After more than seven years of travelling across the solar system, NASA’s Dawn spacecraft has finally reached the last part of its mission which involves orbiting the dwarf planet Ceres and sending back images and data. Perhaps the most interesting thing about Dawn, however, is that rather than moving using traditional rockets, the spacecraft uses an electrically-powered ion engine. It is this kind of engine that the next generation of spacecraft will use.
The NASA spacecraft Dawn has spent more than seven years traveling across the solar system to intercept the asteroid Vesta and the dwarf planet Ceres. Now in orbit around Ceres, the probe has returned the first images and data from these distant objects. But inside Dawn itself is another first—the spacecraft is the first exploratory space mission to use an electrically-powered ion engine rather than conventional rockets. The ion engine will propel the next generation of spacecraft. Electric power is used to create charged particles of the fuel, usually the gas xenon, and accelerate them to extremely high velocities. The exhaust velocity of conventional rockets is limited by the chemical energy stored in the fuel’s molecular bonds, which limits the thrust to about 5 km/s. Ion engines are in principle limited only by the electrical power available on the spacecraft, but typically the exhaust speed of the charged particles range from 15 km/s to 35 km/s.