How to save fuel in space?
Space Elevators, Slingshot Effect and Rail guns explained...
Fuel conservation is as important as fuel production - Veerappa Moily
Greetings, fellow Bohron
Until now we have explored the following three means of transport to carry us to the stars: Ion/Plasma Engine, Solar Sail, and Ramjet Fusion Engine. Although the last one comes closest to fulfilling our needs, none of these provides a complete solution to our problem.
Currently, fuel prices are at their all-time high. Everybody’s concerned about the efficiency of their vehicles. The aerospace industry faces the same problem today. Luckily, we have some methods at our disposal to reduce fuel costs, at least in space. Let’s explore them now.
Space Elevators
All the designs we have discussed suffer from an almost insurmountable hurdle: the development of humongous space vehicles on Earth. The parts of such machines are so heavy that a lot of money is spent on lifting them against the Earth’s gravity and putting them in their place and eventually driving the rocket off the gravitational field. For example, the ISS costs 150 billion USD.
The solution is to build them in space. To achieve this, scientists have now busied themselves in the development of what they call Space Elevators. Since in space the effect of gravity is minimal, even the heaviest of objects (on Earth) can be lifted with utmost ease.
Russian rocket scientist Konstantin Tsiolkovsky first theorised space elevators in 1895. Inspired by Eiffel Tower, he envisioned a huge tower ascending into the heavens to the height of geostationary orbits. His design required the tower to be constructed of very high-strength material to support its weight, unavailable at his time.
A better proposal was put forward by Russian engineer Yuri N. Artsutanov in his article, “To the Cosmos by Electric Train” published in 1960. He followed a top-down approach: a geostationary satellite in orbit would be the base for the tower, and then a cable would be dropped from the tower using a counterweight which would be linked to Earth’s surface. This design had its own problems: withstanding extremely high tension wasn’t possible for any material developed till then.
The development of carbon nanotubes has revived the interest of engineers in space elevators.
Carbon NanoTubes (CNTs) are extremely small hexagonal lattices of carbon with the strongest known tensile strength of all materials. CNTs are lightweight, strong and have useful optical properties
Currently, it costs $2,720 per kilogram to carry into space for a SpaceX Falcon 9 rocket. If a space elevator is developed, the expenditure on space travel would reduce profoundly. In the far future, it might become possible to visit outer space at the price of a plane ticket.
There are some considerable hurdles we’ll have to cross to realize a space elevator:
It is very difficult to grow CNTs in bulk. In 2020, researchers at Waseda University, Japan, grew bunches of nanotubes up to 14 cm long. Building a space elevator would require CNTs that are thousands of miles long.
The presence of microscopic impurities or misalignment of even a single atom in the tube greatly reduces the strength of the material.
Given the large number of artificial satellites that are in orbit around the Earth, some of them might collide with the elevator. Collisions with micrometeorites are even more probable.
Slingshot Manoeuvre
Sometimes when a probe is sent to outer space, it goes around a nearby planet and uses its gravity to gain acceleration and send itself flying into the intended direction, hence saving fuel. This technique is known as gravity assist or slingshot manoeuvre and is possible because of Newton’s Third Law.
A spacecraft using the slingshot effect gains its energy from the motion of a planet or star. In August 2017, researchers discovered two neutron stars that are revolving around each other at great speed. Physicist Freeman Dyson proposed that by travelling extremely close to one of these neutron stars, we could whip around it and then be hurled into space at speeds approaching a third the speed of light.
Rail Gun
Conventional rockets use fuel or gunpowder to boost a projectile to high velocity. A rail gun, however, uses the power of electromagnetism. The basic design of a rail gun consists of two parallel wires or rails, with a projectile that straddles both wires, forming a U-shaped configuration.
When a wire-carrying current is placed in a magnetic field, it experiences an electromagnetic force. A current-carrying wire itself produces a magnetic field around it. This is because charges are in motion inside the wire. When high currents (e.g., of order one million amperes) are sent in the wires, a magnetic field of enormous strength is generated which moves the projectile up or down the rails.
A major problem with the rail gun is durability. It accelerates payloads so fast that they often deform upon impact with the air. So the bones of an astronaut under the influence of such strong g-forces would be crushed leading to death.
Tests using rail gun technology have been successfully conducted by USA’s DARPA and India’s DRDO. China is developing its own railgun system. It has already begun testing its electromagnetic rail gun at sea.
Sources:
Ch 9: Starships, Physics of the Impossible - Michio Kaku
Space elevator -Wikipedia
New method smashes record for longest carbon nanotube forests ever made. Michael Irving, November 04, 2020 - New Atlas
Railgun - Wikipedia