Could You Use Electrons as Propulsion?

Electrons are a group of repulsive particles, not in the negative sense of being unpleasant, but in the charge sense. When electrons are side by side, they repel each other. However, a negatively charged electron is strongly attracted to a positive charge. This principle is utilized in old-fashioned TV picture tubes, which contain electron guns that emit electrons at high energies. Electron guns are simple devices consisting of a few pieces of metal and a filament cathode that emits electrons. Here’s the catch: as a spacecraft emits electrons, they move away at high speed. But charge is conserved, and the spacecraft becomes positively charged. The electrons that left feel this positive charge and slow down, stopping, and then accelerate back toward the spacecraft. Ultimately, no propulsion occurs from these electrons alone. We would need to neutralize the electrons with something, typically ions, which are atoms with an electron removed. Therefore, the standard technique is to accelerate ions, which are thousands of times more massive than electrons, and once these are streaming away, a matching number of electrons are squirted along to ensure the electric rocket exhaust remains charge neutral.

Spacecraft Electric Propulsion: A Detailed Overview

Electric propulsion is a type of spacecraft propulsion technique that uses electrostatic or electromagnetic fields to accelerate mass to high speed, thereby generating thrust to modify a spacecraft's velocity in orbit. The propulsion system is controlled by power electronics. Although electric thrusters use much less propellant than chemical rockets due to their higher exhaust speed and higher specific impulse, the thrust is significantly weaker compared to chemical rockets. However, electric propulsion can provide thrust for much longer periods.

Electric propulsion was first successfully demonstrated by NASA and is now a mature and widely used technology on spacecraft. American and Russian satellites have used electric propulsion for decades. As of 2019, over 500 spacecraft operated throughout the Solar System used electric propulsion for station keeping, orbit raising, or primary propulsion. Future advancements could enable advanced electric thrusters to impart a delta-v of 100 km/s (62 mi/s), sufficient for taking a spacecraft to the outer planets with nuclear power, but insufficient for interstellar travel. An electric rocket with an external power source transmissible through laser on the photovoltaic panels has a theoretical possibility for interstellar flight. However, electric propulsion is not suitable for launches from the Earth's surface as it offers too little thrust.

On a journey to Mars, an electrically powered ship might be able to carry 70% of its initial mass to the destination, whereas a chemical rocket could carry only a few percent. This makes electric propulsion an attractive option for missions that require extended durations and do not have the strict limitations of Earth launches.

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