Tower of Babel to space! See how it works!
Over the past century, humans have done some pretty amazing things. After the White brothers invented their first airplane in 1903, it took us only 66 years to send people to the moon. Our engineering and scientific prowess is obviously impressive, but maybe it's time for us to take a look at some of the challenges, some beyond anyone's imagination... Maybe it's finally time to build a space elevator.
What is a space elevator?
The concept of a space elevator was first proposed in 1895 by Konstantin Tsiolovsky, who proposed the famous "Rocket Equation" to help send rockets into space (his contribution to the cause of space was enormous). Tsiolkovsky's concept of a space elevator was inspired by the Eiffel Tower, which was built almost at the same time. He wondered if humans could build a tower high enough to have its tip extend into space so that we could simply climb the elevator, climb this ridiculously tall building, and cross the gravitational barrier to reach the stars instead of firing rockets to get there.
Currently, the tallest building in the world is dubai's Burj Khalifa, which stands at 829.8 meters (2722 feet). It holds the record for the tallest building ever built by man, surpassing the previous record of 646.38 m (2120.7 ft) for the Warsaw Broadcasting Mast, which actually collapsed during construction. A viable space elevator would have to be at least 35,786 kilometers (22,236 miles) high — the altitude at which the object reached geostationary orbit. In contrast, if the height of the Burj Khalifa is equivalent to the height of a coffee cup (8.25 cm), the height of the space elevator will be 3.56 km, which is more than 4.3 times the height of the actual Burj Khalifa!
The geostationary orbit refers to the altitude at the equator from the Earth's surface, and the time it takes an object to complete an orbit is the same as the Earth's rotation period, that is, one day. This essentially means that if you're on a spaceship directly above a point on Earth (say Pontianak in Indonesia, which is directly on the equator), you'll never move relative to that point. So if you look down, the city will always remain directly below you, and if you stay on track, the city will never move relative to you.
What materials will the space elevator be made of?
Remember, 36,000 kilometers (to reach geostationary orbit) is the minimum altitude we need to reach for the space elevator to work properly. However, the centroid needs to be at an altitude in geostationary orbit; anything below this altitude makes the system unstable. Ideally, the space elevator is about 100,000 kilometers (62,000 miles) high. Come to think of it, the coverage distance we are talking about is almost a third of the distance to the moon! At such a distance, we will have to start building most of the elevators in space, as well as several large spaceships and thousands of people building this tower in zero gravity.
Another approach is to launch a giant ribbon scroll into geostationary orbit and then fall toward Earth, while releasing another scroll upwards to counteract gravity and stay in orbit. The original spacecraft would remain in geostationary orbit and have long cables extending in both directions. The idea looks like it came straight out of science fiction; the engineering and materials technology required for such an idea is far more advanced than we can currently do.
The space elevator requires extremely high tensile strength to counteract the gravity that pulls the 100,000-kilometer megastructure down, as well as the centrifugal force and inertia of the counterweight that pulls it upwards (we'll cover this later). It needs to remain stable and functional in extreme heat and cold, unpredictable forces from the atmosphere, and radiation from outer space. Most importantly, it must survive the particles of miniature meteorites and the solar wind constantly hitting it. Does a substance that can tick all these requirements really exist? We think carbon nanotubes may be the answer.
Carbon nanotubes are cylindrical carbon structures at the nanometer level; we can't find them in nature, and they're hard to make. They are the hardest and strongest substances ever discovered, and they exhibit very high tensile strength, making them exactly the kind of materials we need for space elevators. They are also conductive, so we don't need to lay extra wires to power climbers or elevators.
However, even with enormous strength, carbon nanotube cables can only support their own weight of about 5,000 to 7,000 kilometers before they are broken — far less than the 100,000 kilometers required for space elevators. That is, advances in technology allow us to reach the stage of producing suitable materials or manipulating existing ones.
Space lifts also require a counterweight to be added to the top. In other words, the elevator must be attached to something very heavy, just as it attaches to the ground at the bottom. The higher the elevator you build, the lighter this counterweight needs to be, so as to offset the extra mass you add to the cable itself. Equilibrium forces are necessary to ensure that the masses above and below the geostationary orbit are approximately the same; therefore, the centrifugal force pulling the system upwards is equal to the gravitational force of the downward pulling system.
If we build a space elevator with a minimum height of 35,786 km, the balance of weight will be enormous... Equivalent to one-third the size of the moon. One way to do this is to capture an asteroid and take it into orbit around it so we can build an elevator to it. If the great engineers of mankind had been 65 million years ago, perhaps the asteroids that wiped out the dinosaurs might have been used to build space elevators...
If your elevator is more than 50,000 kilometers high, the top of the elevator will travel on Earth at such a high speed that it will reach a so-called escape velocity — beyond which you will fly out of Earth's orbit. At this point, you can simply jump out of the elevator to reach the moon, although your orbit calculations have to be impressively precise to avoid floating in nothingness. The elevator extends to 100,00 kilometers, and if the stars (or planets) align, you'll have enough speed to plan a trip to Jupiter.
If it's really that hard, why build a space elevator?
All of these problems seem to have had little effect. Given the limitations of matter, science and economy, building a space elevator seems almost impossible. Furthermore, is there a need for this? We've been able to send things into space, and the ISS is inhabited (although they're in low-Earth orbit for about 450 kilometers, not 100,000 kilometers). The answer is cost. Currently, it costs about $10,000 to send a pound (0.45 kilogram) payload into orbit around Earth; interstellar travel costs much more. After building the space elevator, it costs about $90 to send the same payload, a 99 percent reduction in cost.
Building a space elevator would be humanity's most ambitious plan to date. This makes the White brothers' achievements insignificant in comparison, although not inferior in significance. Humans always seem to find a way to surpass themselves through their engineering capabilities. We're always looking for the next hurdle to overcome, the next challenge to overcome. Perhaps the technology and manpower required to build a space elevator is something we would never have dreamed of today, but let's not forget that 150 years ago, flying was still a distant dream for human beings. From this point of view, it is really difficult to say how close we are to building a 100,000-kilometer space elevator!
BY: sciabc
FY: Luo Dao
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