Best way to approach and capture at Jool for outer moon mission?

[moogoob]

Okay, long story short is I've just launched, in career mode, my second Jool lander probe. This one is supposed to complete Explore contracts for Pol and Bop. Now, I've done the approach to Jool many times before, but this time I'm curious - what is the best way to approach the system's outer moons? I see two options:

1. Bi-elliptical-style transfer, where you fly in close to Jool to maximize Oberth effect and fire your engine until your periapsis is near where your target orbit (I think I'll do Pol first) is, then do what you have to do to reach the moon in question.

2. The "Casual approach", where you put your approach periapsis near your target moon's orbit (or so), then burn to circularize. This seems easier, at least at first glance.

So, does anyone know? Also, would a high-speed (al-la New Horizons) trajectory have an impact on how you capture?

Edited September 28, 2015 by moogoob
Got it answered. Thanks guys!

[Red Iron Crown]

The answer to captures at Jool is almost always "use a Tylo slingshot". Use the slingshot to capture, fix inclination, and place your Ap near the first target, then at that Ap burn to get your intercept.

[Foxster]

+1 on wot RIC said. Laythe is a good second bet for this.

[Slam_Jones]

+1 on wot RIC said. Laythe is a good second bet for this.

Just make sure you're not aerocapturing on Laythe going the wrong direction... you'll be going about 7km/s, which is basically instant explosion (if coming directly from Kerbin, at least).

[Superfluous J]

Don't aerocapture at Laythe, do a slingshot to slow yourself down.

The reason Tylo and Laythe slingshots are better than aerocapture at Jool is twofold:

1) You don't have to aerocapture. Your ships will not explode, and you can be (fairly) sure the orbital paths predicted by patched conics will be true. You can - from KERBIN - nail a Pol or Bop encounter (though getting your resultant Jool orbit up near them is really the best you should try for).

2) When you leave Laythe or Tylo, your Jool periapsis will be a bit higher than it would have been after an aerocapture, so the eventual burn out at Pol or Bop will be all the lower for it. Not only is a Tylo slingshot easier, it's cheaper! Not too many of the easy ways are cheaper in KSP. Revel in this.

[moogoob]

Question regarding Tylo/Laythe slingshot - what if it's on the wrong side of Jool? How would that work?

EDIT: and you're all correct in thinking I don't want to aerocapture - I certainly didn't bring any heat shields.

[SpeedDaemon]

Question regarding Tylo/Laythe slingshot - what if it's on the wrong side of Jool? How would that work?

EDIT: and you're all correct in thinking I don't want to aerocapture - I certainly didn't bring any heat shields.

If you're still a ways out from the Jool system, it should be pretty easy to adjust your arrival time to get it to work.

If you're already in-system, it might be a bit harder, depending on how far out you are, but you should still be able to fiddle with a node to see if you can get the timing to work out for a reasonable amount of dV.

EDIT: (usually, I have trouble *avoiding* encounters that I don't want...)

Edited September 28, 2015 by SpeedDaemon

[Superfluous J]

Question regarding Tylo/Laythe slingshot - what if it's on the wrong side of Jool? How would that work?

EDIT: and you're all correct in thinking I don't want to aerocapture - I certainly didn't bring any heat shields.

The beauty of getting to Jool is it takes a LONG time, and you go a LONG way. If you slow down or speed up or burn radially just a few DECIMETERS per second, you can change the time you close approach Jool by DAYS.

So where Tylo and Laythe are when you get there is TOTALLY up to you. Just get your Jool Pe near their orbit and then tweak the prograde/retrograde/radial markers until you get an encounter. Then tweak them more until when you exit the moon's SOI, you're orbiting in a way that is satisfactory to you.

[moogoob]

Thanks you two! I'll give it a shot - the mission just launched and I was going to do some Mimnus grinding and other near-Kerbin infrastructure upkeep while it works its way out to Jool. Thank goodness for Kerbal Alarm Clock!

[Red Iron Crown]

The beauty of getting to Jool is it takes a LONG time, and you go a LONG way. If you slow down or speed up or burn radially just a few DECIMETERS per second, you can change the time you close approach Jool by DAYS.

So where Tylo and Laythe are when you get there is TOTALLY up to you. Just get your Jool Pe near their orbit and then tweak the prograde/retrograde/radial markers until you get an encounter. Then tweak them more until when you exit the moon's SOI, you're orbiting in a way that is satisfactory to you.

Truth here. My preferred technique is to burn and get an encounter with Jool from LKO, then wait until I've exited Kerbin's SoI to make a correction burn to refine it so I encounter Tylo (or Laythe) exactly how I want.. As 5th mentions, these burns are quite small, so I use PreciseNode (which also lets you edit the node while zoomed in on your target) and thrust limit the engine(s) for greater precision.

[moogoob]

I just wanted to bump this thread to thank you all. It worked perfectly! 1000m/s burn at 50km above Tylo was all it took to make my periapsis within pol's, AND match 95% of pol's plane. VERY nice, considering I both took a fast transfer route (so had excess energy to bleed off) and came into the system from slightly opposite Pol's inclination.

Once again, thanks! This now feels like the pinnacle of my KSP accomplishments.

[Red Iron Crown]

Congrats, getting a slingshot just right is really satisfying, it's like you're bending the forces of nature to your will.