Monday, December 31, 2012
Here's a helpful pdf showing the difference between two ion engines: NSTAR, currently being used on Dawn and before on a number of missions, and the newer NEXT, certified for use in 2008. This article from New Scientist probably does the best job explaining the difference between the two (and some other ion engines used by other space agencies), but the pdf also has a nice chart that does just as good a job:
For reference, the trajectory map for Dawn shows just how much time Dawn spends thrusting. Nevertheless, Dawn is continuing along its merry way and is now 2.7 million km away from Vesta and 56.8 million km away from Ceres, just 21 times the distance.