Get to Pol without Jool Orbit

[ianr15]

Hello to all of you,

I would like to send a science mission to Pol. An easy way to do this would be to transfer to Jool, go in (low) Jool orbit and then make a transfer to Pol. This is rather fuel-expensive, and I have read somewhere that you could go to Pol without a (low) Jool orbit. Unfortunately, it didn't mention a link to a tutorial. I couldn't really find one myself either, even not a more abstract interplanetary moon mission tutorial.

Does anybody of you know how to do a more fuel-effecient mission to Pol?

All help is highly appreciated.

Edited August 5, 2014 by ianr15

[DrMonte]

So don't go "low" and that is all the trick.

First fuel economy comes from the point that you have to stop your ship from escaping Jool orbit. There are few ways to do this and you can think of your own too:

1. We can call it straight. Lower Jool Pe up to some 200km and at the Pe point burn till you have the orbit. Lower Pe as early as you can so it will require just a few dV. You can have elliptical orbit and catch-up with Pol at some time.

2. Silliest thing Kerbals ever invented - Aerobraking. Similar to 1st. Except that you lower your Pe to ~100km and do not require to retro-burn at Pe. Then just sit and pray. You get fun and fuel savings.

3. Super hard but even more fuel saving - ahead body meeting. I think this is what NASA does. Idea is to meet a heavy Mun (Laythe, Vall, Tylo) heading at you. This maneuver will put you in any orbit you want with minimum fuel use and in safe way.

Common principles are:

- The earlier you burn the less fuel is required;

- Burn to raise your orbit at Pe, burn to lower your orbit at Ap;

[ianr15]

Thank you very much DrMonte for your reply. I was indeed thinking that the (very little) information I got was refering to option 3. I hoped that there was an easy way to do this. Option 2 was my alternative method. I hope I can find something on ahead body meeting. Again, thanks for your reply.

[Superfluous J]

One trick I've found is to use PreciseNode, and tweak your prograde/retrograde/radial thrusts to modify how long it'll take to get to your target (I suggest Tylo. It's big and far from Jool). Do this after you've done the Normal burn. You can do it right after you complete that and it'll probably only cost a few m/s of dV. Just keep playing with the PreciseNode +/- buttons while focused on Jool, and watch how they affect your ship's trajectory. Keep it near Tylo's orbit and as you change the time of arrival eventually you'll get a Tylo intercept.

Then thrust limit your engine down and make that maneuver burn as precisely as you can.

[ianr15]

Thank you very much for your reply 5thHorseMan. I don't have access to a computer at this moment (using my phone now), but I'll try it as soon as I can. But it sounds like a plan.

[Kasuha]

Set up your Jool encounter (entering Jool SOI), exit Kerbin SOI and then you can use small burns and RCS to fine-tune your approach. Just set up your trajectory so it misses Jool with periapsis at approximately Pol's orbital altitude. If you're lucky (or smart) you can even set up direct encounter with Pol as you can change the time of arrival to the system by weeks using radial burns. If you're not coming in Jool's equatorial plane, though, you may want to use Tylo gravity slingshot to align your inclination with Pol's first. Or you can just align the plane during your braking maneuver.

[Kobymaru]

Does anybody of you know how to do a more fuel-effecient mission to Pol?

I don't think that a direct entry into Pol orbit is the most fuel efficient, because you have to do always do your entry burn, otherwise you'll just fly right out of Pol orbit and then Jool system.

Additionally, it's super hard to hit Pol because of the inclined orbit.

The most efficient is probably a Tylo slingshot with or without a Jool aerobraking maneuver.

[DrMonte]

I need to know more about that. I didn't find anything when googling "ahead body meeting". Would you care to explain?

That would be the same slingshot. Slingshot is used for slowdown and no more braking at Jool orbit is required.

[Laie]

I need to know more about that. I didn't find anything when googling "ahead body meeting". Would you care to explain?

Don't know if "ahead body meeting" is a proper name, but he means what you're inquiring about in your first post: going to a moon directly, without entering into a proper orbit around the planet first. Kasuha and 5th Horseman have basically already ansered how to do it:

1 Set up & execute Jool encounter

2 leave Kerbin SOI

3 twiddle and tweak with manouvers until you get an encounter with your destination moon. Delta-V changes are probably miniscule; consider using RCS instead of your engines.

It's basically the same as setting up an encounter with a planet, but requires much higher precision -- even with tools like precise node, you may be twddling and fiddling for a long time until you get the encounter you want.

Like 5th Horseman, I suggest you don't even try to hit Pol. Pol is a tiny target. Go for the much bigger Tylo instead. Transferring from Tylo to Pol is comparatively cheap. Also, once in orbit around any Joolian moon, you have the others to give you gravity assists. The Joolian system is like a pinball machine.

And keep in mind Variant 2: goo to Jool, aerobrake, and do not enter into a low circular orbit. Remain in an highly eccentric orbit. That costs you less than 100m/s so far. Then wait for an opportunity to present itself... it won't be long. You should be able to get to Pol with less than 1000m/s, probably much less.

[ianr15]

Thank you for all your answers. I used a combination of your answers, but the general method was Laie's variant number 2 (or the equivalent suggestions from other people.) I got to Pol without having to spend ridiculous amounts of delta v. I had a special reason to go to Pol, so I didn't go to Tylo, which would indeed have been a lot easier. 100 percent mission succes, so I will mark this thread as answered. Again, thank you all, your help is highly appreciated.