I keep missing the Mun

[KrisKelvin]

So I made a maneuver node to intersect with Mun's orbit https://imgur.com/t8aoaB4

But then when I warped to follow the trajectory, I missed the Mun (because it had gone further round in its orbit). https://imgur.com/LSFsoRL

Do I do this by trial and error? Or is there a way of calculating where to put the maneuver node so that when you get there the Mun is in the right place to capture the ship?

 

 

 

 

 

[overkill13]

If you move your maneuver node around so that your trajectory moves in front of where the moon is right now and instead intersects where the moon will be when you get there, the patched conics should show the intercept and will even give you a look at where your orbit will pass around the Mun.

[Rhomphaia]

You can drag a maneuver node around your current orbit (when the node is open drag it by the central circle) You will see when you are getting an encounter

[Grogs]

Here's what a Munar intercept looks like:

Notice that I made my maneuver where the ship was roughly pointed towards the Mun (or just in front of it) at the maneuver node. Burning prograde makes the Ap increase on the other side of the orbit, or about 90 degrees in front of the moon. Once I place the node, I add prograde until the orbit is out to roughly the Mun's orbit. Then you can 'grab' the node by holding the ring in the center and move it forward and backward until you see an intercept like this. Once you have an intercept, then you can do some fine tuning to get the Pe at the Mun where you want it.

[KrisKelvin]

3 hours ago, overkill13 said:

If you move your maneuver node around so that your trajectory moves in front of where the moon is right now and instead intersects where the moon will be when you get there, the patched conics should show the intercept and will even give you a look at where your orbit will pass around the Mun.

Yes, I did move the mode around until it was where Mun was. But that was where the Mun was when I was orbiting Kerbal. So the question is, how do I know where the Mun will be when I get there?

I don't know what patched conics are

2 hours ago, Grogs said:

Then you can 'grab' the node by holding the ring in the center and move it forward and backward until you see an intercept like this. Once you have an intercept, then you can do some fine tuning to get the Pe at the Mun where you want it.

Yes, I understand I can move the maneuvre node around. But how do I know to put it 90 degrees ahead of Mun? Did you just find that by trial and error?

Edited June 7, 2020 by KrisKelvin

[Cavscout74]

You need to aim roughly 90 degrees ahead of the Mun's current location.  This also works out to just after the Mun becomes visible over the horizon if you are doing it by eye without a maneuver node.  When you get the node in the right place, you will see the orbital path change to show the intercept

[KrisKelvin]

5 minutes ago, Cavscout74 said:

You need to aim roughly 90 degrees ahead of the Mun's current location.  This also works out to just after the Mun becomes visible over the horizon if you are doing it by eye without a maneuver node.  When you get the node in the right place, you will see the orbital path change to show the intercept

What do you mean by over the horizon? I am not viewing this from a planet, so what horizon do you mean? I am using map view

[Cavscout74]

1 minute ago, KrisKelvin said:

What do you mean by over the horizon? I am not viewing this from a planet, so what horizon do you mean? I am using map view

If you are viewing your ship, not map view, just after the Mun becomes visible over the horizon is when you can perform the transfer - that is more for if you aren't able to use maneuver nodes (like early in a career save).   In map you, you want to aim roughly 90 degrees ahead of the Mun's current position

[KrisKelvin]

So when I moved the maneuver node to about 90 deg ahead of Mun I got a bunch of new lines. But I don't know what they mean

[HebaruSan]

26 minutes ago, KrisKelvin said:

But how do I know to put it 90 degrees ahead of Mun? Did you just find that by trial and error?

An orbit that goes from ~80-100km to the Mun's orbit has a known orbital period; half of that is the time your ship will travel. The Mun has a known angular velocity, and if you multiply it by the time your ship will travel, you get how many degrees the Mun will move, which is how far ahead you need to aim. Yes, this can all be calculated manually, but in practice "trial and error" is a fair description of what people do (as well as learning to use the maneuver node UI).

3 minutes ago, KrisKelvin said:

So when I moved the maneuver node to about 90 deg ahead of Mun I got a bunch of new lines. But I don't know what they mean

If you hover the mouse over these tiny circles, they should say something like "Mun intercept". That's the projected future point when your ship will be close enough to move into the Mun's sphere of influence.

[Grogs]

1 hour ago, KrisKelvin said:

So when I moved the maneuver node to about 90 deg ahead of Mun I got a bunch of new lines. But I don't know what they mean

The orange colored line you outbound path if you execute the maneuver. Then the purple shows your path inside the Mun's sphere of influence. Finally, the green would be your new orbit after passing by the Mun. You've got a good intercept with the Mun now, so check what the Pe on the purple path is. You can fine-tune that by reducing the amount of prograde in the maneuver to bring it in to where you want for a close encounter.

[RoninFrog]

4 hours ago, KrisKelvin said:

Yes, I understand I can move the maneuvre node around. But how do I know to put it 90 degrees ahead of Mun? Did you just find that by trial and error?

If you click on the Mun and then "Set As Target", when the maneuver trajectory crosses the Mun's orbit it will put a little blue marker on your orbit and the Mun's orbit.  Then, move the maneuver node around until the two markers are near each other, and you should get an intercept.

For the Mun, it happens to be around 90°.

[king of nowhere]

5 hours ago, KrisKelvin said:

So when I moved the maneuver node to about 90 deg ahead of Mun I got a bunch of new lines. But I don't know what they mean

 

as a rule of thumb, whenever you get a bunch of new lines it means your probe will be encountering some other celestial body that will change its original trajectory. in your case, it means you are encountering mun. you found your intercept. and if you put your focus on mun, you will see the trajectory you will make in its sphere of influence.