Landing on Laythe

[Rusty6899]

On career mode I decided to send an unmanned probe to get some science done around Jool. My plan for the mission was to encounter all of Jool's moons and do some science in the space above them before landing on Laythe.

Unfortunately, I approached Jool from the wrong angle and became stuck in a retrograde orbit. I had a fair bit of of fuel remaining, but nothing like enough to allow me to get into orbit around Laythe (5.2km/s of delta-v, ay right), as I was travelling in exactly the opposite direction to it. In the end, I encountered all the moons (except for Bop) and then got some extra science from a low Jool orbit.

Is there any advice on how to avoid this happening again? I don't use mods, so generally I just try to encounter a planet and then retroburn at the periapsis. I hadn't started exploring the moons of other planets until recently so it had never really mattered before about the inclination of a planetary orbit.

Edited November 20, 2013 by Rusty6899

[numerobis]

Laythe has an atmosphere, so you can jump right in no matter what your speed is.

But to your question: open up the settings.cfg and change the CONIC_DRAW_MODE (or whatever it is) to 0. Then when you set up the encounter with Jool, you can focus on Jool and see what your orbit will be relative to it when you get there.

[Smidge204]

If you time it JUUUUUUUUST right you shoujld be able to encounter Laythe on the trailing edge, like you would for a gravity assist, and use atmospheric braking and gravity assist to reverse your orbital direction and maybe even land. Basically gravity assist to completely reverse your orbit. This usually results in an encounter path that takes you into the surface but hey, you wanted to land anyway right?

As for advice on preventing it from happening again - always aim for the trailing side of the planet. use corrections while transferring between planets if necessary. You can double click on the target to center the view on it and zoom in to see how you're doing.

=Smidge=

[Rusty6899]

Yeh, I had considered trying to aerobrake, but I think I'll probably try to get a prograde orbit next time. I hadn't thought of focussing on Jool to see how I was approaching it, I'm pretty sure that will do the trick. Thanks.

[Kasuha]

Unfortunately, I approached Jool from the wrong angle and became stuck in a retrograde orbit.

...

Is there any advice on how to avoid this happening again?

Open your settings.cfg in notepad or another plain text editor and change the following parameters:

CONIC_PATCH_DRAW_MODE = 0

CONIC_PATCH_LIMIT = 6

Then, when planning a maneuver (and after you executed it) always check the destination if your approach trajectory is right. Note that the trajectory will be drawn around your destination, so you can focus on it by pressing Tab or by double clicking it. If the trajectory is not ok, execute a correction as soon as possible.

When switching SOIs, decrease your time warp as low as possible - x5 is best.

That's all you need to avoid that happening ever again.

[Geschosskopf]

Is there any advice on how to avoid this happening again? I don't use mods, so generally I just try to encounter a planet and then retroburn at the periapsis. I hadn't started exploring the moons of other planets until recently so it had never really mattered before about the inclination of a planetary orbit.

You just need to tweak your trajectory while en route to Jool so you go prograde around Jool. This usually requires 3-4 tweaks. The reaon is because the whole map view and the maneuver node system was designed only to get you from Kerbin to Mun, so it becomes increasingly difficult to use and less accurate in where it shows you'll even up the further from home you go. Jool is so far away from Kerbin that what you see for your encounter right after you leave Kerbin is not very close to what you'll have when you get out there if you do nothing.

The closer you get to Jool, the more accurate what you see on the map and the easier it becomes to fiddle with maneuver nodes on 1 side of the map while observing effects on the other. But the closer you are to Jool, the more these burns cost. This is why you should do several tweaks as you go along, so the last one won't cost very much. I usually do tweaks at each 1/4 of the trip. The purpose of them all is to narrow down my Jool Pe progressively until it's only like 200km. For the burns at 1/4 and 1/2way there, all I care about is Pe altitude, not inclination or whether I'm prograde or retrograde. The burn at 3/4 of the way sets the inclination and makes sure I'm going prograde, as well as puts the Pe no more than 500km out (the others having been satisfied with greater distances).

Final adjustment, however, cannot be done at all until you're in Jool's SOI. But this is so big that you can barely see Jool in the far distance when you get into it, so burns are still cheap. So this is where I put my Pe down to the top of the atmosphere, it already having been set on the right side of Jool and at the right inclination by the previous burn. But you're still so far away at this point that you can't set your final aerocapture Pe until you're much closer, like inside the orbit of Vall.

Anyway, keep an eye on your Jool Pe throughout the trip and keep it as low as you can. When you get close enough, make sure it's on the right side of Jool as you're looking at it and that your trajectory afterwards will be in the plane of the moons. Then finalize it with a couple more tweaks once in the SOI. I guarantee this will prevent you from ever going retrograde again unless you want to.

[Kasuha]

You just need to tweak your trajectory while en route to Jool so you go prograde around Jool. This usually requires 3-4 tweaks.

Okay. There are reasons for doing so many corrections if you want to hit something really small and desperately need to spend as little fuel as possible. Apart of that I don't see any reason to do more than one correction at about half of the interplanetary transfer and then one after entering Jool SOI.

The reaon is because the whole map view and the maneuver node system was designed only to get you from Kerbin to Mun, so it becomes increasingly difficult to use and less accurate in where it shows you'll even up the further from home you go. Jool is so far away from Kerbin that what you see for your encounter right after you leave Kerbin is not very close to what you'll have when you get out there if you do nothing.

I'm pretty sure the reason is very different. The wiggling is caused by physics engine causing small changes to the ship's center of mass and total velocity. The further the trajectory goes, the more pronounced these changes are.

As soon as you start at least x5 time warp the trajectory becomes rock solid and you can be 100% sure that it won't budge a single centimeter until you change SOIs (or go to x1 time warp again). And if you change SOIs at low time warp, the trajectory won't move by more than a few hundred meters. As long as the trajectory looks good, no corrections are necessary.

[Geschosskopf]

Okay. There are reasons for doing so many corrections if you want to hit something really small and desperately need to spend as little fuel as possible. Apart of that I don't see any reason to do more than one correction at about half of the interplanetary transfer and then one after entering Jool SOI.

It's always about spending as little fuel as possible because you never know how the plan might change. 3 minor tweaks along the way, each progressively improving your Pe, will only cost you maybe 40m/s in total. That will save you a lot over making 1 mid-course burn and then a rather significant burn at SOI.

I'm pretty sure the reason is very different. The wiggling is caused by physics engine causing small changes to the ship's center of mass and total velocity. The further the trajectory goes, the more pronounced these changes are.

As soon as you start at least x5 time warp the trajectory becomes rock solid and you can be 100% sure that it won't budge a single centimeter until you change SOIs (or go to x1 time warp again). And if you change SOIs at low time warp, the trajectory won't move by more than a few hundred meters. As long as the trajectory looks good, no corrections are necessary.

This isn't what happens to me. Even if I only have 1 ship in existence, and it's just going to Mun, I can't trust the map. On every single Mun trip I do, I leave Kerbin with a Mun Pe of 60k prograde and continuing on into a very wide Kerbin orbit if I do nothing at Pe. But about 1/2way to Mun, as I'm warping along at 500x or 1000x, suddenly the map changes to show me having a retrograde Pe right at the edge of Mun's SOI, after which I never even reach Mun's orbit but go into a tight ellipse back to Kerbin. And it stays showing this until about 30 minutes prior to where my original SOI change was, after which it jumps back to showing me something pretty close to what I had to start with (but never the same).

On long interplanetary flights, usually I don't have this happen but I still can't trust the map. While the Pe the map displays doesn't change during warp, apparently it changes in the background because it never remains where it was the last time I looked. Of course, my interplanetary missions always involve multiple ships so I'm always jumping around between them. Perhaps this is the root cause. But in any case, as stated, the map system wasn't designed to go anywhere further than Mun and has real and noticeable problems on longer trips.

[Kasuha]

On every single Mun trip I do, I leave Kerbin with a Mun Pe of 60k prograde and continuing on into a very wide Kerbin orbit if I do nothing at Pe. But about 1/2way to Mun, as I'm warping along at 500x or 1000x, suddenly the map changes to show me having a retrograde Pe right at the edge of Mun's SOI, after which I never even reach Mun's orbit but go into a tight ellipse back to Kerbin. And it stays showing this until about 30 minutes prior to where my original SOI change was, after which it jumps back to showing me something pretty close to what I had to start with (but never the same).

I know what you mean. It does not happen every time to me but it does happen every once in a while. It's some kind of bug in evaluating intersections of SOI with your trajectory. It is usually more likely to happen when your speed relative to the SOI is small. So far I know about four such bugs.

- bug with intersecting SOI at high speed which won't show you're intersecting it at all or will show you only part of the trajectory without PA

- bug which will draw you outside the SOI after you have crossed the point after which you should be inside

- bug which will draw you inside the SOI after you have crossed the point after which you should be outside

- bug which will draw the SOI exit point at the opposite end of the SOI if you're very close to the SOI's inside boundary

But it's nothing that can be fixed with corrections. All you can do is to fly along and hope the game will switch back.

[Geschosskopf]

I know what you mean. It does not happen every time to me but it does happen every once in a while. It's some kind of bug in evaluating intersections of SOI with your trajectory. It is usually more likely to happen when your speed relative to the SOI is small. So far I know about four such bugs.

I think I can now add another, now that I've got several ships flying back and forth between Jool's moons. Maybe it's because there are so many SOIs so close together there, and moving around each other. Anyway, what I'm seeing goes like this:

1. Start in orbit around any moon, take your pick.

2. Do a transfer to a different moon. Everything is fine as you set up the node, do the burn, and coast out towards the edge of the starting moon's SOI.

3. You leave the 1st moon's SOI and enter Jool's. Even if you cross the boundary at 1x warp, things immediately go haywire on the map. First, your entire future path disappears. All you have is the blue current orbit and instead of heading off at a tangent from the 1st moon, it's in a tight curve around it for about 3/4 of a circle, where it just comes to an abrupt end.

4. Cross your fingers and wait a minute or so. Eventually, this weird 3/4 orbit of the starting moon disappears and is replaced by something resembling what you had when you finished the burn. However, you only see this in flickers because it's alternating with something entirely different about 6 times per second. The path you see in the other flickers usually has you taking as sharp turn down towards Jool and then being shot out of the system.

5. This flickering of different paths continues for pretty much the entire 1st 1/2 of the trip to the target moon. Then it settles down showing you heading towards your destination as planned. HOWEVER, your Pe at the target is WAY different from what it was at the end of your burn, before you left the 1st moon's SOI. It's usually moved 500-600ikm. It thus takes a pretty good tweak or 2 in the latter 1/2 of the trip to get your Pe back where you wanted it.

I had another weird thing happen a while back, too. After a final tweak about 7/8 of the way to Duna one time, the map showed I'd have a prograde Pe of about 60km with the SOI change due in about 18 hours. But what I got was a 1.2Mm retrograde encounter quite a few hours before my expected SOI change. And I had to act fast on this because I was at the VERY edge of Duna's SOI, only being in it for like 10 minutes. Unlike the map being weird, this was the ship itself being weird, so I couldn't trust that everything would sort itself out if I did nothing. Therefore, I suddenly had to do an unexpected 1000+m/s burn to flip the orbit over and get my Pe down next to Duna. Very annoying.

[Rusty6899]

That's all really helpful. I had always wondered about the flickering/changing Pe markers but I had just decided to accept them as part of the game. I'm guessing it will help a lot to do corrections mid way. One of the things I like most about the game is that there are so many different areas to perfect. I thought I nearly had the game sussed when I first landed on Duna, but that's really just the start of it.