* Astronomy

The Dawn spacecraft continues on course and on schedule for its bold campaign to unexplored worlds. The probe is thrusting gently with its ion propulsion system, as it has been for most of its time in space, gradually modifying its path around the Sun.

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Dawn continues its flight through the solar system with all systems functioning well. It is vitally important that the spacecraft is reliably staying on course and on schedule, gently and steadily thrusting with the bluish glow of its ion propulsion system; yet that doesn't lend itself to the sorts of spine-tingling, heart-pounding, hair-raising, planet-shattering logs for which Dawn is famous (at least among immigrants from brown dwarf systems reading these reports in the vicinities of active galactic nuclei). So let's turn out attention to consider a particular aspect of flying a mission with ion propulsion.
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NASA's Dawn Spacecraft Begins Interplanetary Cruise Phase Jet Propulsion Laboratory December 18, 2007

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NASA's Dawn spacecraft successfully completed the first test of its ion propulsion system over the weekend. The system is vital to the success of Dawn's 8-year, 1.6 billion-kilometre journey to asteroid Vesta and dwarf planet Ceres.

"Dawn is our baby and over the weekend it took some of its first steps. We have two months more checkout and characterization remaining before Dawn is considered mission operational, but this is a great start" - Dawn project manager Keyur Patel of NASA's Jet Propulsion Laboratory in Pasadena, California, US.

Members of the Dawn mission control team have been sending up commands and checking out spacecraft systems ever since its successful launch on Sept. 27. The first test firing of one of Dawn's three ion engines was the culmination of several days of careful preparation.
On Sunday, Oct. 7 at 02:07 GMT (Oct. 6 , 9:07 p.m. Eastern Daylight Time), the ion propulsion system began thrusting. Over the next 27 hours, spacecraft controllers and navigators at JPL monitored the engine's performance as it was put through its paces.

"We evaluated the engine's capabilities at five different throttle levels. From flight idle through full throttle, the engine performed flawlessly" - Jon Brophy, the Dawn project's ion propulsion manager at JPL.

Dawn's ion engines are extremely frugal powerhouses. The 27 hours of thrusting from the ion engine resulted in the consumption of less than .28 kilograms of the spacecraft's xenon fuel supply -- less than the contents of a can of soda. Dawn's fuel tank carries 425 kilograms of xenon propellant. Over their lifetime, Dawn's three ion propulsion engines will fire cumulatively for about 50,000 hours (over five years) -- a record for spacecraft.
Dawn will begin its exploration of asteroid Vesta in 2011 and the dwarf planet Ceres in 2015. These two icons of the asteroid belt have been witness to so much of our solar system's history. By utilizing the same set of instruments at two separate destinations, scientists can more accurately formulate comparisons and contrasts. Dawn's science instrument suite will measure shape, surface topography, tectonic history, elemental and mineral composition, and will seek out water-bearing minerals. In addition, the Dawn spacecraft itself and how it orbits both Vesta and Ceres will be used to measure the celestial bodies' masses and gravity fields.

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