An ion engine is a type of electric propulsion system used in spacecraft. It generates thrust by accelerating ions, which are charged particles, using electric fields. This method allows for a much higher efficiency compared to traditional chemical rockets, making it ideal for long-duration space missions. Ion engines operate by ionizing a propellant, often xenon, and then using magnetic or electric fields to propel the ions out of the engine. This creates a small but continuous thrust, enabling spacecraft to gradually build up speed over time. They have been used in missions like NASA's Dawn spacecraft, showcasing their effectiveness in deep space exploration.