NASA'S DAWN SPACE PROBE, which is propelled by an electric rocket called an ion thruster, nears the asteroid Vesta in this artist's conception. Vesta is its initial survey target; the asteroid Ceres, its second destination, floats in the far distance in the image (bright spot at upper right). A conventional chemical rocket engine would be able to carry enough fuel to reach only one of these asteroids. Image: Pat Rawlings SAIC
- Conventional rockets generate thrust by burning chemical fuel. Electric rockets propel space vehicles by applying electric or electromagnetic fields to clouds of charged particles, or plasmas, to accelerate them.
- Although electric rockets offer much lower thrust levels than their chemical cousins, they can eventually enable spacecraft to reach greater speeds for the same amount of propellant.
- Electric rockets’ high-speed capabilities and their efficient use of propellant make them valuable for deep-space missions.
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Alone amid the cosmic blackness, NASA's Dawn space probe speeds beyond the orbit of Mars toward the asteroid belt. Launched to search for insights into the birth of the solar system, the robotic spacecraft is on its way to study the asteroids Vesta and Ceres, two of the largest remnants of the planetary embryos that collided and combined some 4.57 billion years ago to form today's planets.
But the goals of the mission are not all that make this flight notable. Dawn, which took off in September 2007, is powered by a kind of space propulsion technology that is starting to take center stage for long-distance missions a plasma rocket engine. Such engines, now being developed in several advanced forms, generate thrust by electrically producing and manipulating ionized gas propellants rather than by burning liquid or solid chemical fuels, as conventional rockets do.