Efficient Vall trip?

[Jodo42]

Simply put, is it more efficient to aerobrake at Jool direct from an interplanetary trajectory, which puts you on a Vall encounter, or avoid the aerobrake and slow down entirely with engines at Vall periapsis?

Edited October 11, 2014 by Jodo42

[Boffinbox]

short answer: yes

[Stratzenblitz75]

Well, Its usually more efficient to aerobrake than to perform an insertion burn, especially if you have a very high relative velocity to your destination (for example, a transfer from Kerbin to Jool would leave you with high velocity relative to Jool). However, there is a more efficient solution than just aerobraking if you want to go to Vall. If you aerobrake at Jool and set up a Tylo or Laythe gravity assist, you can reduce your velocity relative to Vall and therefore reduce the Delta V required for an insertion burn (since the orbit after a Tylo or Laythe gravity assist is more similar to Vall's orbit than the orbit after a Jool aerobrake. If that makes any sense).

If you don't want to deal with gravity assists, then yea, in your case, aerobraking at Jool is the best way to go.

[astropapi1]

I've used a combination of Jool aerobraking and Tylo assist before, and that might be your best bet.

[LethalDose]

I think aerobraking at Laythe may be get you the best of both worlds: it should get you captured into the Jool system for minimal dV without having a highly eliptical orbit around Jool.

[Kryxal]

Complicated, though ... aerocapture is easy, there are tools for it, gravity assists are a bit tricky, setting up the nodes can take some work, aerobrake into or during a gravity assist is effectively doing an unspecified burn during or before the assist.

Doesn't MJ have a feature that could help with this?

Edited October 11, 2014 by Kryxal

[cantab]

Definitely aerocapture.

For a Jool aerocapture, this calculator is a big help, http://alterbaron.github.io/ksp_aerocalc/ For a Laythe aerocapture, try setting a very high apoapsis in the calculator, then aim a little higher than it says for that and you should get a Laythe escape trajectory into a decent Jool orbit.

On gravity assists, as an alternative to Laythe or Tylo you can use Vall itself, make an initial flyby that makes your Jool orbit more circular then come back round for another approach. (On a larger scale MESSENGER did this to help it into Mercury orbit.)

[technion]

I've done direct insertions at Tylo which have only taken a fairly small insertion burn - I'm sure that's much better than a Jool aerocapture, after which I'll invariably be on an orbital plane nothing like my target and have a fairly inconvenient intercept. That said, Vall is a lot smaller. I have a feeling the insertion will be quite large, which will change things.

[Laie]

Simply put, is it more efficient to aerobrake at Jool direct from an interplanetary trajectory, which puts you on a Vall encounter, or avoid the aerobrake and slow down entirely with engines at Vall periapsis?

Vall doesn't have all that much gravity to help you, so most of the dV would have to come out of your pocket. Aerobraking at Jool will save you on the order of 1000m/s.

[Hannu]

Vall doesn't have all that much gravity to help you, so most of the dV would have to come out of your pocket. Aerobraking at Jool will save you on the order of 1000m/s.

No, simple Jool aerobraking do not save much (or anything), if you use reasonable transfer orbits. It takes about 1000 m/s or little more to brake staight on Vall's orbit. It takes more to accelerate ship to Vall's orbital velocity after Jool aerobraking. The most optimal way would be aerobrake in Laythe, but it takes so much time and maneuvers (and extra heat shields for DRE) that I do not normally use it to save couple of hundreds of meters per second. You can achieve a moon encounter by using about 10 m/s in mid course correction.