## Electric Propulsion

If you rub a balloon against a wool sweater, you will cause atoms on the surface of the balloon to exchange electrons with atoms in the sweater. These atoms then become ions, or atoms with either too many or too few electrons. You can tell that the balloon has been charged with ions (or static electricity) because its negatively charged atoms will be attracted to the positively charged atoms of your body. The balloon will stick to you.

Ion engines work in a similar way. Instead of having ions that are simply attracted to one another, ion engines pull ions past plates with opposite charges and out the back of the engine. The ejection of the ions creates thrust, just as the ejection of gases in a regular rocket engine does.

The ion engine consists of an ionization device called a cathode. The cathode sends electrons into the propellant. The electrons hit the propellant atoms and remove one or more of their electrons. These atoms have become positive ions. A positively charged plate in the front of the engine pushes these atoms forward. A negatively charged grid in the back of the engine pulls these ions out at great speeds. Just outside the last plate is another cathode that neutralizes the ion beam. Otherwise, it would be attracted right back toward the rocket.

 electrons impact beam of propellant atoms +grid - grid ions ejected to create ions x \ / at high speed propellant ■■'■.■.'A"-A; AvA'/A'.Av.V.AV.A*.'A*.'' * A-.'AvAvAv-V.'Ai ■.■■ ■ is ■ -/A vA vA'/V. A-. A'.* - I-.V ■ "■■*.■*.'.• V/A'A electrons emitted by cathode \ v-AvAv-V.-V.Av. m •••-AvAv-V.-V.A electrons injected into exhaust to neutralize ions

In an ion motor, a beam of ionized particles replaces the hot gases of a conventional rocket motor.

In an ion motor, a beam of ionized particles replaces the hot gases of a conventional rocket motor.