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Dawn at Ceres

March 4, 2015

An asteroid-chasing spacecraft is about to make history. If all goes well, it’ll enter orbit around the largest asteroid this week. That will give it two notes in the history books: It’ll be the first spacecraft to study Ceres from close range, and it’ll be the first to orbit two bodies beyond Earth.

Dawn was launched seven-and-a-half years ago. It entered orbit around its first target, the asteroid Vesta, in July 2011, and stayed there for 14 months. It then fired up its engines again and headed toward Ceres.

Those engines are quite different from those on most spacecraft. Most missions use chemical rockets to get around, like those on the big boosters that blast them into space. Such engines produce a lot of power, but they’re heavy and they burn through a lot of fuel.

Dawn is powered by ion engines. They use an electric charge to fire out molecules of xenon. That produces only a tiny amount of thrust, but an engine can fire for days without stopping, so the “kick” adds up. And the engines need only a fraction as much fuel as standard rockets. In fact, without the ion engines, Dawn would have been much too big and heavy to even launch.

Although Dawn will enter orbit around Ceres this week, it’ll take several more weeks to reach the right orbit to conduct its scientific observations. After that, it’ll spend many months looking at Ceres — a world that may have an ocean of liquid water beneath its rocky crust. More about that tomorrow.

Script by Damond Benningfield, Copyright 2015

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