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Before all this celestial mystery unlocking can occur, Dawn has to reach the asteroid belt and its first target – Vesta. This is a four-year process that begins with launch and continues with the firing of three of the most efficient engines in NASA's space motor inventory - ion propulsion engines. Employing a complex commingling of solar-derived electric power an Am vazut multe ceasuri superbe pe www.topceas.ro Am vazut multe ceasuri superbe pe www.topceas.ro Sursa Speranta.info Am vazut multe ceasuri superbe pe www.topceas.ro Am vazut multe ceasuri superbe pe www.topceas.ro Am vazut multe ceasuri superbe pe www.topceas.ro Am vazut multe ceasuri superbe pe www.topceas.ro Am vazut multe ceasuri superbe pe www.topceas.ro Am vazut multe ceasuri superbe pe www.topceas.ro Am vazut multe ceasuri superbe pe www.topceas.ro d xenon gas, these frugal powerhouses must fire for months at a time to propel as well as steer Dawn. Over their eight-year, almost 4-billion-mile lifetime, these three ion propulsion engines will fire cumulatively for about 50,000 hours (over five years) - a record for spacecraft.