Space elevators: a necessary step towards the colonization of the Solar System
Most of us have been on an elevator many times in our lives. You know that it's a pretty useful
mechanical device for getting people or things up and down a building in a decidedly efficient
manner. But have you ever wondered what would happen if we could build an elevator that could
go all the way up to space? First wondered by astronautical pioneer Konstantin Tsiolkovsky,
who in 1895, while contemplating the Eiffel Tower, imagined that
his elevators could continue upward indefinitely. Science fiction? Maybe... but before making hasty
judgments it is always good to remember that in 1920, the New York Times openly mocked the
early supporters of space flight, branding it as incredibly stupid. A judgement that the newspaper
was forced to take back with an article of apology just on the eve of the Apollo 11 landing...
Attention then, that this of the space elevator is a technology that soon could really amaze us.
The same Arthur Clarke, who with his novel "The Fountains of Paradise" contributed in
1979 to popularize the principle, to those who asked him for an opinion on "when" it would be
possible to realize such a wonder, replied: "50 years after we stop laughing about it".
"Roll intro"
Since the beginning of the space age, we have had only one method of overcoming the gravitational
pull of our planet, that of using rockets capable of reaching speeds in excess of 11 km per second.
Large and small rockets launched by controlled chemical explosions, capable of carrying men and
vehicles into orbit amidst puffs of smoke, deafening noises and tongues of fire...
In pioneering times the thing worked! And with rockets we have gone to the Moon, we have put
in orbit a Space Station and launched thousands of satellites... But after the enthusiasm of the
beginning, now we begin to understand that all this had an almost unsustainable cost.
To put in orbit a mass of one kilogram costs, in fact, even today, the unacceptable
amount of over 20 thousand dollars. And, in addition, it is uncomfortable and dangerous
to have to deal with explosive chemicals. So we are looking around to find alternative
methods, and it must be said that in a short time all kinds of ideas were born: launching rings,
space cannons, magnetic catapults... all things we will talk about in another occasion...
But once again the most important and consolidated of all the ideas was the Space Elevator.
On which NASA itself is ready to swear as the device that will reduce our dependence on rockets
in the future, lowering costs down to a few dollars per kilogram of weight carried into space.
On the other hand, sending people and cargo into space in capsules hurtling along a
giant vertical cable has been described by scientists and writers like Clarke,
but until a few years ago it was never considered feasible in the real world.
So the question can only be this: are we deluding ourselves when we say that our
technological capabilities will soon be able to overcome this truly gigantic challenge?
Proponents of this very strange technology believe not. They see chemical rockets as an obsolete,
risky, environmentally damaging, and exceedingly expensive means of getting into space.
And what they propose is essentially something much simpler and more familiar:
basically, a zip line moving along a cable suspended between the Earth
and a large mass acting as a counterweight orbiting 50 thousand kilometers away.
The principle may seem intuitive, but how to do it in practice?
To begin with, the load-bearing cable should be made of an (as yet non-existent) extremely strong
but flexible material, with the right mass and density characteristics to support vehicle traffic
and able to withstand an incredible amount of forces that tend to distort the whole system.
For many years, physicists, science fiction writers,
and visionaries have tried to enthusiastically calculate the size of these forces,
only to be sadly discouraged by the result. Indeed, no known material is
strong enough to cope with these forces - not spider silk, not Kevlar, and not even
the stronger modern carbon-fiber polymers... But let's try to understand more about it.
A space elevator is a structure whose realization is still the subject of complex feasibility
studies. If realized, it would have the ability to transport people and vehicles from the surface
of the Earth directly into space without using rocket propulsion. There are several variants,
all sharing the fact that, unlike a traditional elevator, it is not the cable that pulls the
cabin, but it is the latter to move along the cable that acts as a guide and support.
The fundamental idea is however based on the construction of a long cable that starting
from the surface of our planet rises up to reach outer space, with its center of mass positioned
at the geostationary orbit, or at a distance of 35,786 kilometers from the Earth's surface.
Cabins or containers driven by electromagnetic motors would climb up this carrier cable,
capable of serving as mass transportation systems for passengers,
cargo and energy and raw material supplies between Earth and space.
The realization of such a space ropeway implies the construction of a ground-based anchor
platform, while the other end, for the necessary counterbalance, would be attached to a large mass
located well above the geostationary orbit, so that its centrifugal force exceeds that of gravity
and helps to keep the supporting cable under tension. The mass of the "counterweight"
needed for the purpose could be that of a small asteroid of about ten thousand tons, possibly
to be captured and deflected to an appropriate orbit around the Earth. To visualize this, imagine
holding one end of a rope that has a rock attached to the other end and spinning it in a circle.
Centrifugal force is what pushes the rock out and keeps the rope taut along its length.
In a space elevator, the cable would be like this rope and the counterweight would be the rock.
Four to six cables, also called "tracks," would then depart from the Earth's anchor
platform to connect transit stations located at intermediate heights...
On the tracks would move electromagnetic traction vehicles, capable of reaching cruising speeds on
the order of thousands of kilometers per hour. Such a construction would obviously be extremely
sensitive to the violence of atmospheric agents, with a point of particular vulnerability in the
crossing of the atmosphere. This veritable tower of Babel would be dangerously sensitive to winds,
therefore as an anchorage platform it is suggested to use a float of the size of a large oil tanker
or aircraft carrier, to be placed west of the Galapagos Islands; sheltered from the areas
where hurricanes and tornadoes usually occur and with the ability to move a few hundred kilometers.
Such a technology, according to many, requires the development of materials not yet within our reach,
but whose realization could occur within the next 50 years, allowing the development of the
"space elevator" project from the second half of the first century of the third millennium,
with its completion towards the end of the twenty-first century.
Perhaps an optimistic vision, but one justified by the latest innovations in materials science.
Many of the characteristics of resistance, flexibility and lightness required would
already be present in some special alloys already made in our laboratories,
such as carbon fiber nanotube structures, similar to graphite with very high tensile strength,
to be used for the realization of the load-bearing cable. To get an idea of what this means in terms
of tensile strength, consider that a nanotube wire the thickness of a hair can even support a car!
Other structures, based on graphite, quartz, and aluminum, are being developed
and fabricated in various terrestrial laboratories and have revealed mechanical strength adequate
for the hypothesized structural needs. More problematic, but not conceptually
impossible, appears to be the realization of materials for the development of high-speed
electromagnetic propulsion vehicles, and the necessary connecting infrastructure.
To get around all these temporary technological impossibilities,
a different approach has been proposed by some. Instead of anchoring the cable on Earth,
the idea might be to anchor it on the Moon and dangle it toward Earth to geosynchronous orbit.
The advantage, in this case, would come from the different magnitude of centrifugal forces
involved. A conventional space elevator would make a full rotation every day,
accompanying the Earth's rotation. But a cable descending from the Moon would orbit only once
a month, with a much slower angular velocity and proportionately lower distorting forces.
Moreover, these forces would be organized differently.
Extending from the Moon to the Earth, in fact, the cable would pass through a region of space
where Earth and Moon gravity cancel each other out, namely that of the Lagrangian Point L1.
And on balance, in this way even the strongest materials currently available,
carbon polymers such as Zylon could comfortably withstand the weight and stresses of a cable
descending from the Moon to geosynchronous orbit. The savings would be enormous. It would reduce the
fuel needed to reach the Moon's surface, and vice versa, to one-tenth of what it is today.
We're still in the realm of future visions, it's true... but right now, Shizuoka University
in Japan, the Obayashi Corporation and the China Academy of Launch Vehicle Technology
are trying to find a way to build a space elevator within a few decades.
About two years ago, engineers at Shizuoka University created a scale model of one using
two 10-cm satellites connected by a 10-meter-long steel cable. A small motorized container traveled
along the cable, while cameras at either end tracked its progress. Based on the data obtained,
scientists will determine whether the entire system can be safely replicated on a larger scale.
The Obayashi Corporation plans to build a space elevator by 2050.
This would involve building a 400-meter-diameter floating anchor platform on Earth,
connected by a carbon nanotube cable to a 12,500-ton counterweight in space.
In contrast, the China Academy of Launch Vehicle Technology plans to have a working
space elevator by 2045. Tsinghua University's research team has already developed a type of
carbon nanotube fiber that is believed to be the key to creating a super-strong cable. Chinese
scientists have also conducted space tethering experiments, but without releasing details.
It's true, all this may seem only a dream of the beginning of this millennium,
similar to the grandiose and far-fetched futuristic visions dreamt during the various
universal expositions of the early twentieth century... then revealed as naive illusions...
The fundamental difference is however in the economic benefit, that is in the incredible
savings that such a realization could guarantee to the space agencies. Space colonization is
in fact limited by the very high costs of the vectors necessary to bring in orbit the payloads.
And as we know, in a globalized system like ours, the real engine of everything, especially
with the recent entry into the competition by private companies, is the economic statement.
Obviously, there are great challenges to overcome, just like those who built the
first transcontinental railroad and the Panama and Suez canals, or those who in ten years took
us to the moon... It will take a lot of time and money, but it will eventually get done.
That is, unless something better and safer is found in the meantime.