Rendezvous help?

[RedPandaz]

How do people ever figure out where other planets and stuff are going to be? Help? Haven't even been able to get to the moon cause of this

[George van Doorn]

Well, let's start with the basics. How do you figure out where a car is gonna be 10 seconds from now? You see where it's headed and you estimate its speed if you don't know it. For the Mun and all the other planets, we know they stay on their nicely drawn circles called orbits. Each body has a different speed. You can find the orbital speeds and the orbits here:

http://wiki.kerbalspaceprogram.com/wiki/Mun

But who wants to calculate all that stuff? You want a fast answer, right? And here it is: Imagine a line between Kerbin and the Mun. The Mun will be travelling counterclockwise so we are pretty sure that in the near future it will be a bit more counterclockwise. Imagine another line on this counterclockwise direction that does about 60 degrees with the first one (Kerbin-Mun). Don't worry about the exact number, the Mun's sphere of influence is pretty big and I might also estimate it wrong (I do it based on eyeballing and knowing the deltaV). Anyway, you want to have a trajectory from your low Kerbin orbit that reaches that 60 degrees point on the Mun's orbit. So when you plan a maneuver, the highest point of your orbit should be around his imaginary point making a 60ish degree angle with the Mun's actual position.

For planets like Duna, Dres and all the rest, you can use plenty of tools that basically tell you: OK, the planets align on day X, you have to go in that direction with that precise speed and you'll encounter it.

Here are some of 'em:

https://alexmoon.github.io/ksp/

http://ksp.olex.biz/

Transfer Window Planner mod

Kerbal Alarm Clock can also tell you when the transfer windows occur.

 

Oh and just for the Mun there's a very easy one if you have a mod called Precise Node or Precise Manuever or so. From your low Kerbin orbit (70-100 km), add a new manuever node, just type 860 in the prograde marker and then move the node on the orbit until you get an encounter :). You can also just drag the prograde marker until you see 860m/s2 (ish) and then change its position.

Edited February 9, 2017 by George van Doorn
improving the answer

[Vanamonde]

Thread moved to Gameplay Questions, since it's seeking help rather than offering it. 

[Ohm is Futile]

Good first answer, especially if you like the technical side of things.

In practice, people use the information from the tools @George van Doorn told you about to help them create a maneuver node. The maneuver node will give you direct visual feedback of where you will be and where your target will be if you get close enough with your maneuver node (close enough does not need to be close at all).

[Snark]

Also, one other thing.  You can slide a maneuver node along your orbital path if you grab the center and drag it.

So, if you're in LKO and you want to go to the Mun... and if you don't want to try to figure out where the node should go... just drop it anywhere, then drag the prograde handle until your Ap rises to approximately the Mun's orbital altitude.  Then just grab the center of the maneuver node and slide it around your orbit until you see that your path will enter the Mun's SoI.

Sorry if that seems like a stupidly obvious question... but I was playing KSP for over a year before I found out about that feature.  Made things so much easier, in so many circumstances.  Maybe not everyone's as slow on the uptake as I am ... just wanted to make sure you know you can do this.

 

Of course, that approach doesn't directly help you in predicting interplanetary launch windows (i.e. "where does Kerbin need to be for an efficient launch to Duna" or whatever), but that's what tools like http://ksp.olex.biz are for.

If you'd prefer not to rely on an external tool, here's a sneaky way to use the drag-the-node approach for figuring out interplanetary launch windows:

Make a small, lightweight, cheap satellite, and launch it so that it just barely escapes Kerbin's SoI with very little Kerbin-relative velocity.  Now you have a satellite orbiting the Sun, in pretty much an identical orbit to Kerbin's.  Just leave it parked there, name it "Orbit Planner" or something.  Okay, suppose you later decide "I want to launch a mission to Duna" (or wherever).  Go to your orbit-planner satellite, drop a maneuver node anywhere on its orbit around the sun, drag prograde until its Ap touches Duna's orbit, see the markers that show how far away your closest approach is.  Now just drag the maneuver node around the orbit-planner's solar orbit until you see the markers converge.  There.  That's where Kerbin will need to be when it's time to launch your Duna probe, and the timer on the node is the time until your launch.  Once you've got the needed info, then you can just delete the maneuver node from your orbit-planner satellite, and it's ready for its next use.

(Caution:  if you use this technique for planning interplanetary transfers, do not use it for estimating dV requirements, because the dV for "transfer from circular solar orbit" will be a lot bigger than the dV for "transfer from LKO", due to Oberth effect.  It's useful for planning when to launch, but not for how much of a burn you'll need, other than setting an upper limit on it.)

[RedPandaz]

On 2/9/2017 at 2:18 PM, Ohm is Futile said:

Good first answer, especially if you like the technical side of things.

In practice, people use the information from the tools @George van Doorn told you about to help them create a maneuver node. The maneuver node will give you direct visual feedback of where you will be and where your target will be if you get close enough with your maneuver node (close enough does not need to be close at all).

The node doesn't help me know when the Mun will get there tho- and what if it's, say, on the other side of the planet?

[George van Doorn]

2 hours ago, RedPandaz said:

The node doesn't help me know when the Mun will get there tho- and what if it's, say, on the other side of the planet?

Ah, yes, obviously! I forgot to mention one important thing!! Click on the Mun and then click on "Set target". You can do that with every body you wish to reach. And then, when you draw a maneuver node, it will tell you how close to the target you'll be the closest (if you're close enough; if you are always far, it wouldn't tell you).

[FireBlast]

It's very simple to get a Mun encounter just put a manuever node and blast prograde until your orbit reaches the mun's. If you don't get an encounter move the node around your orbit unill you get one. Hope it helped.

[Carraux]

To get a proper Mun encounter:

1. In map view rotate your view so that you are directly "above" Kerbin and look "down".
2. Rotate then your view that Mun is on 3-O'clock position ("east"). You may want to zoom out for this.
3. Place the maneuver-node on 6-O'clock position ("south") and drag the handle prograde until your path hit Mun's SOI.

Bingo! 

[BentRim]

On 2/10/2017 at 8:28 AM, Snark said:

If you'd prefer not to rely on an external tool, here's a sneaky way to use the drag-the-node approach for figuring out interplanetary launch windows:

Make a small, lightweight, cheap satellite, and launch it so that it just barely escapes Kerbin's SoI with very little Kerbin-relative velocity.  Now you have a satellite orbiting the Sun, in pretty much an identical orbit to Kerbin's.  Just leave it parked there, name it "Orbit Planner" or something.  Okay, suppose you later decide "I want to launch a mission to Duna" (or wherever).  Go to your orbit-planner satellite, drop a maneuver node anywhere on its orbit around the sun, drag prograde until its Ap touches Duna's orbit, see the markers that show how far away your closest approach is.  Now just drag the maneuver node around the orbit-planner's solar orbit until you see the markers converge.  There.  That's where Kerbin will need to be when it's time to launch your Duna probe, and the timer on the node is the time until your launch.  Once you've got the needed info, then you can just delete the maneuver node from your orbit-planner satellite, and it's ready for its next use.

(Caution:  if you use this technique for planning interplanetary transfers, do not use it for estimating dV requirements, because the dV for "transfer from circular solar orbit" will be a lot bigger than the dV for "transfer from LKO", due to Oberth effect.  It's useful for planning when to launch, but not for how much of a burn you'll need, other than setting an upper limit on it.)

Excellent tip @Snark

I really struggled with the stock node tools and found that Precise Maneuver made node planning much more manageable.   

[Hodari]

Also, for the Mun at least, if you don't even have maneuver nodes unlocked yet, you can get a reasonably good encounter by just getting into a low Kerbin orbit and then time warping until you JUST see the Mun start to rise in front of you, then switch to map mode and burn prograde until it shows you getting the encounter.

[WanderingKid]

On ‎2‎/‎14‎/‎2017 at 8:52 PM, Hodari said:

Also, for the Mun at least, if you don't even have maneuver nodes unlocked yet, you can get a reasonably good encounter by just getting into a low Kerbin orbit and then time warping until you JUST see the Mun start to rise in front of you, then switch to map mode and burn prograde until it shows you getting the encounter.

If you don't have maneuver nodes, you most likely won't have upgraded the Tracking Center and thus won't have conics, either.  However, you just get your apoapsis up to 11 million using the MunRise technique and you'll eventually capture.  This will only occur in Career mode, however.