Wear on the grids over time limits the life of these thrusters. Electrostatic Thrusters A schematic of an gridded electrostatic ion thruster. The vast majority of ion thrusters rely on gaseous propellants, however. Xenon, krypton, or argon are common choices for these thrusters, though other materials, like magnesium, zinc, and iodine have been experimented with in some designs. A neutral gas is used as fuel, which is ionized by stripping electrons from the atoms, resulting in a supply of positive ions that can readily be accelerated by electrostatic or electromagnetic means to generate thrust. Ion thrusters come in a variety of forms, but the basic principle is a simple one: electricity is used to accelerate ions to a high velocity, forcing them out of the thruster, thus resulting in a reaction force which propels the spacecraft itself. This has flow on effects, where launch vehicles carrying that fuel to the space station need less fuel themselves to boost it into orbit, improving efficiency across the board. In an application regarding orbit-keeping for the ISS, one calculation suggested an ion thruster could reduce the space station’s annual fuel use from 7,500 kg to just 300 kg. It means that an ion thruster can achieve a given change in velocity for a space craft with far less fuel – an order of magnitude less, in some regards.
This better fuel efficiency has real implications for space travel. Electrostatic ion thrusters are almost an order of magnitude better, on the order of 2,000-3,000 seconds, with some reaching closer to 10,000 seconds in experiments, while the experimental VASIMR electromagnetic ion thruster predicts a specific impulse up to 12,000 seconds. It’s a little confusing to wrap your head around, but for the newly initiated, just keep in mind that higher numbers of specific impulse stand for greater fuel efficiency.įor comparison’s sake, the Space Shuttle’s Solid Rocket Boosters get a specific impulse of just 250 seconds, while liquid oxygen-liquid hydrogen rocket engines may reach closer to 450 seconds. Specific impulse, where we look at impulse per weight of propellant, is thus measured in Newton-seconds divided by Newtons, or simply seconds. Impulse is the integral of force over time, measured in Newton-seconds. The higher the specific impulse of a rocket thruster, the more thrust it generates per mass of fuel. Specific impulse measures how effectively a rocket engine creates thrust from the mass it throws out the back, whether by chemical or any other means. Credit: NASA, public domainīefore we dive into the world of ion thrusters, it’s important to understand the concept of specific impulse and fuel efficiency for rocket thrusters of all kinds. Ion engines won’t get you out of Earth’s gravity well, nor do they work in the atmosphere, but become useful when you’re in the vacuum of space. It’s All About Specific Impulse Chemical rocket engines provide huge thrust but are thirsty when it comes to fuel.
Let’s take a look at how ion thrusters work, and some of their interesting applications in the world of spacecraft! This manner of operation means that an ion thruster and a small mass of fuel can theoretically create a much larger delta-V than chemical rockets, perfect for long-range space missions to Mars and other applications, too. However, when applied over a great deal of time in the vacuum of space, it can lead to a huge change in velocity, or delta V. This tiny push won’t get you off the ground on Earth. Ion thrusters, in their various forms, offer an alternative solution – miniscule thrust, but high fuel efficiency.
Getting that fuel into orbit is costly, too! These rockets offer high thrust, but they are relatively fuel inefficient and thus, if you want a large change in velocity, you need to carry a lot of heavy fuel.
Spacecraft rocket engines come in a variety of forms and use a variety of fuels, but most rely on chemical reactions to blast propellants out of a nozzle, with the reaction force driving the spacecraft in the opposite direction.
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