[X] My Assistant

[pioneer]

According to this press release, Cassini will fly 25 Km from the surface of Enceladus in October I know the escape velocity of Enceladus is low, but just how close can Cassini come to the surface without the gravity pulling it in? What is the escape velocity of Enceladus?

[mchan]

Chen-wan L. Yen

E.g., ref http://adsabs.harvard.edu/abs/1989JAnSc..37..417Y

Her work merited the naming of minor planet 9249 after her. From the citation in Dictionary of Minor Planet Names:

Chen-wan L. Yen, a senior analyst within the Mission and Systems Architecture Section of JPL. ...using multiple-impulse and gravity-assist techniques, her optimized interplanetary trajectories have allowed significant payloads to be launched within current launch vehicle capabilities. Her work is evident in the interplanetary trajectories designed for Galileo, Magellan, Cassini, and Stardust.

Note the "reverse delta-V/gravity assist" decrementing resonance orbits technique used for Messenger can also be seen in the trajectory to get the earlier Europa Orbiter to the point of a minimum delta-V maneuver to enter Europa orbit.

[remcook]

Remcook, I think your calculation missed the fact it's 1000 km altitude above Titan!

No, that was taken into R1 (=Rt+ht), just like R2 = Re+he
I maybe used slightly different values for mass.

[jmknapp]

According to this press release, Cassini will fly 25 Km from the surface of Enceladus in October I know the escape velocity of Enceladus is low, but just how close can Cassini come to the surface without the gravity pulling it in? What is the escape velocity of Enceladus?

For this flyby, at 54 km altitude, the escape velocity was 218 m/sec. At 25 km it would be a bit more, 228 m/sec. (Surface escape velocity is 239 m/sec.)

So given that it was going at 18,000 m/sec for this flyby, the escape velocity is in the noise.

[scalbers]

I think the hypothetical gravity calculation for the interior of Enceladus should take into account the fact that gravity decreases in the interior compared with the maximum value reached at the surface. Hence there would be no gravitational advantage to considering an interior flyby.

When you are inside a roughly spherical world, only the radius interior to where you are ends up giving a net gravitational attraction.