Return to Kerbin from Tylo orbit help

[AeroGav]

Hey  folks,

my Jool-5 mission is nearing it's end,  but I'm not sure i can get home :-(

I'm currently in a low orbit of Tylo with about 1300 dV.     By waiting till I'm on the night side of Tylo, and Tylo is also on the night side of Jool, I can make a  burn of about 800 dV that ejects me prograde to the Jool orbit, and another 10 or 20 m/s or so sees me kicked out of the Jool system retrograde with respect to Jool's orbit around the sun.          The problem is, I then only have about 420dV left, and if I retro burn at my AP around the sun,  this only brings my PE down to Dres - but no chance of an encounter due to Dres' highly inclined orbit.

I'd need another 1100dv or so to bring me down to the altitude of Kerbin's orbit - unless there are any smart gravity assists you guys know about?

 

Other than genius gravity assists,  my options seem to be

1) launch a refuel mission -meet it halfway in the Dres system

2) go back to an earlier save and refly the last couple of moons of the Jool challenge to try get more delta V for the home bound trip.

 

[Hodari]

You'll probably want to wait until Kerbin and Jool are in the correct relative position to each other, do your first burn(Tylo ejection) so that you end up as close to Jool as possible without actually entering its atmosphere and then combine your ejection from Jool and transfer into a single burn from there so you take advantage of the Oberth effect.  If that's still not enough, then maybe you could get some sort of gravity assist from Jool's moons from there, but that will be much more difficult to plan out.

[Shadowmage]

Jool is an excellent system for gravity assists.  You might be able to do something like a Tylo -> laythe -> Tylo assist to lower the cost of the initial ejection and maybe even bring your solar pe closer to kerbin.  Both laythe and tylo have sufficient gravity for decent assists.  Tylo is probably better as you can scrape down to <20k for maximum effect (whereas laythe has an atmosphere that keeps you from going quite as close).

Been so long since I've played around with the moons though, that suggestion is about all I can offer (have no hard data on what might work / not work).  I know I've used similar for captures in the past (playing moon-pinball), and you should be able to save some fuel for an ejection, at the cost of time (waiting for things to line up).  Don't forget that you can also do 'assisted' gravity assists with small burns at pe...

[WanderingKid]

Well, I'm sure you checked the transfer window planner, but the best dV transfer in Alex Moon's setup is 4,933 or so, figure rounded to 5k.  So there's certainly no obvious way.

Thinking it through, you would usually need ~1,200 - 1,400 to circularize at Kerbin.   Assuming Aerobrake, that gets you down to ~3,600. 

If you can pinball wizard yourself to a grav assist from Tylo, then intercept and grav assist again at Laythe during your outbound trajectory, you could possibly spin up enough dV to make it, but I have absolutely no idea how to aim that double boost intelligently.

[AeroGav]

41 minutes ago, Hodari said:

You'll probably want to wait until Kerbin and Jool are in the correct relative position to each other, do your first burn(Tylo ejection) so that you end up as close to Jool as possible without actually entering its atmosphere and then combine your ejection from Jool and transfer into a single burn from there so you take advantage of the Oberth effect.  If that's still not enough, then maybe you could get some sort of gravity assist from Jool's moons from there, but that will be much more difficult to plan out.

What, so

1) eject from Tylo in a direction that's radial inward, or

2) actually eject retrograde to the Jool orbit to get down lower , even though the next step is to burn prograde to eject from Jool system?

Surely 2) would be like going from Minmus to Duna by heading back down to LKO before making the transfer burn to Duna, despite the oberth effect you're better off not burning retro so that you can then burn prograde?

Assist from Laythe sounds nice if i can work it..

[Gordon Fecyk]

Remember that we could capture at Jool using Laythe twice. You can do something similar outbound by passing behind Laythe twice once out of Tylo's influence. That would get you out of Jool's SOI at least. If you really need to, you could pass in front Jool itself on another (granted, really long!) orbit to slow down with respect to the sun.

I took a crack at it once but like you only managed to scrape Dres' orbit. But I wasn't all that patient; I could have lowered my sun PE just enough to plan another Jool encounter, then pass in front of it.

I'd again suggest taking a look at Hazard-ish; he used two Jool assists to get an ion-powered Segway down from Eeloo of all places, then passed in front of Eve and Kerbin a few times to slow down further. It looked like he too could only descend to Dres' orbit on the first pass.

--

Edited February 3, 2017 by Gordon Fecyk
I got the front / behind order wrong

[WanderingKid]

I'm confused, bear with me, it's not entirely a shock.  I fired up a little ship and hyper-edited it into Tylo orbit.  MK1, Parachute, Heat shield, decoupler, FL-T200, and a Terrier.  Came in with about 1,298 m/s dV, so I figured it'd be a fun toy.  Stuffed it into orbit around Tylo at 45k alt.

Using Phase Angles and manipulating orbit departures, I can do a direct burn from Tylo to Kerbin orbital height for ~1,095 m/s. 

 

 

However, manipulating this requires getting the phase angle right.  It takes 2 years + 110 - 230 days (roughly) for the return.  A Kerbal year being... um... errr... 426 days.  So, roughly 2.25 - 2.5 years to return.  Which means the phase angle needs to be in the right position for the trip.  I used this to get an idea where to have Tylo (and what side of Tylo) to figure out where to depart from it at, which is roughly 20-30 degrees just past prograde for Jool:

http://ksp.olex.biz/

It's doable, but you'd have to spend a bunch of time exploring maneuver nodes and departure dates.

Edited February 3, 2017 by WanderingKid
Spoiler tags having fun with me...

[Aegolius13]

6 hours ago, WanderingKid said:

Using Phase Angles and manipulating orbit departures, I can do a direct burn from Tylo to Kerbin orbital height for ~1,095 m/s. 

I did some quick-and-dirty trial ones, and I got an ejection burn of about 1040 to go from 50km Tylo to a Kerbin orbital intercept. I didn't hit the perfect ejection point, so it could probably go a little lower - maybe around 1000 m/s.  That's the general figure I've seen in past returns from Laythe as well.   OP, if you're getting a total needed burn of 2400, you may want to try timing it at some different points in Laythe's orbit around Tylo.  Agree the spot looks like about 20-30 degrees before the middle of the night side.  So you might have enough fuel, but it will likely depend on getting the plane change right, since you won't have much to burn on a mid-trip plane correction.  As far as other tricks, I've never tried outbound gravity assists around Jool's moons.  Should work in theory, but would be very hard to aim.  An assist around Jool itself should give you plenty of delta v, but could take a long time.  You could couple that with a braking assist around Kerbin or Eve.  

[AeroGav]

8 hours ago, WanderingKid said:

I'm confused, bear with me, it's not entirely a shock.  I fired up a little ship and hyper-edited it into Tylo orbit.  MK1, Parachute, Heat shield, decoupler, FL-T200, and a Terrier.  Came in with about 1,298 m/s dV, so I figured it'd be a fun toy.  Stuffed it into orbit around Tylo at 45k alt.

Using Phase Angles and manipulating orbit departures, I can do a direct burn from Tylo to Kerbin orbital height for ~1,095 m/s. 

  Hide contents

 

However, manipulating this requires getting the phase angle right.  It takes 2 years + 110 - 230 days (roughly) for the return.  A Kerbal year being... um... errr... 426 days.  So, roughly 2.25 - 2.5 years to return.  Which means the phase angle needs to be in the right position for the trip.  I used this to get an idea where to have Tylo (and what side of Tylo) to figure out where to depart from it at, which is roughly 20-30 degrees just past prograde for Jool:

http://ksp.olex.biz/

It's doable, but you'd have to spend a bunch of time exploring maneuver nodes and departure dates.

I'm not even worried about getting an encounter with kerbin at this stage, i just want to find out how you ejected from the Jool system with a PE down to Kerbin's orbital radius on so little delta v.       Where was Tylo relative to Jool when you made your burn?     And what was the ejection angle from Tylo - in line with Tylo's orbit around Jool, was there an outward or inward component?

My best shot so far -

I get ejected from Tylo prograde to Jool's orbit, which raises my AP around Jool as much as possible.  Furthermore,  I waited till Tylo was on the night side of Jool, so our most distant point in the resulting jool orbit is facing the sun.    The second burn then ejects us from the Jool system on a heading retrograde to Jool's orbit around the sun, which should get us as low as possible.    

However, the first burn is 785 and the second about 760,  and that only lowers our PE to about halfway between the orbits of Duna and Dres.

[AeroGav]

ok,  I just got myself Precisenode mod which made it easier to play around.

It turns out, getting a low Kerbol PE after Jool ejection does depend on having your ejection from Tylo being prograde to Tylo's orbit around Jool, and of having your ejection from Jool being retrograde to Jool's orbit around Kerbol, so i was on the right lines.   However, I was missing a bunch of Oberth effect by splitting my burn.   By choosing the right burn date,  i can do it all in a single burn where my ejection angles from Tylo and Jool are more or less in line with one another and retrograde to the Kerbol orbit.

 

[WanderingKid]

17 minutes ago, AeroGav said:

ok,  I just got myself Precisenode mod which made it easier to play around.

It turns out, getting a low Kerbol PE after Jool ejection does depend on having your ejection from Tylo being prograde to Tylo's orbit around Jool, and of having your ejection from Jool being retrograde to Jool's orbit around Kerbol, so i was on the right lines.   However, I was missing a bunch of Oberth effect by splitting my burn.   By choosing the right burn date,  i can do it all in a single burn where my ejection angles from Tylo and Jool are more or less in line with one another and retrograde to the Kerbol orbit.

My findings were I was getting the best results dV wise when Tylo was about 30-35 degrees past Jool Prograde and when my burn point on Tylo was roughly 30 degrees after retrograde (both values in prograde orbits).  However, I wasn't coming in retro to Kerbin, that's very odd to me.