Where should I put my Mun encounter point

[KrisKelvin]

When I create a maneuver node to get to Mun, I first pull on the prograde handle to get the apoapsis height up to the Munar orbit height, then I rotate the node until I get an encounter (which I think is the little brown circle with the hooked arrow in). But as you see from this video, there is a range of angles which will give me an encounter. As I rotate the node, the Munar encounter point moves around (plus a whole load of extra coloured lines annoyingly appear to confuse me!).

So my question is, where should I be trying to get my Munar encounter point to be? Or in other words, when should I stop rotating the node? Where is the right place?

https://drive.google.com/file/d/1stmRJmbL-KK0zoAa4bwhPNy-ikkMS3i4/view?usp=sharing

Edited June 27, 2020 by KrisKelvin

[Streetwind]

Your goal should be to get the lowest periapsis over the Mun possible without crashing into it. For example, 10km or so. Reason being that capture burns are more efficient the lower the flyby periapsis is.

You will discover that you best achieve this through a combination of adding dV and repositioning the maneuver node. For precision control, I recommend using the node editor in the lower left instead of dragging the node around with your mouse. After you have your initial encounter, focus your view on the Mun to tweak it.

Edited June 27, 2020 by Streetwind

[KrisKelvin]

7 minutes ago, Streetwind said:

Your goal should be to get the lowest periapsis over the Mun possible without crashing into it. For example, 10km or so. Reason being that capture burns are more efficient the lower the flyby periapsis is.

You will discover that you best achieve this through a combination of adding dV and repositioning the maneuver node. For precision control, I recommend using the node editor in the lower left instead of dragging the node around with your mouse. After you have your initial encounter, focus your view on the Mun to tweak it.

Oh is that what the purple line is? Right.. I'll try that.

Edited June 27, 2020 by KrisKelvin

[Streetwind]

53 minutes ago, KrisKelvin said:

Oh is that what the purple line is? Right.. I'll try that.

Yes, your predicted orbit line changes color when transitioning a sphere of influence boundary. Normally it's yellow-brown. After the first transition it becomes purple. After the second, green. After the third, red. And so on. Typically, green is the most you'll see, because the pre-plotting cuts off after the third "patch", but you can increase this in the settings.

I went and made a video to show you how I make a maneuver node for the Mun. Because I've done this probably a thousand times, it goes pretty quickly But here, I'll walk you through it step by step:

1.) Zoom out and get a nice top-down view.
2.) Set the Mun as your target.
3.) Align the view so that the Mun is roughly "12 minutes past the full hour", if the circle of its orbit was a clock face. You can see me move the mouse to indicate the angle.
4.) Make a maneuver node on the bottom of Kerbin.
5.) Add prograde dV until you have a Mun encounter. You can drag the handle for this, but I just happen to have memorized that a typical Mun transfer costs around 840 - 850 m/s worth of dV, so I just wrote 840 into the node editor. Because I guessed the angle well in step 3, I got an instant encounter.
6.) Focus your view on the Mun. Find a nice zoom setting, and shift the camera so you can see Kerbin. You'll have to click the maneuver node to resume editing, and sometimes this can be tricky if it is buried in a heap of other clickable things.
7.) Click the periapsis to pin the display of its altitude.
8.) Use the arrows in the middle of the editor gizmo to move the maneuver node in such a way that the periapsis gets closer to the Mun.
9.) If at some point this stops having any effect, or even starts moving the periapsis away again, then start adding a little prograde dV again.
10.) Keep using the movement arrows and the prograde/retrograde dV handles until you have a roughly 10km periapsis. You'll see me use the slider on the right side of the maneuver editor near the end; that controls how precise the inputs are.

Should you get into a situation where your trajectory disappears into the Mun, you've added more dV than necessary. Remove some with the retrograde handle.

Edited June 27, 2020 by Streetwind

[KrisKelvin]

wow! that's great. Learned all sorts of things there (like you can type a delta V into the maneuver gizmo! and that you can switch focus to Mun). Thanks. I do find it annoying that KSP doesn't just have a pan feature like most games do. The view always has to be centred on something, so it can be really annoying to get the view you need.

One question.. what does set Mun as target add to the process? I've not used that before, I just use the maneuver node. All set Mun as target seems to do is draw a yellow diameter across your orbit for some reason. How does that help?

[RoninFrog]

16 minutes ago, KrisKelvin said:

wow! that's great. Learned all sorts of things there (like you can type a delta V into the maneuver gizmo! and that you can switch focus to Mun). Thanks. I do find it annoying that KSP doesn't just have a pan feature like most games do. The view always has to be centred on something, so it can be really annoying to get the view you need.

One question.. what does set Mun as target add to the process? I've not used that before, I just use the maneuver node. All set Mun as target seems to do is draw a yellow diameter across your orbit for some reason. How does that help?

Setting something as target will show by how much you miss if your maneuver node doesn't get an encounter.  It doesn't really help a lot for the Mun since the Mun is so big and close, but it is useful for Minmus and essential for interplanetary transfers.

 

Also, you can sort of pan the camera by right clicking on a part and clicking "Aim Camera".

Edited June 27, 2020 by RoninFrog

[KrisKelvin]

43 minutes ago, RoninFrog said:

Setting something as target will show by how much you miss if your maneuver node doesn't get an encounter. 

How so?

[jimmymcgoochie]

10 minutes ago, KrisKelvin said:

How so?

Little blue arrows should appear on your orbit and the orbit of your target indicating where the two will be at the closest approach, and the arrow on your orbit will also tell you the distance from the target, relative velocity and when it will happen.

You may have to switch on 'always show closest approach' for this to work properly, it's in the main menu settings and is well worth switching on as it's very helpful and (AFAIK) doesn't impact on game performance.

Transfers to the Mun are pretty easy to judge- if you're pointing prograde and the Mun is directly ahead of you, that's the point when you make your burn- a transfer to the Mun takes a day and the Mun orbits Kerbin every 4 days. It's a good approximation and can help you get the rough encounter so you can then tweak it to be more efficient.

[KrisKelvin]

1 minute ago, jimmymcgoochie said:

Little blue arrows should appear on your orbit and the orbit of your target indicating where the two will be at the closest approach, and the arrow on your orbit will also tell you the distance from the target, relative velocity and when it will happen.

You may have to switch on 'always show closest approach' for this to work properly, it's in the main menu settings and is well worth switching on as it's very helpful and (AFAIK) doesn't impact on game performance.

Transfers to the Mun are pretty easy to judge- if you're pointing prograde and the Mun is directly ahead of you, that's the point when you make your burn- a transfer to the Mun takes a day and the Mun orbits Kerbin every 4 days. It's a good approximation and can help you get the rough encounter so you can then tweak it to be more efficient.

ok, I'll give that a try. Thanks