2 Pallas Options

[Paolo]

no one seems to have noticed this
http://www.sciencemag.org/cgi/content/abstract/326/5950/275

[nprev]

Pallas is not nearly massive enough to effect a significant change in Dawn's velocity nor change its inclination. Recall that the only moon in the Saturn system massive enough to affect Cassini's trajectory is Titan...and Pallas is only about twice as massive as Enceladus.

If this happens at all, it's gonna be a flyby.

[HSchirmer]

Pallas is not nearly massive enough to effect a significant change in Dawn's velocity nor change its inclination. Recall that the only moon in the Saturn system massive enough to affect Cassini's trajectory is Titan...and Pallas is only about twice as massive as Enceladus.

If this happens at all, it's gonna be a flyby.

Ahh, good point, interesting point actually, seems that gravity assist maneuvers are limited to about 70% of the escape velocity of the object.
While Pallas is moving fast, (relative to Dawn) it's weak gravity only lets you take small bites of that gravity assist capability.

So, Pallas escapeV is 324 m/s, so the maximum deltaV from any single assist is around 230 meters per second.
As compared to Titan, the reported gravity assist numbers I could find for Cassini had a deltaV of 1,100 meters per second.
That initially seems promising, Dawn at Pallas might get around 1/4 of the slingshot effect of Cassini at Titan,
but part of the benefit to Cassini is that Titan has a 16 day orbit, so get to do multiple slingshot encounters.
Interesting that Titan's orbit has a relative motion available for slingshot manoeuvres of around 5.6km/s.
For Dawn in a solar orbit, the relative motion of Pallas around the Sun is much higher, around 17.6km/s,
but the orbit takes so much longer, 16 hundred days, you're not getting many slingshot opportunities.

So, at first glance, it seemed like Pallas' high speed might balance out its low gravity for gravity assist,
but the way the equations work out, the speed of Pallas doesn't translate into higher deltaV, at least for single passes.
With each orbit taking 4.6 years, it would take a long while to do multiple passes.