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Mun rendezvous issue


Garthog
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I'm a newbie in career mode and have hit a roadblock in attempting to fly by and gather scientific data near the Mun - I've followed Scott Manley's tutorials on how to do this, but I'm doing something stupid because I can't succeed - after achieving a stable orbit around Kerwin, I place a manuever node 90 degrees ahead of my target (Mun) - no matter how I try, I cannot get a projected orbit to get closer to the Mun than 2429.6 km - no matter how many ways I try to do it (ahead of it, behind it, near it), the closest approach miraculously stops at 2429.6 km - also, the application is so sensitive as I increase the projected orbit near the Mun that I instantly "pop" into a totally different orbital arrangement (is that the effect of the Mun's sphere of influence?), but still keeps me 2429.6 km away from it - and finally, is there a way to zoom in on the projected near encounter of the Mun in map view?  Mine remains centered on my spacecraft and when I try to zoom in the "spaghetti" of orbits near the Mun I only zoom in on my spacecraft so it is impossible to analyze what my projected path(s) are doing very easily.  Sorry for all the questions - I love the application but I'm up against a "wall" that's preventing me from advancing - the issues are exactly the same in sandbox as well as career mode.  Thanks in advance for anyone's assistance/suggestions.

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Hello, and welcome to the forums!  :)

2 hours ago, Garthog said:

I place a manuever node 90 degrees ahead of my target (Mun) - no matter how I try, I cannot get a projected orbit to get closer to the Mun than 2429.6 km - no matter how many ways I try to do it (ahead of it, behind it, near it), the closest approach miraculously stops at 2429.6 km - also, the application is so sensitive as I increase the projected orbit near the Mun that I instantly "pop" into a totally different orbital arrangement (is that the effect of the Mun's sphere of influence?)

I have to guess what you mean by the "popping" thing, since you didn't include a screenshot, but do you mean that your projected path changes from a simple ellipse around Kerbin in one color, to a multi-colored thing that changes at a couple of points up near the Mun's orbit?  If so, that's good-- it means your projected path will be hitting the Mun's SoI, which is exactly what you want.  :)

Here's the easy way to get a Mun encounter:

  1. Get into low circular orbit around Kerbin (a.k.a. "LKO" as it's usually called in the forum).
  2. Drop a maneuver node (doesn't matter where) and drag the prograde handle until your Ap is up by the Mun's orbit.
  3. Now grab the middle of the node (not one of the handles) and drag it-- this lets you drag the node along your orbit.  Drag it around until you see that your projected path hits the Mun's SoI.  There's your encounter, right there!
  4. A marker will appear showing your periapsis around the Mun.  You want the lowest Pe you can get over the Mun.  You can do that by a combination of tweaking the maneuver node's prograde/retrograde amount, and sliding the maneuver node back and forth a little along your LKO path.
2 hours ago, Garthog said:

is there a way to zoom in on the projected near encounter of the Mun in map view?  Mine remains centered on my spacecraft and when I try to zoom in the "spaghetti" of orbits near the Mun I only zoom in on my spacecraft so it is impossible to analyze what my projected path(s) are doing very easily.

You can change the focus in the map view so that it's focused on the Mun instead of your ship.  Just double-click on the Mun.

The nice thing is that when you do this, the orbital display will show you your projected path as it goes past the Mun, relative to the Mun, which is exactly what you want.

While it's focused there, you can even adjust your flyby path, if you rotate the camera until your LKO maneuver node is visible.

Once you're done, hit the backspace key to return focus to your ship.

2 hours ago, Garthog said:

Sorry for all the questions - I love the application but I'm up against a "wall" that's preventing me from advancing - the issues are exactly the same in sandbox as well as career mode.

Not at all-- that's what this forum is here for!  :)

 

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Oh the joys and wonders of being a novice space explorer. Those were the good old days.

 

Anyway, here’s an alternate method I always used: Get into a circular LKO and time warp in staging view (i.e. not map view) and wait until the Mun rises over the horizon. As soon as it does (you can be off by a bit, don't worry about being exactly accurate), stop time warp and start burning prograde. While you burn, switch to map view, pull up your navball (so you can continue controlling your craft with the keyboard), and watch your orbit rise until it hits the Mun’s orbit, then cut your throttle. If you did it right, you should have an encounter. As mentioned, you'll know there's an encounter because a bunch of new orbit line will appear, plus you'll have a small marker in the shape of a circle with an arrow, which will be labeled as 'Mun Encounter' when you mouse over it.

 

At this point you can tweak your encounter to be more accurate by focusing your view on the Mun. While in map view, double click it, or single click it and select ‘Focus View’. As mentioned above, this show what your trajectory relative to the Mun will be during the encounter. Once you’re focusing on the moon (still in map view), use your Navball markers to give yourself very tiny nudges in one direction or the other until you find the direction(s) which will bring you closer. This is not the most efficient way to fine tune your approach but it does wonders in terms of giving you a real understanding on how burning in different directions will move your orbit.

 

The most efficient way to correct your course is to do a mid-course burn (about half way out to the Mun encounter, again you can be a bit off it doesn’t need to be exactly half way) assisted by a maneuver node so that you can combine different directions of burning in a single maneuver.

 

Make sure your approach is at least a few Km high over the Mun’s surface, otherwise you will find yourself crashing into its mountains.

 

Hope this helps and feel free to ask more!

Edited by A_name
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One thing you said that hasn't been addressed:

Sadly, the "Close Approach Marker" (when you are setting a maneuver node) cannot be completely trusted.

It tries its best to pick a spot on your current orbit, in your current SOI, where you should be at one of the 8 theoretical closest approaches. So what it ends up giving you is a ballpark estimate that you can use to figure out how to get closer than you are now.

HOWEVER, once you actually have an encounter that changes your SOI -- the marker does not work anymore.

Once you get that spaghetti mix of orbits suddenly showing up (that indicate you're going to get an encounter with something!) you have to start looking for a Pe marker instead. That shows your real closest approach.

 

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Also, an alternate way to focus maneuver nodes and celestial bodies ... just tab over to them!  This also allows your maneuver node to stay open.  Backspace (or tilde as the case may be) still works to return focus to the craft.  This also allows some trickery when you want to intercept a contract orbit, because you can drop a node on a near encounter, look at the node, then burn to adjust orbit and see what effect it has close-up.

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Thanks everyone for all of the suggestions!  I didn't get to it last night (honey do's) but I'll attempt again tonight - "bewing" 's comment about the target markers may explain a lot - after getting the spaghetti mix, I have continued to look at the target markers which always indicate the same closest approach of 2924.6km - I'll try looking for the "Pe" marker - is there a tutorial somewhere that explains all of the orbits that appear when entering another body's SOI?  I'm seeing my original orange with green actual path, then purple, brown, and sometimes a short green arc near the Mun going in the opposite direction for a short distance ... none of it looks like Scott Manley's tutorial - thanks in advance for all of your help - this community is very helpful!!

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When your orbit remains within a single body's sphere of influence (an abstraction used by KSP to determine which body's gravity will be acting on your craft at any given time; KSP's physics model only takes one body's gravity into account at a time) it will be represented by a blue line. If your orbit intersects another body's SOI then its path within that SOI will be represented by another colour. If you're currently in Kerbin's SOI but your orbit passes through the Mun's SOI then you'll likely see at least three colours: The blue representing your current orbit, yellow representing your path within the Mun's sphere of influence, and a third colour (purple, I think, but I'll have to check to be sure) representing your path after exiting the Mun's SOI and going back to Kerbin's. You might also get additional lines if that exit path ends up intersecting another body's sphere.

If you're planning on orbiting the Mun then you can ignore everything except for the blue and yellow paths since you're going to be burning your engines inside the Mun's SOI anyway so those paths won't be accurate. If you're just planning a flyby then remember that the third line is showing the trajectory that you'll be on after the flyby's complete, so make whatever adjustments are needed to ensure that it's a path you like (i.e. if you're planning on landing your craft then you'll want to get your periapsis low so that you won't have to do as much burning to get into Kerbin's atmosphere.)

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One other question or two before I try again - is there any way to alter the sensitivity of the adjustments on the manuever node?  I slowly creep very carefully extending my projected orbit into the Mun's orbit and then suddenly I have several orbits/colors displayed - when checking the Pe (I'm now ignoring the target markers - "bewing" was correct!) I discover that I have usually two and once I had four Pe's, all for later orbits - I need to "slow down" the mouse's triggering the display of orbits after touching the Mun's SOI - and the other question is why do my solid booster explode after they burn out and I decouple them?  I have to  launch three or four times before my core rocket escapes the blasts unharmed.

 

Thanks is advance again!  Y'all are very helpful!

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13 minutes ago, Garthog said:

is there any way to alter the sensitivity of the adjustments on the manuever node?

You can use the scroll wheel to finely adjust the markers. When hovered over them (not clicked) scroll up and down. It's fidgety and I don't like it but others do.

I don't know your personal opinions on mods, but there are 3 that I know offhand that allow more finely tuned maneuver node editing, down to the "set the number with the keyboard" level even:

  • PreciseNode: The granddaddy of them all and one of my personal favorite mods.
  • Precise Maneuver Editor: A different take on the above. Does the same thing but with a different UI.
  • Maneuver Node Evolved: The most "stock" feeling mod in the list, and one of the more seamless mods out there. Actually changes the maneuver node itself and gives it a few extra buttons. It has almost replaced PreciseNode for me, and it's a testament to how good PN is that I still use it in spite of MNE.
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One thing I found very helpful is that you can limit the thrust of your engine.

" the application is so sensitive as I increase the projected orbit near the Mun that I instantly "pop" into a totally different orbital arrangement"

In what I call the default view, i.e. not the map view, you can right click on your engine and limit the thrust. This allows you to get just under the target obit, and then limit your engine to like 12% or even lower, giving you much finer control of the thrust. In general, you are better off starting out a bit late than too early. If you get there after the target has passed, there in no way to recover. But if you get there a bit early, you can always go above the target orbit and catch the target as you come back down from your apo. By limiting the thrust of your engine, you should be able to fine tune the approach enough to crash in to Mun if you wanted.

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You might find things get a bit easier if you double-click on the Mun to focus your view there and then rotate the camera so that you can still see your manoeuvre node. That way you can more easily see the path your trajectory will take you in order to make the finer adjustments that you need.

In practice, though, you'll pretty much never execute a manoeuvre exactly (it's actually impossible since the nodes assume that your dV is all applied instantly) so I find it's best just to set up your node to get yourself into the target SOI, execute the burn, then do a few low-power burns in various directions to fine-tune.

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Well I tried again and was successful, but I'm still a little bewildered how I did it - to review the various colored paths, my existing course is blue with a projected (if I have a manoeuvre node) in dotted yellow/orange (?) - that path becomes purple and has the "Pe" marker with the Mun Periapsis (my closest approach?), but the path is a twisting "knuckle ball" that appears before the Mun and there's a new purple orbit (my eventual "return to kerbin" orbit?) - when I execute the manoeuvre node and stay on the course, my spacecraft enters the Mun's SOI and the paths change - now there's a new blue course going in the opposite direction towards the Mun and arcing around it with a new blue "Pe" - if I do nothing, my spacecraft follows the blue arc and passes the Mun, then hesitates for a while then makes its way to the purple "return to kerbin" orbit. Which is somewhat confusing to me and I'm really trying to understand this without using any mods so that I can "know" what I'm doing. The idea of orbiting/landing on the Mun seems even more confusing - Scott Manley's tutorial seemed straight forward compared to this. "what" 's suggestion of getting into the target's SOI implies that I need to do another burn when I get the blue arc inside the SOI - do I? I tried setting up a manoeuvre node on the arc just past the Mun to create a new "return to kerbin" orbit, but it takes too much fuel. But "what" 's description of the orbit colors seems correct.

I did try lowering the engine thrust and that did help in "sneaking up" on the SOI orbit changes! I also tried that with the solid boosters to prevent them from exploding as soon as I release them but it made no difference.

I am getting better at spelling "manoeuvre" (or is it "maneuvre", or "manoeuver"?).

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if you want to orbit the mun, you have to do another burn while in the muns sphere of influence to slow you down.  Just like your orbit around kerbin, when you raised and lowered your Ap to get the mun encounter,  when you get to the mun, your Ap is so far out, that you leave the SOI.  SO burning retrograde, (as you would to come down from kerbin orbit)  will lower the other side,  eventually bringing the Ap within the muns SOI, putting yourself into muns orbit.

 

blue is the track you are currently on,  Orange is the track that is within the targets SOI,  if you focus view on the Mun you can see what your path will look like when you get there.  Purple is your path for after you leave the muns SOI.

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