[azernik]

It can reduce the delta-V requirements, though - by the same principles as a gravity assist, a capture burn (especially into a loosely-bound planet-centric orbit) often takes less work than burning into the equivalent heliocentric orbit on your own.

[JumpCrisscross]

> by the same principles as a gravity assist, a capture burn

Note to the audience: these mechanisms don’t violate the conservation of energy because you aren’t tapping the object’s gravitational energy per se but instead its orbital energy around the sun. Put another way, you can’t do a gravity assist or capture burn in any direction.

[azernik]

The usual way I explain it is as a transfer of kinetic energy and momentum from the large body to the small one. The interaction is through gravity, rather than the mix of electrostatic, degeneracy, and strong/weak forces involved in collisions; but the equations are more or less the same.

(Usually textbooks use a baseball bouncing off a semi truck to illustrate.)

[beckingz]

Right! The Oberth effect for a smaller body is not as large as it would be for earth, but would still be non-zero.

[lmilcin]

"Non-zero" is the key word here.

Oberth effect from fast flyby of a body with low gravity would be negligible.

[a1369209993]

> Oberth effect from fast flyby of a body with low gravity would be negligible.

Pretty sure the problem would be, rather, that a flyby of a body with low gravity would be negligibly fast (relative to your speed when not flying by). Oberth effect is because of high speed (a given increase in momentum gives more kinetic energy at higher speed than at lower speed) - it's just that dipping deep into a gravity well is the obvious way to get that speed.

[jessriedel]

Ok, good point. Thanks.

[azernik]

Still definitely not worth it for something so small, though!