The space elevator is one of those concepts that gain legendary status long before it becomes a tangible reality. Were it to manifest itself, it would revolutionize space travel in ways that neither you nor I could ever have anticipated. Where do we build them though? Does it matter? What else should we know about space elevators?
The best place for a space elevator construction site is along the equator because it is the apex of the Earth’s curvature and the point at which the greatest centrifugal force can be generated from the planet’s rotation. At present, the best elevator construction mechanism known is the “tether-ball pole” model.
Elon Musk doesn’t believe the concept would work in the real world, let alone in the next few decades. What does he know though? We take a look at the theories and hypotheses underlying the space elevator.
What is the best place on Earth to build a space elevator?
We will need the space elevator to stand as straight as possible, of course. However, unlike your run-of-the-mill skyscraper, we will have to factor in the curvature of the Earth to find the best place to station the construction. We need to find a place where it is easiest to counteract gravity’s pull on the space elevator.
The equator is the ideal sweet spot we are looking for. This is because it is the apex of the Earth’s curvature, and the centrifugal force generated by the rotating Earth is most powerful here. When centrifugal force is applied at the top to pull the structure towards space, it will be held taut and perfectly balanced by the two counteracting forces.
Due to the space elevator’s great height, building on non-equatorial sites will leave the tower skewed over land surrounding the base. This skewness leaves the elevator subject to the gravitational pulls of this surrounding land. Besides, centrifugal force on the tether would be weaker if it was placed on a non-Equatorial site. This would seriously hinder balance, as well as lead to many docking and loading problems at orbit stations.
This perfect tautness is also required because the elevator shaft will have to resist potential impacts with satellites or space debris.
What would it take to build a space elevator?
It is at this question that we hit our first, and biggest, stumbling block. When it comes to space elevators, we have the science down pat…pretty much. What we do not have is the materials necessary to do the hyper-demanding job. No known material has been proven to be a suitable choice for building a space elevator.
The material (or materials) that can successfully carry out the task must be of high tensile strength to survive the constant tug of war between the upper centrifugal force and gravity. The materials must also have insulation properties, to shield users of the space elevator from the elements.
For humans, there is also the threat of exposure to radiation as we ascend towards the heavens. Zones of energetically charged particles known as Van Allen radiation belts can be created anywhere between 400 and 36,000 miles from the Earth’s surface. These are radiation “clouds” made up of charged particles that originate from the solar wind. They are held together to form belts by the Earth’s magnetic pull. Doubtless then, we will need a material that is strong enough to see off such radiation and keep elevator users safe.
At present, the top candidate, theoretically, comes in the form of carbon nanotubes (CNTs). These are clever networks of carbon-based tubes. The tubes can have variable lengths, but their diameters are measured in nanometers. The material’s chemical composition is highly modifiable, which means it can be prepared to suit a specific construction atmosphere.
Another added benefit is the extremely high tensile strength. Carbon nanotubes have covalent sp2 bonds, which are perfect if they are to be pulled apart. This is extremely lucky for us because this is exactly what the elevator shaft will experience. Remember the centrifugal/gravitational tug of war?
They are utterly useless under compression, ironically, which makes it impossible to use them for constructing everyday multilevel buildings and skyscrapers. Ultimately though, carbon nanotubes are not quite capable of handling the long-term load, but they are a good foothold as a concept. With more modification, re-enforcement, or even the emergence of a product inspired by this invention, we might yet see a nanotube space elevator.
Who is building a space elevator and where?
Many players are very interested in this idea of elevators that reach into the heavens but such a project can only be handled by the wealthiest individuals, organizations, or nations.
Japanese construction giant, Obayashi Corp., has unveiled plans to have the world’s first space elevator up and running by 2050 and even shared a concept video of it. The company works closely with several institutions, including Shizuoka University and Nihon University’s Aoki Laboratory, to devise mechanical plans, prototypes, test materials, and so forth. Obayashi has, in recent years, initiated the process of exploring the legal and national security issues that surround such new technology.
Obayashi Corp. has labeled its great space elevator project the STARS-Me (Space Tethered Autonomous Robotic Satellite- Mini elevator), and have enlisted Shizuoka University as a partner to help them research and design the ideal tether and climber system.
At the same time, the Science Council of Japan and the Department of Precision Machinery Engineering are also going full steam ahead with a hybrid space elevator construction approach. This involves the simultaneous construction of docking stations, both on the Earth’s surface and in geosynchronous orbit. The joining tether will be added later when the technology has sufficiently developed.
China also made a splash around this topic by announcing plans to have one ready by 2045, but no concept materials have been shared thus far.
Is it possible to build an elevator to the moon?
Incredibly, there is great hope within the space science community that lunar space elevators are not only possible but far more feasible than space elevators that originate from Earth. The main reason for such optimism is the moon’s relatively weaker gravity. The moon’s gravity makes it a better base for the elevator tether.
Astronomy graduate students Zephyr Penoyre and Emily Sandford came up with the concept of a lunar “Spaceline”. This system consists of a single 200,000-mile-long cable that would be anchored to the moon’s surface and stretch all the way into Earth’s orbit. Because the Earth and moon are constantly moving, it would not be possible to anchor the other end of the tether to the Earth’s surface. However, keeping the unanchored end of the tether within the planet’s orbit allows it to still experience the gravitational pull that will be needed to keep the tether taut.
Unfortunately, this method will not eliminate the need for rocket launches and their associated environmental problems. To be able to access the moon, people would first have to fly up to the untethered end of the space elevator. Once there, automated robotic vehicles attached to the tether can be loaded up and ferry people, and cargo, to the moon’s surface.
Is it possible to build an elevator to Mars?
At present, it is not possible to build a space elevator that stretches from Earth to Mars. For one, the sheer distance between the two planets makes such an undertaking impossible. Secondly, both planets move along their respective orbits at different paces, which makes the alignment of a space elevator between them impossible as well.
However, what IS possible, in theory at least, is the construction of a Martian space elevator spanning from Mars’ surface to its orbit. Mars has a relatively weaker gravitational pull than Earth, so the construction would be fairly easier because the less centrifugal force would be required to act against gravity.
Does a space elevator have to be on the equator?
In short, yes. Space elevators have to be on the equator if they are to follow the tether-ball model. As we touched on earlier, a space elevator on Earth needs to counteract the force of gravity acting upon it so it does not collapse upon itself.
Currently, the best way to do that for construction like this is to make use of centrifugal force generated by the planet’s axial rotation. The equator is the best place to site the tether because this is where the greatest centrifugal force can be generated. Sites that are not along the equator may result in towers that do not have enough centrifugal force to counteract gravity.
Choosing non-equatorial sites can also lead to other problems in the future. The docking of space elevator climbers at geosynchronous stations could be hindered by the awkward skewness that may be borne out of choosing non-equatorial sites.