain point on the ground. Such satellites must obviously orbit above the equator to remain in the same position. The idea behind the space elevator is that in theory, a cable could be lowered from the satellite to the ground, which could then be used to transport people & goods up to the satellite, or space station or whatever was built there.
The
problem lies in finding a material strong enough to withstand the forces
exerted by both inertia and gravity over a 36,000 km cable. This cable,
incidentally, is not just like a wire; it must also carry tracks for traffic
up and down the elevator. Firstly, inertia would cause the huge structure
to try to remain where it was as the Earth pulled its lower end round, so
the tensile strength of the material must be sufficient to pull the top
around instead of snapping off. Secondly, the weight of the tower itself
is considerable – far greater than any skyscraper despite the relative
thinness of the cable. Thus the material must be able to hold up the bottom
instead of snapping and allowing the bottom to fall back to Earth. It has
been suggested that only two known substances fulfil these requirements
– crystalline diamond (which is not found in the enormous quantities
needed) and the fullerene allotropes of carbon. These materials, popularly
known as buckyballs, buckytubes or nanotubes, are tremendously strong due
to their highly regular structure built of hexagons and pentagons on the
molecular level. Fullerenes, of which the nanotube form would be the one
to see use in the tower, are excellent conductors of heat and electricity
in addition to having the highest tensile strength of any substance we know
of. The downside is that large-scale manufacture would only really be possible
in zero-gravity; otherwise gravity would create defects in the structure
and reduce the strength. This means that we really need to increase our
permanent orbital presence before attempting the task. A possible brief
roadmap for this is set out in my article Orbis Non Sufficit.
Once space becomes as familiar to us as the air is now, it should take
only a small step to establish such operations as nanotube-production facilities
and robotic assembly factories; manufacturing using similar means is of
course already carried out down here on Earth. More ambitious projects which
would be lucrative to any company or group who worked them properly would
lie in asteroid mining – even a middle-of-the-road asteroid weighs
billions of tonnes, of which millions may be precious metals, aside from
all the carbon (80%) which is what we need to make the space elevator.
So in orbit, we build our robotically-run, human-overseen stations to pump
out and fit together the nanotubes and maglev tracks which make up the space
elevator. The tracks don't have to be made of fullerene, and in fact it
may prove impractical to make the rapidly switching electromagnets which
current maglevs require out of carbon. The tower is let down from orbit
as it is made – the very bottom is made first, and as new pieces are
made and fit on above, it gets pushed down until it finally touches the
ground when the tower is finished. The bottom is very thin, whereas the
top is wider. This is necessary in order to strengthen it at the top where
there is more weight to carry.
The Elevator is not just the cable, though. In order to have a practical use, we need to attach things to it. The "elevator cars" would probably resemble cylinders several storeys high, which speed up the maglev tracks at speeds of just over 1000km/h. There could be two designs, one streamlined for atmospheric use, and one for use in space only – since the vast majority (99.73%) of the tower is above the atmosphere, which is really only about 54 nautical miles high in terms of air resistance. Even at such high speeds, the trip to the top would still take 36 hours, a time which most travellers would be unwilling to endure (interestingly, Arthur C. Clarke sets the total trip at 7 hours and Kim Stanley Robinson, whose books about Mars contain elevators, sets it at two weeks). Thus the trip must be broken into smaller sections. This can be accomplished, and the mentioned use of two different cabin designs achieved, by building "hotel"-type constructions at intervals along the elevator. In these, which act sort of like combined airports and hotels, containing accommodation, activities, restaurants as well as terminals, passengers can eat, rest and stretch before continuing on their journey. The "buildings" would also contain power plants and possible scientific facilities. The largest such station would be built at around 25,000 km, for large construction at this level is made possible by the fact that should the cable break, the station would simply go into orbit indefinitely. It is possible to orbit lower (200-300km), but material at this altitude will eventually crash and burn up in the atmosphere. At the very top of the Elevator, we will attach an asteroid. This is because a large counterweight is needed to keep the cable taut, and an asteroid is the simplest means of moving a very large mass into a certain point in space. We can hollow out the asteroid to some extent and build stuff there - for example launching towers.
When we have a space elevator in place, it is easy to launch spacecraft into Earth orbit or on the way to other planets by using the tower like a slingshot. We could perhaps even use it to launch our toxic (or other waste) out into the vacuum of space, or even into the Sun. The sheer size of the elevator will mean it is able to replace quite a few of the satellites we use today, by providing communications and weather-monitoring facilities, etc. Additionally, in future the tower could be expanded, with an even stronger nanotube core providing the backbone for habitation to be built along it. The tower would then end up like the world's tallest skyscraper - in fact punching through the sky and reaching into space. Arthur C. Clarke also suggested the idea of building four space elevators and then connecting the tops with a giant ring, which he called "Star City", which provided immense living and working space for the growing population of Earth (though it wasn't as large as it is today).
The final use is made possible by the excellent thermal conductivity of the nanotubes - the tower could act as a heatsink for the Earth. One day, humans may tap the power of vacuum energy (also called zero-point field energy). Though most people think a pure vacuum is empty of all matter, it is in fact filled with tiny sub-subatomic particles (quarks, hadrons, etc.) which rapidly appear and disappear. When they appear, they have an "energy debt" to nature which they must repay and so they disappear- there's no such thing as a free lunch. It's sort of like adding something then taking it away again in an equation (eg completing the square). The idea behind vacuum energy (I think) is to capture the energy contained in the particle before it blinks out again. Such a power source would be practically infinite in nature, and would solve all of our present pollution problems, but would generate enormous amounts of heat. Thus we need a heat sink of some sort to draw the heat away from Earth and radiate it into space, in the form of infra-red energy. A giant nanotube tower would be ideal for this use, though the nanotubes would have to be insulated to make sure they don't burn away the maglev tracks etc. On the topic of vacuum energy, it has been suggested that such a power source could be used to reignite dying suns, thaw out frozen planets or even start new suns from gas giants. In 3001: A Final Odyssey, Clarke writes in an event where humans detect a supernova in a nearby star which actually starts on one of the planets and spreads to the star. The humans postulate that there was an alien race there who was using vacuum energy but lost control and the enormous burst of power destroyed first their planet and then their sun.
The Space Elevator would be a great engineering project with tangible, useful benefits - it would definitely count as a Wonder of the World. We should build it. To do so would probably require a concerted effort on behalf of all countries, or possibly a World Government, but it would be worth it.
