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“Warp speed Mr. Sulu, take us home”, Captain James T. Kirk orders from the bridge the starship Enterprise in the science fiction television series Star Trek. Kirk and the crew of the Enterprise made traveling around the universe seem easy in the future. But that was science fiction, not science fact, right?
Not so fast. It turns out that one of NASA’s current missions was inspired in part by Captain Kirk. The cutting-edge Dawn mission will explore two huge asteroids named Ceres and Vesta. It is powered by an innovative ion propulsion engine. This is technology that Dawn Mission chief engineer Marc Rayman, first heard about years ago, while watching, you guessed it, Star Trek.
All of us learn about ions in first-year chemistry as we study atoms and molecules. An ion is just a charged atom. The charge occurs when the atom gains or loses electrons. This helps us explain how atoms combine together to make compounds, but how does it help send a spacecraft into deep space?
Typical rocket engines work when fuel is burned in a chemical reaction that rapidly produces large volumes of hot gases that exit through nozzles in the rear of the engine. But this takes a lot of fuel, too much to power the Dawn Mission. Adding enough fuel would make it too heavy to launch.
Ion engines take a different approach. Energy from a huge solar array is used to strip electrons from xenon atoms giving them a positive charge. The xenon ions pass between charged metal plates and are expelled out of the back of the spacecraft, which pushes it forward. This doesn’t exactly make it a hot rod—it would take four days to go from 0 miles per hour to 60 miles per hour.
Conventional rocket engines thrust for a few minutes at most, before they run out of fuel. Then they must just coast to their destination. The ion propulsion engine in Dawn is so efficient it will thrust off and on for five years, gradually adding velocity.
This innovative propulsion system has allowed the Dawn spacecraft to enter orbit around not just one, but two different asteroids. It is currently in orbit around Vesta and will soon depart for orbit around asteroid Ceres, going, like the starship Enterprise, “where no man has gone before”!