Maneuver node to the Mun

[fastbikkel]

When making a maneuver node to the mun, one gets the icons with the arrows.

Indicating a front pass, or a rear pass.

But is that really what the arrows represent?

I have made a trajectory to pass in front of the mun, just like the real Apollo mission.

However, when arriving in the SOI of the mun, i noticed i was arriving too late and passed around the back. I could still go to orbit, but it was not what i had planned.

Now i have learned to compensate and not count on the icons, but should i be able to trust them?

For now i just put my trajectory waaaay in front of the mun, sometimes even so far that the icon just disappears.

In short, i use my own eyes for this and hope for the best, making mid course corrections.

[Kasuha]

I don't think there are any icons that show you "front pass" or "rear pass". Of course you can read it from the trajectory itself.

When changing SOI you should take care to not cross the boundary at any significant time warp level or your resulting trajectory after the crossing may get changed. That's especially important if you're setting up near misses (low periapsis, gravity slingshot etc). The lower time warp level you use the better your planned trajectory is preserved.

Edit: Regarding the icons, I wonder what you're actually referring to. Picture might help, probably. Or you can check the Wiki for explanation of icons used in the game.

http://wiki.kerbalspaceprogram.com/wiki/Maneuver_node

Edited February 5, 2014 by Kasuha

[Dirty Bob]

The only thing I ever see with the maneuver nodes changing from one to the other is from the angle at which you're viewing it. The icons will change their relative location as you rotate the camera around them.

[TechnicalK3rbal]

Those "arrows" are the periapsis or inclination nodes. Move the mouse over it to see how low you're going to be, (periapsis) or the inclination (it'll say AN or DN) to see your relative inclination.

[fastbikkel]

I don't think there are any icons that show you "front pass" or "rear pass". Of course you can read it from the trajectory itself.

I have to think a couple of times about what that means. I have not read anything from the trajectory itself in regard to where i will end up around my target (mun in this case).

There is no way i can think of, yet, that will help me make a good aim. For now it seems just luck, combined with the fact that the mun is close so there is a real good chance i will make it.

I have made it all the time, making manual corrections.

I will definately look at the wiki link though, hope that will make it more clear.

Thanks.

@TechnicalK3rbal

I cannot remember seeing something popup when i hover the mouse over that arrow, but i will surely try again when i start KSP again soon.

Thanks to all.

[fastbikkel]

@kasuha

I have just opened that wiki link, it was the one i read initially, this has helped me a lot yes.

But .. i do not see the info there that explains what i asked here about those arrows and how to navigate to the mun.

I guess that is on another wiki page. I find it hard sometimes to define what i want to know, so searching on the web gives mixed results. Hence my question here.

[Serratus]

First, in what mode is your patched conics operating? Second the planned trajectories are always just a little bit off from reality due to the fat that system practically guesses the end result. Third - there are no nodes that tell You which way will you pass any celestial body since directions in space are completely different and subjective.

Maybe You could provide pictures? That would help understand what You're saying.

EDIT: I just realised You were talking about encounter nodes - they however do NOT indicate if You pass in front or behind the target. They just indicate first and second closest approach. To know which way will you pass a body You need to directly look at Your trajectory and on which side of the body it is.

Edited February 6, 2014 by Serratus

[Kasuha]

Arrows on the trajectory show apoapsis and periapsis, inclination, closest approach and crossing points. If you put your mouse over the marker it will tell you the type and some numbers about it.

Apoapsis and periapsis tell you which point on your current/planned trajectory is closest to/furthest from the planet/moon

Inclination markers tell you how much is your trajectory inclined compared to target trajectory and around which axis

closest approach points show you where on your trajectory you will be the closest to your target and where the target will be at that moment

Crossing points show you where your trajectory crosses the target trajectory (or passes sufficiently close) and where your target will be when you'll be at that crossing.

Maybe you could try some of available video tutorials on YouTube where they explain things in context.

Perhaps this one might help you?

[KerbMav]

Your predicted path will show you if you pass infront or behind the moon, if you are unsure about the direction you are going in you can look at the times at which you will arrive on the different markers.

Actually getting your craft on the exact same path you planned with your maneuver node is not that easy.

1. You will have to split your burn time to before and after you arrive at the node.

(e.g. for a 1 minute burn, start 30 seconds before you arrive at the node)

2. The predicted time needed for the burn is not always exact.

3. Burning more/less then needed is not unusual - better to not watch the beauty of the craft burning in the last phases of the burn, but watching your orbit in map mode, throttling back.

4. Adjustments/course corrections may still be needed though.

[fastbikkel]

Your predicted path will show you if you pass infront or behind the moon,...

This is exactly what i assumed, but some others here do not seem to agree.

Thanks all though, it is still a learning process for me. The maneuver nodes are very comfortable to me now, but that last thing with the arrows were a big questionmark for me.

@kasuha

I will look at that youtube movie, thanks for mentioning.

[fastbikkel]

....

EDIT: I just realised You were talking about encounter nodes - they however do NOT indicate if You pass in front or behind the target. They just indicate first and second closest approach. To know which way will you pass a body You need to directly look at Your trajectory and on which side of the body it is.

If that is the case, it seems pure guessing to make a correct approach. Because i cannot determine how quick the mun will arrive on my designated arrivalpoint.

I can accept any answer, i will just deal with it.

I will try and make a screenshot to clarify my situation.

Still, i can reach the mun, i just wanted to realise what is going on exactly. Eventually i want to reach out to the other planets and it would help me to understand the basics.

I do realise that other planets further away need other ways to prepare. I found a nice website with a plannertool for that, from one of Scott Manley's movies.

[Serratus]

The simplest way I can think of for Your problem would go like this:

1. Get an encounter

2. use 'Tab' in map mode to switch camera to looking at Mun

3. Figure out if predicted path is what You want

4. If You are not going into the path You want then turn on RCS and delicately experiment thrusting with it in different directions while still closely looking at that path in map mode

5. You should be able to move an entire trajectory with minuscule amounts of RCS fuel

Keep in mind that this only works if You are still close to Kerbin! The closer You are to Your target, the more dV You would need to make such course correction. For IP missions You would do well to include mid-course-correction about 2/3 of the way there because path error grows with distance so it wouldn't be practical to try and get perfect encounter while still in Kerbin SOI. But as I said - for transfers to the Mun and Minimus the above plan works great.

Make sure You have Patched Conics set to 0 mode! You can do this in settings.cfg or in MechJebs "Maneuver Node Editor" tool. I hope my explanation makes sense Cause I got turned-around a bit by myself

[Claw]

Maybe I'm remembering wrong (since I'm not at my computer atm), but don't you get a little ghost Mun when you hover the mouse between the encounter nodes? Maybe that's just when you're doing the initial injection burn.

EDIT: Now that I think about it, I think the ghost appears when playing with maneuver nodes.

Edited February 6, 2014 by Claw

[fastbikkel]

I will have to look in KSP soon to try again, hope i have time tonight and that KSP will not crash for a change.

This game/sim gives me nice adrenaline shots whenever i achieve something, hope to land on the mun this weekend.

My apollo style rocket is done, i am in the final stages of testing.

[Claw]

I finally broke down and removed all mods except MechJeb and Engineer (for designing). I have a lot fewer crashes now.

[fastbikkel]

I think some people here did not understand what i meant. I meant the left or right arrow that are at the planet icon when you adjust the maneuver node towards the mun.

Now i see the confusion here. Some thought i meant the little arrow icons for periapsis and apoapsis, but that is not what i meant at all.

If you make a maneuver node and drag the prograde icon, the trajectory will expand to a point where an icon will pop up with a planet and a curved arrow around it, either left or right.

Usually when i drag the prograde icon, first the front pass arrow appears, then when you drag the prograde even more, a rear pass arrow appears.

Now i made a front pass trajectory, but i passed way around the back. In effect, i really should not pay attention to those arrows because they have been wrong all the time or... i just do not get it.

I will start KSP now and try and make screenies.

@Claw

I only have an alignment indicator installed, but even before i installed it, KSP crashes every 20 minutes or so. BUt that is a different topic :-)

[Claw]

Now you're making me think of the orbital trajectory that pops up when your maneuver node orbit crosses an SOI. Is this a fairly large arrow? I'm also starting to wonder what we all mean by "front" and "behind."

Looking forward to your pictures. You have made me very curious.

Edited February 6, 2014 by Claw

[fastbikkel]

Let me find a website to host my picture, i dont seem to be able to just upload it here.

I have read the words "mun encounter" and "mun escape", respectively they look like front and rear pass.

[fastbikkel]

Here it is, i think.

[Serratus]

Ok, I see. The thing is - the direction of that line on the icon doesn't mean anything. Problem solved.

[WhiteKnuckle]

Here it is, i think.

http://i1306.photobucket.com/albums/s570/stefanvvvv/example-ksp1_zps2f6924b6.jpg

Yeah the points you highlighted don't mean anything.

When you get to the purple periapsis marker, the mun will be where the ghosted purple sphere is. So in this case you'll be coming in behind the mun, you can adjust your maneuver node till the line of your flight path is in front of the ghost mun icon.

[Kerba Fett]

Since I don't think anyone else has said this, the green sticks on the maneuver node represent prograde and retrograde.

The blue sticks are for radial + and - ( to alter your path left or right)

The purple sticks are for normal + and - ( to alter your path for climbing or descending)

To get to the Mun place a node on your orbit where the Mun lines up with the horizon of Kerbin. Drag the prograde stick (the one without the x in the end) till your projected path shows a Mun encounter. There should now be a periapsis marker in the purple segment of the projected path. Adjust prograde/ retrograde to get the PE marker where you want it. (front or back pass)

You can also adjust radial a but to reshape your path. Zoom the camera out in the map view and swing it over so you can see the Mun in the foreground for fine tuning.

Then just point your navball at the blue node marker and burn when the count reaches zero. Recheck your course after the burn incase you need to do a minor correction then just wait for the encounter.

[Yasmy]

First, the arrows you were talking about are sphere of influence change indicators.

They appear at the end of a trajectory within one sphere. Note the color of the indicator

is the color of the trajectory your are leaving.

The easiest way to tell which way you are going to orbit after an encounter is change the conics mode to 0. The default mode is 3. Mods such as Enhanced Maneuver Node or PreciseNode (shown in the images below) allow you to change your conics draw mode without editing your config file.

But if you are averse to mods, in your setting.cfg file in your KSP directory, just change

CONIC_PATCH_DRAW_MODE = 3

to

CONIC_PATCH_DRAW_MODE = 0.

Javascript is disabled. View full album

The first two images are the same encounter, but with conics mode changed from 3 to 0.

In the second image you see the encounter relative to the moon, instead of relative to Kerbin.

This way you can see the spacecraft will orbit the Mun counter-clockwise.

Images three and four show an encounter that puts you into a clockwise orbit of the Mun (seen from above).

Check out the purple trajectory around the Mun in image 4.

Edited February 7, 2014 by Yasmy

[Yasmy]

Now the reason things look different from Kerbin then they really are when you show up at the Mun is simply because the Mun is moving faster than you are on its orbit. Suppose you show up on the near side of the Mun. While you are busy inserting yourself into a Munar orbit, the Mun is still moving around Kerbin faster than you are. Thus you end up losing ground and orbiting the Mun eastward (counter-clockwise from above).

Edited February 7, 2014 by Yasmy

[fastbikkel]

Thanks again guys for all the answers.

SO these arrows do not mean anything, well at least i was thinking that before. I was relying on them without good reason.

I must admit i have to re-read some comments here again to fully understand what it means. The whole "conics" thing is something i clearly do not get, i will have to put time in this.

I will edit the values in the CFG file to get a feel for it.