Pol Landing / general "aim" question -

[cwalrus]

So I'm trying to fly to Pol and back, with a crew of three. I know how to calculate the Dv, mostly.. Esp. with the help of charts... and I know how to rendezvous with a target.

But STILL... I can't seem to get to Pol without burning WAY more DV than I find in the online charts. Like 4k to line up with it even upon approach to Jool.

Here's the frustrating thing: I know what I'm doing, sort of. I have Mechjeb, and I'm not afraid to use it. But even with my own knowledge of rendezvous strategy, and using Mechjeb's "fine tune to 20 KM to target" etc, etc, etc ....I STILL can't get lined up.

What are some good tactics for hitting Jool's moons, or any kinda thing in that realm? Here's what I know, so no need to repeat it:

Use Porkchop transfer from Mechjeb to find the right date and angle to get to Jool.

Once you're on the way, check your encounter- the sooner you make changes the better, fuel-wise.

If you make it into Jool orbit, you can treat Pol like a "target" and sync up your AN's / i.e. your respective inclinations... but even at this point this may be prohibitive.

So I guess here's the question: You're approaching Jool. What's the most DV efficient way to land on it's moons? How do you decide whether Aerobraking is a good plan for you or not, etc?

[n0xiety]

Aerobreak at 198km-195km jool atmosphere depending on your ship design and get into very high jool orbit. After that transfer to high jool moons should be very easy. You can always aerobreak at Laythe atmosphere which will cost you less dV in the end since you will be in a higher orbit than jool aerobreak.

[RocketPropelledGiraffe]

Always consider gravity assists on Jool's moons be captured to a high Jool orbit. It will save you a lot of Delta-v, it is far less dangerous and more predictable than aerobreaking, plus it can also do the necessary inclination changes for cheap.

Additionally: Bouncing about Jool's moons is one of the most enjoyable things in KSP, but maybe that's just me.

[Old Foxboy]

Hello,

just in case you didn't do it already: Make sure you enter the Jool system PROGRADE (counterclockwise), so you don't fly the other way round Jool than all the moons. If you can hit it in the first run, don't aerobrake at Jool but at Laythe. Much safer. As for Pol, treat it like Minimus. Pol won't help you much with it's gravity (because there isn't much), so try to encounter it at your Jool orbit apoapsis where you are as slow as possible.

As for the porkchop: Are you sure you selected the minimum Delta V option?

[cwalrus]

See these are great answers - which leads me to ask, HOW do you know this?? Just experience? I enter Jool's SOI and just start pulling maneuvers.. hoping for some magic ... but I'm doing it blind.

The 'encounter Pol at your AP' tip is great, and makes sense, and I might have figured that out eventually...same with Enter Jool 'prograde'.... but the other tips? Just trial and error?

Thanks by the way!

And yes, I'm using porkchop's min. Delta V. I have that figured out at least....

The question i have boils down to "How do you fly around Jool's system the most efficiently.. without blindly setting up Maneuver nodes"

[Lelitu]

The question i have boils down to "How do you fly around Jool's system the most efficiently.. without blindly setting up Maneuver nodes"

The actual question has nothing to do with Jool at all.

It's far more about what the different axes will do to your orbit.

There's some wonderful guides on the forums about orbital maneuvering. But practice with a maneuver node really is the best way.

Make a node somewhere in a stable, slightly elliptical orbit. set a maneuver node somewhere (doesn't actually matter where). You'll need to do this at a few points.

Now start adjusting the different nobs on the burn, and see what it does to your orbit. Recreate the node after each change, so it's setting from 0 each time.

With practice, you'll get to see that burning prograde at a point, raises the opposite side of the orbit (and may move apo/peri apses).

Radial/anti-radial twist the orbit around the body being orbited,

and normal/anti-normal change plane.

For efficiency, there are three things to remember: Aerobraking, gravity brake/boost, and transfer windows.

Just like in the main system, there are transfer windows between jool's moons. For exactly the same reasons.

[cwalrus]

Awesome answers - I knew what the different handles on the nodes do, but pointing out that there are transfer windows b/w Jool's moons points me in the right direction...!

[Lelitu]

Awesome answers - I knew what the different handles on the nodes do, but pointing out that there are transfer windows b/w Jool's moons points me in the right direction...!

As far as getting around jool goes, it's the kerbol system in miniature

and fortunately for all of us, without recursion.