Looking up at the sky and questioning what lies beyond has always been something the human species has done. It is through this curiosity that the study of astrophysics began, enabling new discoveries and a continuous search of space.
Based on this, space exploration is growing constantly, using advanced technologies, launching satellites, and constructing rockets and spaceships. However, the vastness of the universe makes significant advances difficult, leading to the question of how we can explore space more quickly.
Therefore, concepts such as the space elevator, skyhook, and mass driver have emerged as potential ways for humans to travel through space at a faster pace. So, what exactly are these concepts and how do they work?
A space elevator is a proposed planet-to-space transportation system that relies on a cable, or tether, anchored to the Earth’s surface and extending into space. One end of the cable would be attached to the Earth near the equator, while the other end would be connected to a counterweight, such as a space station or platform, floating beyond geostationary orbit at an altitude of 35,786 km.
In theory, a space elevator offers a more cost-effective and energy-efficient means of reaching low Earth orbit compared to traditional rockets. Instead of expending energy to travel both upwards and sideways, as rockets do, a space elevator would only need to provide the energy to move upwards. This reduces the amount of fuel required and potentially makes space travel more environmentally friendly. Additionally, once the space elevator is constructed, it could significantly lower the cost of sending objects and even people to space. The velocity of the counterweight could be harnessed to launch spacecraft into space, acting as a platform located outside the Earth’s atmosphere.
However, there are several challenges associated with the concept. Building a space elevator would require a massive and sturdy base located near the equator to account for the Earth’s rotation. The cable or structure must be able to withstand various atmospheric challenges, such as radiation, corrosion, and debris collisions, while remaining lightweight and affordable. It needs to be built correctly on the first try because if the cable were to break at the top, it would likely fall to Earth, causing a disaster. Also, currently, no material has been identified that can fully meet these requirements, although carbon nanotubes have shown promise. Another significant challenge is the time it would take to ascend the elevator, estimated to be around 8 days, and the considerable amount of energy it would consume.
As of now, these problems remain unsolved, which makes the concept of a space elevator more of an idea present in films and games rather than a practical reality.
SKYHOOK: A more practical and viable solution
Another concept is the Skyhook, which differs from the space elevator in that it is a simpler technology that does not require new scientific breakthroughs or magical materials. It has already been tested in other structures and shows promise.
The Skyhook consists of a tether, essentially a cable, and a weight. It functions as a type of ladder to ascend and gain speed. A material called zylon fiber, which already exists, can serve as the cable due to its ability to withstand the tension involved, which is less compared to the elevator.
There have been missions like TSS-1R aimed at testing the engineering performance of the Tethered Satellite System, studying electromagnetic interaction, and investigating the forces at play. While TSS-1R, one of the initial missions, was not entirely successful, it provided valuable insights into the structure and helped identify potential solutions to the observed problems.
To operate, the Skyhook requires a hook attached at the bottom to capture a spaceship located at an altitude of 80-150 kilometers from Earth’s surface. The cable needs to be at least 1000 km in length. It is crucial for the system to maintain a constant spin, with the counterweight holding a cable that rotates around a circle. This mechanism reduces the relative speed at the bottom while increasing it at the top, transferring the energy from the hook to provide a boost for releasing the payload, similar to a catapult.
Although the Skyhook concept appears simple and promising, there are several challenges that need to be addressed. The bottom of the Skyhook reaches a velocity of approximately 12,000 km/h and passes over the same location on Earth multiple times a day. This means that it is not stationary, requiring a special spacecraft capable of matching its speed to catch the Skyhook. Alternatively, a method such as a fishing line with a drone attached to the structure could be developed to capture the spacecraft. Additionally, the Skyhook must continue spinning to avoid falling back to Earth. This necessitates maintaining a balance between departing and arriving spacecraft to sustain momentum or employing an engine to periodically correct its position.
If the Skyhook concept proves successful in Earth’s orbit, it could also be utilized on other planets, facilitating large-scale and efficient interplanetary communication. For instance, it could significantly reduce travel time to Mars from many months to only a few.
Also, because of the lower gravity in other planets and moons, the speed and size of the Skyhook can be smaller, making it easier to build and apply.
In the case of Mars, the two moons, Phobos and Deimos, could serve as ideal counterweights for the Skyhook system. Their significant mass would eliminate the need for constant position corrections, and their strategic positions within the solar system would enable swift transportation, and reduce even more travel time.
However, a question arises: If we can build this structure, how can we launch a spacecraft at high speeds to reach the Skyhook? One potential solution is the implementation of a mass driver.
A mass driver, also known as an electromagnetic catapult, is a proposed method for non-rocket space launch. It involves using a linear motor, typically consisting of coils of wire energized by electricity to create electromagnets, to accelerate and catapult payloads to high speeds. Sequential firing of these electromagnets propels the payload along a designated path, and once the payload leaves the path, it continues to move due to its momentum.
In the context of space launch, a mass driver essentially functions as a coilgun that magnetically accelerates a package containing a magnetizable holder and payload. Once the payload has been accelerated, the holder is separated and slowed down, ready to be reused for another payload.
It can potentially be designed as a long, horizontally aligned launch track for space launch, gradually bending upwards at the end, utilizing both track curvature and Earth’s own curvature to achieve the desired target velocity without subjecting passengers to excessive g-forces.
Implementing Earth-based mass drivers for propelling vehicles to orbit, such as the StarTram concept, would require significant capital investment and a new study of how to do so effectively. The Earth’s strong gravity and thick atmosphere pose challenges to the practical implementation of such a system. However, natural elevations like mountains may aid in the construction of the long track required for the mass driver. The higher the track terminates, the less atmospheric resistance the launched object will encounter.
Although implementing a combination of the Skyhook and a mass driver holds the potential to revolutionize interplanetary travel, making it faster, more cost-effective, and reducing the logistical challenges associated with long-duration space missions, it is important to note that the Skyhook, Mass Driver and also the space elevator concepts still require extensive research, development, and engineering to overcome technical hurdles and ensure their practical viability.
Author: Arthur Leite