MadSci Network: Physics |
By the nature of the ion rocket engine, it cannot produce a large force. You can (almost) place all rocket (and jet) engines into two simple categories: those which accelerate a lot of material a little AND those which accelerate a little material very much. The ion engine falls into this later category, as do many electric propulsion concepts. The ion engine only accelerates a very small amount of material and currently, such engines only produce thrusts around one hunredths of newtons (that's about 4 hundredths of an ounce of a push). Some produce more thrust, some less. You may be interested in reading about some other electric propulsion concepts, like the arcjet, the pulsed-plasma thruster, nuclear-electric propulsion (very different from nuclear propulsion!), the plane diode, and Hall-effect thrusters. I'm sure that there are more ideas than I know about. One thing that most have in common is the low-thrust characteristic. They just can't push hard. The benefit, as I'm sure you've read, is in the fuel consumption. These engines are much more fuel-efficient (and much weaker) than traditional chemical rockets. It sounds like you've read a lot on this already, but you may not be aware that this already has commercial use in Hughes Space & Communications XIPS See also, NASA: Ion propulsion You may have noticed that I haven't outright said "NO, you can't move a car with an ion engine" because, traditionally, those who claim something can't be done turn out to be wrong. However, as it stands, ion engines are only for space travel, where the lack of friction allows a little push to go a long way. [Moderator note: Ion engines are thrifty with mass but are not energy efficient. This is just fine for spacecraft because the reaction mass is limited and energy can be obtained from solar cells or nuclear thermoelectric generators. The ions travel at a very high speed which means that they have a high kinetic energy. For a given amount of thrust an ion engine might have ten times as much energy in its exhaust compared to the exhaust from a chemical rocket. Here on Earth we have plenty of "reaction mass", usually the Earth itself, and the problem is a lack of energy, so we have exactly opposite conditions to those where the ion engines do well.]
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