Thursday, May 06, 2010
A week ago Dawn's team had another informative update, explaining not just where Dawn is now but also how using an ion drive to enter the orbit of an object differs from the standard approach using a regular chemical rocket. This gradual approach where the probe achieves an orbit around the Sun nearly identical to that of Vesta before its slight pull is enough to bring it into orbit is why the probe's trajectory looks the way it does:
Something like New Horizons on the other hand has a much more direct trajectory:
The update mentions that the approach phase to Vesta will begin about three months before arrival, and given the slow approach one would think that there should be some interesting imagery of the asteroid some time before orbital insertion happens, but the update doesn't mention whether this will happen or not.
In the meantime, Dawn is also almost at the point where its distance from Vesta and Mars are the same, thus becoming the first spacecraft to be closer to Vesta than any other body in the Solar System. Last month the distance was:
0.3193 AU away from Mars, 0.597 AU from Vesta
Now it's 0.4037 AU from Mars, 0.4829 AU from Vesta.