Dawn approaches Vesta, Approach phase, 3 May to 16 July 2011 Options

[Holder of the Tw...]

Latest DAWN journal is out.

Link

First pictures of Vesta should be taken today.

[antipode]

Hmmmm, cropping Dilo's image, all sorts of interesting things crop up. Crater chains, albedo differences etc. But this caught my eye.



An odd, 'cartouche' like set of grabens? with what looks like a cinder cone? in the middle?
Or just artefacts?

And that arrowed crater with two sections of dark floor - shadows? lava flooded?

This is going to get interesting....

P

[dilo]

The following plots shows the progress of distance and relative velocity during the approach phase, based on mission status updates and, for the last points, on the simulator in the Dawn site (thanks to people who collected snapshot of it in this thread!):


On june 26, Dawn entered the Vesta gravitational sphere of influence (about 125000 km radius, green arrow); however, speed need to be reduced below parabolic-trajectory limit for gravitational capture and orbit insertion. Based on latest JPL press release, this will happen tomorrow around 5:00 UTC at 15900 km distance; this implies a relative speed between 33,5 and 47,5 m/s, adopting a mass of 2,67e20 kg for Vetsa. Even assuming an initially elliptic orbit (indicative insertion speed of 40m/s), current declared speed of 48 m/s implies an average deceleration of 1,3e-4 m/s² which is probably too high unless they use chemical propulsion (ion motor deceleration never went above 6.6e-5 m/s² during approach phase), so I tend to suspect actual speed is lower than declared in the simulator. A confirm of this suspect arises from last Mission Status which declares only 37 m/s on July,13; at 23000km, such a speed would garantee Dawn is already gravitationally captured, even though on a highly elliptic orbit!
Do someone knows more details on incoming insertion maneuver?

[Greg Hullender]

The following plots shows the progress of distance and relative velocity during the approach phase, based on mission status updates and, for the last points, on the simulator in the Dawn site (thanks to people who collected snapshot of it in this thread!):

Why are you so sure there's a strictly linear relationship between velocity and distance from Vesta?

--Greg