“Popular Mechanics” №3, 2018
As soon as man realized that he could leave the earth with the help of rockets, he began to look for ways to do without them. From fantastic works, these ideas moved to the drawing boards of designers.
Alternative astronautics has developed in two ways: the creation of non-rocket or non-reactive means of reaching low Earth orbit and the creation of aids that make it easier for a rocket to reach space. The former include giant cannons, nuclear explosives, an orbital elevator, a “hyperloop”; to the second – aircraft and balloon launches, a nuclear hypersonic “gurkolet”, electromagnetic and railway boosters, etc.
From a gun to the moon
Before the advent of liquid propellant rocket engines, artillery was considered the only means of space travel. In Isaac Newton’s seminal work, The Mathematical Principles of Natural Philosophy, the concept of cosmic velocities was explained using a cannon that shoots farther and farther. Although it was already clear by then that even if a giant cannon could be built, launch overloads would kill any crew. In Jules Verne’s fantasy works, this problem was solved, but in the real world there is no solution to it to this day.
However, the weapon is only suitable for sending interplanetary or interstellar probes, the speed of which will exceed the second or third space speed. To launch near-Earth satellites at the first cosmic speed, a rocket stage will be required, because the trajectory of the projectile will pass through the launch point and it will inevitably crash into the Earth. This can be avoided by correcting the orbit on the cosmic segment of the trajectory, that is, the cannon can only be considered an auxiliary tool, and it will not be possible to do without rockets at all.
An attempt to implement Jules Verne’s ideas was made in the 1940s in the Third Reich: a giant cannon created under the V-3 program, dug to a depth of one hundred meters, was designed to bombard London from France. The shell was intended to cover 150 km, but the construction site on the English Channel was destroyed by British aircraft.
At the beginning of the space age, 1961-1967, cannon experiments continued in the United States. During the high-altitude research project (High Altitude Research Project, HARP) several guns of different calibers were created, which shot upwards to a height of 180 km. However, due to the apparent success of astronautics and the impossibility of making space launches using weapons, the project was curtailed.
An attempt to get ballistic missiles out of artillery was made in Iraq in the 1980s. The project was led by the American engineer Gerald Bull, who previously led work on HARP. A 1 m caliber gun was supposed to launch a 600-kilogram projectile at 1000 km. However, it did not come to practice: Bull was killed. The unfinished system was destroyed by US troops during Operation Desert Storm.
In the 1990s, experiments with weapons continued in the United States, allowing them to reach almost cosmic speeds. The SHARP (Super HARP) project at the Lawrence Laboratory in California conducted experiments with a gun on light gases, which gave a 5-kilogram projectile a speed of 3 km/s. Guns on light gases – hydrogen or helium – work according to the principle of pneumatic, only it is not air that is compressed before firing, but a low-density gas. Such cannons, which give the projectile a speed of up to 6-7 km/s, are used to simulate collisions with meteorites or space debris. The result of the experiments was the project of a gun that could accelerate the projectile to 11 km / s, but the billions of dollars required for the implementation of this idea were not allocated.
There are also physical limitations: for example, the projectile must gain space velocity only during its movement in the barrel. This speed must be higher than orbital to compensate for atmospheric drag. At a speed of several kilometers per second, the outer surface of the projectile heats up due to air friction and the formation of a shock wave. That is, the projectile must withstand not only colossal dynamic loads, but also temperature. However, they have already learned how to cope with aerodynamic heating during the launch of ballistic missiles and spacecraft, but it is not yet possible to bypass overloads.
Theoretically, the orbital launch artillery system is best placed at sea, in the form of a submersible barrel, as it could be moved and aimed at any point in the sky without being tied to a land-based gun carriage. On the other hand, building in the mountains would help remove some of the inhibiting effect of the atmosphere. A space gun could launch some simple cargo into orbit on an industrial scale, such as building materials or raw materials for production, but so far there is no need for such launches even in the long term, therefore no one builds weapons.
The electromagnetic gun is considered a possible way to fire in an airless environment – from orbital stations or the moon. Overloads cannot be avoided there either, but they will be lower.
The concept of a space elevator in the form of a thin tower hanging in the sky due to centrifugal force was described by Konstantin Tsiolkovsky in his essay “Dreams of the Earth and the Sky and the Effects of Universal Gravity” in 1895. The Soviet engineer Yuri Artsutanov developed this idea in 1960 by propose lowering a cable from a space station to Earth. The station will rotate in the plane of the equator in a geostationary orbit at an altitude of about 36,000 km. Even further away from Earth, a counterweight must rotate, which will balance the entire system due to centrifugal force. In the role of counterweight, one could use an asteroid or an even more massive station, which would be suitable for launching interplanetary vehicles and ships.
So far, the main technical obstacle to the implementation of this idea is the lack of a sufficiently strong low-density material from which a cable can be made. The cable must carry its own weight, geostationary station and counterweight. In addition, the tether must also withstand dynamic loads associated with cargo motion, orbital correction, Coriolis force, sunlight pressure, and gravitational influence from the moon, sun, and planets. Theoretically, carbon nanotubes should have the required strength, although the technology to produce tubes of sufficient quality and length has not yet been created.
The next task, to bring the implementation of the space elevator closer, is the development of the elevator. Since a space elevator does not include a system of multiple cables and cables, as in a conventional elevator, the space requires a cabin that can independently climb the cable. The energy for lifting is supposed to be transferred along the cable itself or with the help of a laser beam. Such a lift can be made now and since 2006 design competitions have been held in various countries. In 2006-2010, such competitions were held in the United States with the participation of NASA, but then they lost interest due to the lack of progress in creating a space tether. Competitors have designed devices capable of climbing at speeds up to 5 m/s. Then the ideas of a space elevator were taken up in Japan, Germany and Israel, where they also concentrated on a robotic elevator. Japanese construction company Obayashiwhich specializes in the construction of buildings, bridges and tunnels, plans to develop a space elevator by 2050.
However, creating a cable and a lift is half the battle. There are still many problems. For example, a taut cable stretched through outer space is too vulnerable a target for space debris. Now more than half a million fragments of debris larger than 1 cm are flying in near-Earth space at speeds up to 8 km/s. A collision at this speed with even a small metal fragment is equivalent to being hit by an armor-piercing projectile. Calculations show that, while maintaining the current density of space debris, the probability of a centimeter fragment of space debris colliding with a 5 cm wide tether is about 1/1000 per day, that is, once every three years. The danger of a terrorist act is not excluded: drones have appeared in the terrorist arsenal.
Don’t forget cosmic rays. The effect of the Van Allen radiation belts at altitudes from 1,000 to 17,000 km is strongest precisely in the plane of the equator, where the lift must rise. To overcome the lower, most dangerous proton belt at a speed of 100 m/s will take 17 hours. By comparison, ships Apollowhich flew to the Moon, skipped over it in less than 10 minutes at a speed of 10–11 km/s and tried to stay away from the equatorial plane, near the epicenter of the radiation belt.
Ultimately, the biggest problem with the space elevator is its economic feasibility. So far, humanity simply does not need such an intensive exchange of goods with space, which would make the capital construction of an elevator cost-effective – with high risks, huge maintenance costs and an incomprehensible view. Perhaps hope will appear at the beginning of active mining on asteroids or the moon, but until humanity needs these resources, it is the same on Earth.
The disadvantages of the space gun and the space elevator lack the design proposed by engineer Keith Lofstrom in 1981. This idea involves the use of only existing and mastered technologies, especially electromagnetic levitation (maglev), but it requires constant maintenance of a dynamic structure in motion to maintain its shape .
The basis of the launch loop is a looped metal cable, stretched between two stations on Earth at a distance of 2 thousand km. The cable is suspended between ring magnets inside the tube and twisted between the stations. Due to the moment of inertia of the rotating cable, the entire structure must rise into the air to a height of 80 km. Steering conductors should form part of an arc parallel to the ground. Thus, a gigantic arc will be obtained, which will make it possible to lift loads above the surface of the Earth into near space and set them to accelerate along guides, also based on the principle of maglev.
Despite the seemingly accessible technology, this project is even less real than a space gun or an elevator. The problem is not even in the initial investment – according to the developer, $10 billion should be enough, but in the costs of maintaining the structure in working order. Such a system requires an endless flow of cargo in outer space and high reliability, which does not allow even a second of downtime.
Many projects for alternative ways to reach space have been proposed. But they all lose to rockets because of their complexity and the lack of a real need for them. Humanity does not yet need a constant flow of hundreds of tons to and from space, and the rockets have not yet exhausted the resource with cost reduction.