Eve-Kerbin assist to Jool help

[AeroGav]

 

Proof, if any were needed, that  I'm ok with planes, even spaceplanes, but really don't know what I'm doing in a rocket.

Early in a career game, I reckon I can get a good science boost by using a gravity assist to get out to the Jool system ahead of time.    

Unfortunately I don't quite have the skills of this guy -

 

So, according to the wiki - 

 

 

 

I need to launch my probe and lower it's PE within the orbit of Eve to get an encounter.   Then pass behind it to pick up  a gravity assist,    catch another one somehow from Kerbin on my way out to the newly raised AP,  and then bounce between Kerbin and Eve till I raise my AP up to Jool territory.    Profit.

 

Now, when doing a "gain speed" assist the goal seems to be to pass behind the planet as close as possible.   The closer behind , the bigger the assist.  Except that if i get too close to Eve   it bends my flight path too much,   slinging me radially or anti radially with respect to the sun (Kerbol) and the extra energy is wasted.  In fact I've had it throw me straight back on a reciprocal course,  drastically lowering AP.      Is this bad planning or just a limit on how much you can gain from a single pass?

In that diagram from the wiki, the spacecraft is coming in at quite a steep trajectory WRT to the planet.   This allows the flight path to be "bent" greatly, but actually have it work in your favour putting you on a prograde trajectory WRT to orbiting around the sun.    The problem is,  to get this steeper angle when passing Eve,  I'd have to  lower my PE well below Eve's orbit.  Which is very expensive in Delta V terms, more so than just going Jool direct?

 

[Goody1981]

Ahhh I love gravity assists too! Feels like you're doing real mission planning. I recently read this tutorial:

about using a Kerbin assist to get up to Jool. Maybe not quite what you're after, but way easier than planning an Eve-Kerbin-Jool one since you only have to wait for 2 planets to be in the correct relative positions, not 3.

Also, Juno did this and Juno is awesome!

Edited July 11, 2016 by Goody1981

[PLAD]

Flybys are a great way to greatly reduce the dV needed to get to Jool with flybys. You can wing it when searching for the best times to execute a flyby, and if you are willing to orbit the sun several times in the process or make several deep-space maneuvers (DSM) you can usually find something better than a direct Kerbin-Jool flight, but there are two tools that can find the most efficient flybys for you. These are my Flyby Finder and Arrowstar's TOT. These find the specific times that you need to leave a planet and flyby each successive planet in order to go from K to J with only one large impulse, the Kerbin departure burn. (You will always need a few small adjustments along the way, but less than 100m/s should do it, and less than 20m/s with practice.) When setting up these flights the most important thing is to arrange the departure and each flyby to occur at the right time, if you do that the rest falls into place, for instance you adjust each flyby as you approach the planet to be in front of or behind the planet as needed to get the next encounter at the right time. Check out the flights below for details.

There are numerous paths to get from Kerbin to Jool, here's a rundown. For comparison, going directly from K to J takes about 2000m/s when starting from a 75x75km Kerbin orbit. You can also go...

K-Duna-J for about 1950m/s. Use my Flyby Finder or TOT to find these windows. Duna is too small to make much of a difference though.

K-K-J using Juno's flight path for about 1550m/s. Goody1981 gives a link with clues on how to do this, Mad_Maelstrom made a great guide for this.

K-Eve-K-Jool can be done for around 1300-1500m/s depending on the window. FF and TOT can find these. Here is an example of me using FF to execute a KEKJ.

K-E-K-K-J can be done for as little as 1070m/s, or even 1011m/s if you fly by Mun on the way to Eve. Unfortunately this involves a double flyby of Kerbin and neither FF nor TOT can find these. I wrote a spreadsheet that can find them that is in the FF link, but it is a hard search and you might want to use one of the ones I show in my KEKKJ missions.

And by using an exceedingly complicated multi-Mun flyby path I've managed to go from LKO to Jool orbit for 914m/s. This is getting pretty close to the theoretical limit of about 846m/s.

[Firemetal]

Notice that Hazardish used two gravity assists. I doubt you can use one gravity assist to get to Jool but try using two! (Who am I to give people tips on gravity assists? I don't know anything about Gravity assists!)