Tylo Laythe gravity assists

[antipro]

I have to put some relays in a 14Mm Jool circular eq orbit.
I created, manually and not easily, a node that intercept Tylo and Laythe,
beacuse in my mind this is the best way to save dV, but I'm certainly not sure.
The result orbit Pe is at 14Mm, then I'll circularize.

Is there another way in order to save more dV? or just simpler to perform?
the probe was not built to perform aerobrake maneuvers.

Edited February 23, 2021 by antipro

[The Aziz]

I think you could make few revolutions around Jool with Pe near Laythe and plan the flight path so you get few slowing encounters along the way - the same way as IRL interplanetary probes use multiple Earth flybys to get somewhere. Just make sure that you don't go too close to other moons. It will probably cost some fuel but hopefully less than full circularization burn.

[antipro]

9 minutes ago, The Aziz said:

I think you could make few revolutions around Jool with Pe near Laythe and plan the flight path

Are you saying: I do Tylo gravity brake into elliptic orbit, i.e. Ap 200Mm - Pe close to Laythe orbit, then I do multiple Laythe gravity assist to brake more? I could try.

 

15 minutes ago, The Aziz said:

 so you get few slowing encounters along the way

I can't get this: few than two?

 

19 minutes ago, The Aziz said:

Just make sure that you don't go too close to other moons.

this could be a problem.

[The Aziz]

1 hour ago, antipro said:

Are you saying: I do Tylo gravity brake into elliptic orbit, i.e. Ap 200Mm - Pe close to Laythe orbit, then I do multiple Laythe gravity assist to brake more? I could try.

I based this on the trajectory in the picture. You seem to get an assist from Tylo that sends you to an encounter with Laythe. So it's good because your target orbit is not far away from there. Not sure what's your Jool Ap after this because the screenshot doesn't say it, but yes, you could try performing a maneuver nearby Laythe Pe, so that when you are close to it again, you can get another assist and so on.

And yeah avoiding moons may be tricky, but what else can you do.

I see another problem, but that shouldn't matter at this time - your target orbit looks uncomfortably close to Laythe, after few days this probe is probably gonna hit something or be ejected out of the system.

[king of nowhere]

4 hours ago, antipro said:

I have to put some relays in a 14Mm Jool circular eq orbit.
I created, manually and not easily, a node that intercept Tylo and Laythe,
beacuse in my mind this is the best way to save dV, but I'm certainly not sure.
The result orbit Pe is at 14Mm, then I'll circularize.

Is there another way in order to save more dV? or just simpler to perform?
the probe was not built to perform aerobrake maneuvers.

you already got an excellent trajectory. you are using only gravity assists to go from a flyby to a trajectory that has your desired periapsis and apoapsis at laythe for free. there is literally nothing more than that you can save with gravity assist. you can't lower your apoapsis below laythe when you are doing a laythe flyby.

however, i question the wisdom of your target orbits. those are not good orbits for relays. they will get eclipsed by jool, or by some other moon, all the time. for jool relays, i would use a high polar orbit instead. then again, a polar orbit also gets blocked when your relays are on the wrong side of the ecliptic plane.

[antipro]

2 hours ago, The Aziz said:

I see another problem, but that shouldn't matter at this time - your target orbit looks uncomfortably close to Laythe, after few days this probe is probably gonna hit something or be ejected out of the system.

According to wiki, Laythe's SoI radius is 3723646m and it orbits at 21184000m.
So 21184000m - 3723646m = 17.460.354m > 14Mm.

 

1 hour ago, king of nowhere said:

you already got an excellent trajectory. you are using only gravity assists to go from a flyby to a trajectory that has your desired periapsis and apoapsis at laythe for free.

uhm.. ok, but as I said is very difficult to reproduce it, it needs to play with many numbers after the comma.
and moving trajectories and bugs apart.

 

1 hour ago, king of nowhere said:

however, i question the wisdom of your target orbits. those are not good orbits for relays. they will get eclipsed by jool, or by some other moon, all the time. for jool relays, i would use a high polar orbit instead. then again, a polar orbit also gets blocked when your relays are on the wrong side of the ecliptic plane.

3 relays at 14Mm never get eclipsed apart perhaps only sometimes when one of those 3 inner moons are aligned.
I already have other 3 relays at 220Mm, I did test both constellations and they seem fine, I do not think is a problem.

Edited February 23, 2021 by antipro

[king of nowhere]

1 hour ago, antipro said:

uhm.. ok, but as I said is very difficult to reproduce it, it needs to play with many numbers after the comma.
and moving trajectories and bugs apart.

impossible to avoid. you are coming from very far, a small difference in thrust will make a large difference in your trajectory around tylo. and then you get a gravity assist from tylo, and a gravity assist magnifies any small difference in trajectory. in my kerbalism grand tour i make a similar path around jool, where i have two ships coming from the same direction and a difference of less than 1 m/s in entering jool's SoI changes the gravity assist so that one goes to laythe and the other goes to Pol. and finally, you have a third gravity assist from laythe; all the careful alignment is further magnified. it's like bouncing a ball around two obstacles; the smallest change of trajectory will make a big difference in the first bounce, which will entail an even bigger difference in the second.

 

on the plus side, you do not need to carefully align everything. as long as your first gravity assist gets you to laythe, a small course correction manuever afterwards will suffice to put you back on the right path.