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Jool Transfer Predicament

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Snark

Snark

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How much Jool-relative velocity do you have?

What's your ship's TWR?

Does it have a heatshield?

Parachutes?

Wings, airbrakes, other aero surfaces?

Mass?

1.6 km/s is a pretty meager budget for entering Jool system. If you can aerobrake, that would help a lot. Jool itself is notoriously unfriendly for aerobraking in 1.04, but Laythe may be an option, depending on your speed and your ship design. Can you give more details about your ship?

Option 1, land on Laythe. Adjust course for Laythe intercept long before entering Jool system, this will take trivial amounts of dV. Just before hitting Laythe atmosphere, retro-burn all of your fuel, both to soften the aerobraking blow and to lighten the load. Aerocapture, then land with parachutes. Or if you don't have chutes, save a little fuel for slowing down to a safe speed just before landing.

This option assumes your ship is tough enough to handle aerobraking, and either has chutes or else enough TWR to do a powered landing on Laythe.

Option 2. While still well outside Jool's SoI, adjust Jool periapsis down to just above atmosphere. Right at periapsis, do a big retro-burn to capture to Jool. Hope you have enough dV to lower your Ap down to a Pol or Bop intercept.

This option assumes that your Jool-relative velocity is low enough for 1600 m/s to achieve capture.

Option 3. Reverse Tylo slingshot. Similar to option 2, but instead of low Jool periapsis, you set up a low Tylo periapsis, on the LEADING side of Tylo. Periapsis should be as toe-scorchingly low as you can manage without lithobraking. This takes advantage of Tylo's orbital motion to slow you down, in addition to getting Oberth effect from the burn at low periapsis.

The elephant in the room here, no matter what you try, is how fast you're moving relative to Jool when you enter its SoI. If you're coming screaming in like a bat out of hell, you'll probably be limited to just doing a flyby.

Edited by Snark
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SpaceplaneAddict

SpaceplaneAddict

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2.4 TWR currently

No heatshield or parachutes.

For atmo bodies I was intending to use an SSTO I have docked to my ship...

The whole craft was to land on Non-Atmo bodies.

http://forum.kerbalspaceprogram.com/threads/136781-Jool-5-YAY%21 is my mission report thread. The second page has pics and info of my current mission.

-SPAddict

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Starhawk

Starhawk

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Tylo gravity assist. Make a maneuver node an hour out or so. Then focus in on Jool, and play with the maneuver using the smallest possible adjustments. A Tylo gravity assist can put you into Jool orbit with very little delta-v expended.

You want to make sure your CONIC_PATCH_LIMIT is set to at least 4 or 5. This is a value in the settings.cfg file. This will allow you to see your trajectory across several SOI changes.

Good luck.

Happy landings!

ETA: Laythe is the only body in the Jool system which has atmosphere. Except for Jool itself.

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Starhawk

Starhawk

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I knew that :D

The reason I brought a whole SSTO spaceplane was more for aesthetics than practicality.

No worries. As you've seen, I brought a whole spaceplane all the way to Jool, myself, and it's only for use as the lander at Laythe. :)

Happy landings!

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Snark

Snark

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I knew that :D

The reason I brought a whole SSTO spaceplane was more for aesthetics than practicality.

OK, the fact that you have a spaceplane can work for you, since wings make pretty good aerobrakes.

A direct hit on Laythe would probably fry you, but you can use a Tylo gravity assist (spending most of your dV there) to capture to Jool orbit that touches Laythe's, then use minor amounts of dV to set up a Laythe intercept. Then use the spaceplane to aerobrake and land on Laythe. The challenge on Laythe will be finding terra firma to land on, can your plane cruise a reasonable distance?

Edited by Snark
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SpaceplaneAddict

SpaceplaneAddict

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OK, the fact that you have a spaceplane can work for you, since wings make pretty good aerobrakes.

A direct hit on Laythe would probably fry you, but you can use a Tylo gravity assist (spending most of your dV there) to capture to Jool orbit that touches Laythe's, then use minor amounts of dV to set up a Laythe intercept. Then use the spaceplane to aerobrake and land on Laythe. The challenge on Laythe will be finding terra firma to land on, can your plane cruise a reasonable distance?

Nope.exe

Seriously, my SSTO can only go so far... I don't have extra jet fuel to supply it.

Feeling desperate now... I don't have a clue as to "gravity assist"

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RocketPropelledGiraffe

RocketPropelledGiraffe

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Gravity assists in the Jool system are so much fun, try it!

Make sure you have set CONIC_PATCH_LIMIT to 4-5, as StarHawk indicated. Just edit the value in the settings.cfg file with a text editor (backup first, if you are unsure!)

Now just play around with the maneuver tool a bit, you do not have to actually do a burn to get the idea:

Set a maneuver node close to your current location and focus on Jool. Try to set the maneuver as a close flyby around Jool and to get an encounter with Tylo, Laythe, or Vall immediately afterwards. In my experience there will usually be at least one of the inner moons set up to get an encounter without too much fiddeling.

The trajectory after the moon encounter will show you how you will fly on after flying by the moon and getting back in Jool's SOI. Now play around a little bit (gently!) with your maneuver to experiment and see what happens:

If your moon flyby is on the leading side, you will be slowed by the moon's gravity and, ideally, get into an elliptical but stable orbit around Jool. If your flyby is on the other side, the moon's gravity will increase your velocity and eject you from the Jool system.

You will see that with very small adjustments to the maneuver you will get a huge change in your possible final Jool orbit.

Edited by RocketPropelledGiraffe
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Starhawk

Starhawk

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Nope.exe

Seriously, my SSTO can only go so far... I don't have extra jet fuel to supply it.

Feeling desperate now... I don't have a clue as to "gravity assist"

May I point you in the direction of the Drawing Board in the Tutorials subsection to start?

OK, I checked the Drawing Board and there's this tutorial and there's also this one.

I haven't checked out the tutorials, but I expect them to be very informative.

The basic concept of a gravity assist is that you can use a body's gravity to alter your trajectory. If you enter Tylo's SOI going in one direction, but leave going in a very different direction, you will change the resulting orbit around Jool very significantly. By setting up a maneuver node near your ship while you are in interplanetary space, you can adjust your trajectory until it interacts with Tylo (or Laythe, or even Vall). Then you can adjust the maneuver node in very fine increments to change how near you get to Tylo's surface and on which side you will pass.

You will need to change the CONIC_PATCH_LIMIT setting I mentioned in your settings.cfg. As pointed out above, that's just a text file you can edit (with something like Notepad if you run windoze).

Give it a try. Hope this helps.

Happy landings!

Edited by Starhawk
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Red Iron Crown

Red Iron Crown

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A direct hit on Laythe would probably fry you, but you can use a Tylo gravity assist (spending most of your dV there) to capture to Jool orbit that touches Laythe's, then use minor amounts of dV to set up a Laythe intercept. Then use the spaceplane to aerobrake and land on Laythe. The challenge on Laythe will be finding terra firma to land on, can your plane cruise a reasonable distance?

This is the best play.

hKwUrdH.png
Yeah, I get the feeling that will be my last shot. Not sure if I can land on Pol, I got an accidental encounter. Anyone tell me "how" to set up the Tylo encounter?

It is very tricky to do without a node editor like PreciseNode or MechJeb, as tiny changes in the transfer trajectory have large effects. Best thing to do is make your correction after leaving Kerbin's SoI, target Tylo and get your Jool path running close to parallel to Tylo on the "right" side of Jool. The use very small adjustments pro/retro and rad+/- to refine your encounter time to get an intercept with Tylo. Then you can further tune what Tylo does with your ship when it passes through its SoI.

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Warzouz

Warzouz

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Yeah, I get the feeling that will be my last shot. Not sure if I can land on Pol, I got an accidental encounter. Anyone tell me "how" to set up the Tylo encounter?

Pol is orbiting slowly around Jool, so you may need more dV to go directly there. I usually do a Pol refuelling but I've enough fuel for that brake. You must tweak your manoeuvre node to encounter Tylo (it's much easier than encounter Pol...).

I would do it that way (but I'm not an expert...) :

- If planes are too different, try to align to cross Tylo orbital plane in a flattest angle (it's the same as Laythe and Vall)

- Then try to find Tylo encounter buy tweaking the node.

- Set your trajectory to cross Tylo SOI in _front_ of it (so you'll be slowed). Get a 10km PE to Tylo.

- Check you resulting orbit, you may tweak to get descent inclination.

- If you need to slowdown, the Tylo PE is the best location. You can evaluate this burn by setting it in advance.

- Try to get you resulting orbit up to Pol.

Of course you must avoid ending in a retrograde orbit around Jool

PS : even if set, I suggest you recheck projected orbits when entering Jool SOI, then when entering Tylo SOI.

"Precise node" mod help quite a lot with node tweaking. MJ also has a "node editor" to do the same.

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Starhawk

Starhawk

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That's perfect! You can set up a maneuver node at your apoapsis and tweak your encounter with Tylo to adjust your orbit some more. Hopefully, you can get the Laythe encounter you originally wanted. You can also use the Tylo gravity assist to improve your inclination if needed.

1.3 km/s should be plenty to get you captured around one of the inner moons as long as you use another gravity assist.

Still wishing you those...

Happy landings!

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celem

celem

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Yeah as the guys illustrated above (and you seem to have achieved on your way in) Tylo is free-dV. In both directions, you can always either speed up or slow down at a flyby.

I suspect you can find a solution for Laythe too, spend most of your dV at this next grav assist to make use of Tylo's rather reasonable Oberth effect, even if you cant get a direct Laythe encounter then an encounter with any of the other inner bodies should provide opportunity for yet another free course change and shot at laythe aerocap.

Multi-moon bodies are awesome, you can pinball round the Jovian System on a shoestring budget if you have time and patience.

I definately second the recommendation further up-thread about a mod like PreciseNode, this is a pretty brutal task on stock nodes.

Edited by celem
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Starhawk

Starhawk

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OK. Try this. Make a maneuver node a few minutes away from your current position. Give it -5.3 prograde, 72.5 normal, and -18 radial. That should set you up with your ascending node out at your apoapsis, and a Jool periapsis of 530 km or so. Then a burn out at your apo to correct your inclination should cost under 100 m/s. You could then try for an encounter with Laythe or another assist to get you the Laythe encounter.

OTOH you could try this. A tiny burn a few minutes from your position of about -0.2 m/s prograde will put your periapsis at Tylo outside the surface. You could burn at Tylo periapsis to capture in Tylo orbit for about 455 m/s or so. That would leave you in a very elliptical Tylo orbit, however.

Or this. Set up a node a few minutes from your current position with 9.5 normal and -5 radial. That should give you a periapsis with Tylo that is above the surface and a good inclination for your Jool orbit. A burn at Tylo's periapsis of about 172 m/s retrograde will give you a Jool periapsis which is above the atmosphere.

There are options.

Happy landings!

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