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PLASMA MAGAZINE

Published in Issue Nr. 3
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Plasma Rockets

Plasma Rockets are the new renaissance in space travel. Like electric cars in space, they are the most efficient way to use both fuel and power to move a spacecraft. All rockets carry “propellant” that is pushed out in one direction, which results in a push, or “thrust”, on the spacecraft in the opposite direction (every action has an equal and opposite reaction…). Like conventional space rockets, it must carry all its propellant; but unlike conventional rockets, they use electric power to be super-efficient with this propellant. Since it is very expensive to carry propellant into space, the high propellant efficiency of plasma rockets is very attractive for many space missions, many of which are now only possible with plasma rockets.

This efficiency has not gone unnoticed. Plasma rockets, commonly called “Electric Propulsion”, are now being used on hundreds of spacecraft for the aerospace industry and space agencies in Europe, the United States, and Japan. Many of these spacecraft orbit the Earth where plasma rockets improve the mission life and capabilities. But plasma rockets really shine when it comes to space exploration, where their fuel efficiency allows relatively small spacecraft to do amazing exploration and sample return missions to the Moon and asteroids. For future space missions, plasma rockets are at the top of the list for missions to mine asteroids, travel to other planets in our solar system, search for Earth-like planets around other stars, and even take humans and supplies to and from Mars.

Why are Plasma Rockets so efficient? The goal of any good rocket is to push its propellant out at a very high speed. Most conventional “chemical” rockets do this by using a controlled explosion that is directed through a nozzle so that the propellant leaves the nozzle at supersonic speeds. This works well, but plasma rockets can accelerate their propellant to much higher speeds than chemical rockets. Therefore, most plasma rockets can get nearly ten times more thrust for every gram of propellant they use. The good news is that this means you only need a very small amount of propellant.

How do Plasma Rockets get their propellant to exit at extremely high speeds? The trick is to turn the propellant into electrically charged ions by removing electrons. There are many ways to do this, but the most common way is to bombard the propellant with high energy electrons, which liberates at least one of the electrons from the propellant atoms, thus creating a soup of charged ions and electrons. This soup is called “plasma.”  Now, you have the first part of a plasma rocket. The next step is to accelerate the ions (which are well over 10,000 times heavier than the electrons) to high speeds using high voltages. Most plasma rockets use voltages from about 300 V to 3000 V, which results in exhaust speeds over 10 times that of conventional chemical rockets.

The electric power used to “ionize” and “accelerate” the plasma comes from the solar power collected by the spacecraft. The solar power levels of a spacecraft are very small compared to the power levels of chemical rockets, so plasma rockets provide relatively small levels of thrust. This low thrust is great for moving spacecraft around in space at high efficiency, but is not the right choice for high thrust maneuvers such as launch, where chemical rockets shine.

With the recent growth in the use of high efficiency plasma rockets, we now have the perfect complement to conventional chemical rockets for space travel. Many new plasma rockets are being developed today for all sizes of spacecraft, from very large cargo carriers to very small “micro-satellites.” These plasma rockets will further allow us to expand our frontiers and understanding of Earth, our solar system, and the universe.

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