Tour of Jool, Use Slingshots.

[davidpsummers]

I have a probe at Jool. I Aerobroke (braked?) and have an orbit with the 100 km periapsis and an apoapsis around the orbit of the furthest moon (~170,000 km). I have 2100 m/s to burn but my orbit is inclined ~5-7 degrees wrt the plane of the Jool system. I think if I'm going to swing by all the moons (orbits aren't going to be possible) I will need gravity assist? What do I do, set up the encounter with Pol and then arrange it so it points me at the next moon? How do I arrange that? Any systematic way or do I just try things? It seems space is kinda big for that approach?

Edited August 8, 2014 by davidpsummers

[Laie]

Swinging by all the moons in one go? I won't say it's impossible, but suggest you try something else.

If you're content with very eccentric orbits around the moons, you can get from moon to moon at about 300-500m/s each time. You'll have to bide your time before you can move on, but it isn't difficult. I can't gurantee that you can make it to all five moons, but the four that are about on the same plane are certainly possible. Skip Bop at first -- if you have enough dV left in the end, you may as well reach it from Pol; and the plane change will be much cheaper, too.

Talking about plane change, you can use every encounter to effect a plane change as well. You may try to meet the plane of the moons during your first encounter; alternatively, try to make it so that after your encounter, the AN/DN sit as close to the apses (apsises?) as possible. Doing a plane change near a far-out apoapsis is quite cheap. And there's always the possibilty of not doing a plane change at all. You'll have to wait much longer for a good encounter.... but if you don't mind spending a few years in timewarp, something is bound to come around.

Finally, nothing prevents you from combining all of the above.

[Kasuha]

First, go to your config file and increase number of conic patches visible if you have not done it yet. You're definitely going to need that to plan gravity slingshots.

Second, set Laythe as your target and put a burn at one inclination point (the one closer to Jool) to get the other inclination point to meet with Laythe. If you don't get an intercept immediately, try it an orbit later. Or two etc. And you can of course to adjust your orbital period a little prior to the main burn to get the intercept exactly at the inclination marker.

Then just fiddle with the maneuver and watch what your trajectory is doing. You can easily get a Vall/Tylo intercept, or at least trajectory crossing path of either of these moons just by flying past Laythe.

And you definitely can fix your inclination on that pass just by adjusting your Laythe approach by a few m/s north/south at the right point (about halfway between your 'ejection' and Laythe intercept).

Your 2100 m/s should be more than enough to get all intercepts and return to Kerbin if you do it right.

[technion]

The thing that just about kills me in touring Jool, is the inclinations. I would transfer from Tylo to Laythe, and end up in a highly inclined orbit. From there, the next transfer can only be done in an expensive version.

[Kasuha]

The thing that just about kills me in touring Jool, is the inclinations. I would transfer from Tylo to Laythe, and end up in a highly inclined orbit. From there, the next transfer can only be done in an expensive version.

1/ you don't need to fix your inclination if you set up your intercepts at inclination points

2/ inclination can be always fixed using gravity slingshot. Also if you land, you can launch at any inclination you need next.

[cantab]

Pol is too light to give much of a gravity assist, but if you fix your inclination near Jool apoapsis and you're still on that eccentric orbit you're bound to hit one of LVT sooner or later. Make small corrections in Jool orbit to tune your gravity assists, and I agree with doing Bop last.

[davidpsummers]

Thanks for the replies...

-I was thinking of doing Pol first and working my way in, since I can use Jool to aerobrake. But people are suggesting Lythe first and slingshoting out (because it is bigger?)

-It sounds like it is easier to change inclination at the apoapsis rather than the periapsis? But if burn near Jool, I can to the minimum needed to get an intercept?

[Yasmy]

Inclination changes can be trivial when going between moons. It is not like changing your inclination when you are in a stable orbit.

Once you have an intercept with a distant moon, small normal (out of plane) adjustments greatly change the latitude of your swing-by, which will greatly change the inclination of your orbit once you exit the moon's SOI. It's the same as adjusting your inclination around a planet from far away on an interplanetary transfer trajectory. Tiny out of plane adjustments make huge changes to your exit inclination.

[Kasuha]

Thanks for the replies...

-I was thinking of doing Pol first and working my way in, since I can use Jool to aerobrake. But people are suggesting Lythe first and slingshoting out (because it is bigger?)

The real reason is that when you'll aerobrake at Jool, you'll end up with a very low periapsis. Raising it up all the way to Pol is unnecessary spending of dv if you can just aerobrake your apoapsis to Laythe and have the first encounter almost for free.

-It sounds like it is easier to change inclination at the apoapsis rather than the periapsis? But if burn near Jool, I can to the minimum needed to get an intercept?

If you are changing inclination in orbit, it is definitely less dv to do it at the higher altitude because your orbital speed is smaller at that point and thus it doesn't take that much to change it.

But if you can use gravity slingshot you can do it almost for free as described above.

[davidpsummers]

The real reason is that when you'll aerobrake at Jool, you'll end up with a very low periapsis. Raising it up all the way to Pol is unnecessary spending of dv if you can just aerobrake your apoapsis to Laythe and have the first encounter almost for free.

I guess I'm missing something. I have a low periapsis but I don't plan on raising it at all? I adjust until I encounter a moon and slingshot. That is the same for Pol and Lythe?

(BTW, I think I can get an encounter with Lythe without lower the apoapsis. I assume that is fine, as long as a I don't fly by it too fast to get enough of a slingshot?)

[davidpsummers]

OK, I played around with it. I seemed to, regardless of the periapsis and apoapsis, get a Lythe encounter which just needed to be tweeked to lead to a Pol encounter. (And after each encounter, my previous orbit doesn't matter much). After Lythe, I try to tweak my Pol encounter to lead to another one. If I get the same moon again, I just fly by it and use it to get to another.

Encounters where I get to be "near" Lythe tend to lead to escape velocities or being thrown into Jool, so I guess I'll have to keep trying on that. Maybe save the for last. (I have a lander I want to drop in there on the way anyway).

[technion]

1/ you don't need to fix your inclination if you set up your intercepts at inclination points

2/ inclination can be always fixed using gravity slingshot. Also if you land, you can launch at any inclination you need next.

Maybe I worded it poorly.

If I'm sitting in a polar orbit of Tylo, and luck would have it that, at what would otherwise be a great time for an ejection point, that orbit is perpendicular to Tylo's orbit, odds are it's going to be a multi-step transfer.