Help with landing on duna

[Darth C3P0]

ok I have a bit of a problem here
so I launch when duna is 45 degrees from me and the sun as shown below

and when I do my encounter burn, I wait until I get to that encounter. But the problem is duna is above me
WAY above me.
Should I wait for a more accurate 45 degree angle? I was launching a bit past it actually, it was more like a 40 degree angle instead. Or should I keep it the way it is? Trying to burn radial takes up a **** ton of fuel and I keep running out so how will I do this?

note this isnt actually my image.

[The Aziz]

Any sort of transfer window calculator is your answer. I mean, you could wait and watch, trial and error but this is time consuming. But..

When you set your maneuver node, and make it so it reaches Duna orbit, make sure you set it as target, then it will show you closest distance. Then you can say if you reach Duna too early (target position behind closest approach) or too late.

[Snark]

15 minutes ago, Darth C3P0 said:

and when I do my encounter burn, I wait until I get to that encounter. But the problem is duna is above me
WAY above me.

Not sure what you mean by "above".

15 minutes ago, Darth C3P0 said:

Should I wait for a more accurate 45 degree angle?

It shouldn't matter much.  Basically, there's a certain angle which is the "ideal" angle for the minimum-possible dV transfer.  That's the ideal to shoot for... but if you're a little off, it doesn't really matter all that much, it just means that you'll need a bit more dV.  The farther off from the ideal window you are, the more dV you'll need.  If you're only 5 degrees off, that should be just fine, it shouldn't make that much of a difference.

If you're finding that your trajectory is way way off, that means you're doing something else "wrong"-- i.e. the problem isn't the relative positions of Kerbin and Duna, it's something about the way you're setting up your transfer burn.  Maybe you're burning the wrong amount, or in the wrong direction, or something.

Here's a handy transfer calculator that should give you a basic idea of how to do it:  http://ksp.olex.biz

Just tell it Kerbin as your origin, Duna as your destination, and enter the height of your parking orbit around Kerbin.  As you can see, the ideal angle between the two planets is about 44 degrees, so you're doing pretty well, there.  If you're in, for example, a 100 km orbit, then your burn will be somewhere between 1040 m/s and 1100 m/s (depending on how close to 44 degrees the planets are), and you can see from the illustration where your ship should be in its low Kerbin orbit when you do the burn.

So, just set up that burn, then look at the map view, and do any small amount of extra fiddling you may need in order to get your intercept (that will likely consist of adjusting the size of the burn a bit via the and handles, and/or sliding the maneuver node slightly forward or backward along its orbit path around Kerbin to get the approach just right).

If the above advice isn't enough to get you to where you need to be ... could you post a screenshot of your best attempt, so we can see what you're doing?  That might give us a better idea of where you could be going off the rails. 

[Darth C3P0]

I will post the screenshots soon, but what I mean is once I approach my encounter and it shows my escape path, Duna is above my rocket, which means I have to burn radial, which takes up a ton of fuel. I am just a basic astronaut, but I know what all of the maneuvering nodes are named and that good stuff, don't know much about Delta V and whatever so yeah.

Once I'm around the sun, I pull the prograde until I get that encounter, then I burn at the maneuver. Once again screenshots will come later.

I think what I might just do is in addition to burn prograde, I may try to burn normal (the node) so that way I'm more aligned since Duna is on an incline.

Edited February 12, 2018 by Darth C3P0

[Snark]

35 minutes ago, Darth C3P0 said:

I will post the screenshots soon, but what I mean is once I approach my encounter and it shows my escape path, Duna is above my rocket

Wait, you're saying that you do have a Duna encounter, i.e. that when you do your ejection burn from Kerbin, it puts you on a path to hit Duna's SoI?  And that your problem is simply "after I get inside Duna's SoI, my Duna Pe is at too high an altitude and in the wrong place"?

Oh, okay.  In that case, the solution is really easy. 

Basically, don't try to fix the problem when you're inside Duna's SoI, because that's way too late-- you'll have to burn gobs of fuel to fix it.  The earlier you adjust your course, the smaller the correction you'll need.

Therefore, instead, drop a maneuver node on your trajectory when you're still in interplanetary space, for example 20 days or more before you hit Duna's SoI.  Then you can just very gently tweak the maneuver node to put your Duna path exactly where you want it, so that your Pe is at the desired altitude and latitude.  By doing the maneuver well before you get to Duna, it means you only need a teeny-tiny burn, probably only a few dozen m/s at most, maybe even under 10 m/s.  Even a 3 m/s burn has a big effect if you do it weeks before your encounter.

Note that the easy way to fine-tune it is:  after you drop the maneuver node, but before you start tweaking it, click on Duna and choose "Set Focus".  That will zoom the map to Duna and show you exactly what your path across its SoI will be.  In that view, then rotate the camera around until you can see your maneuver node sitting out there in interplanetary space, and then tweak the maneuver node handles; you'll be able to see exactly how your path will go, and get it just the way you like it.

For efficient capture, you want your Pe to be as low as possible, in order to take maximum advantage of Oberth effect.  Of course, if you're planning on using aerobraking upon arrival (an excellent idea), you'd need to come in pretty low anyway.    But even if for some reason you're not aerobraking, you'll want to get the Pe as low as possible without hitting atmosphere, for Oberth.

[The Aziz]

In addition to what Snark said

2 hours ago, Darth C3P0 said:

once I approach my encounter and it shows my escape path, Duna is above my rocket, which means I have to burn radial, which takes up a ton of fuel.

Again. You got an encounter, see your Duna Periapsis, and you burn radial from there? Because that's what you do, well, not wrong, but slightly incorrect in this particular situation. You should burn retrograde at periapsis, that's how you get elliptical orbit. Then, and only then you can aim for different inclination and all that. Or, like @up said, weeks before encounter.

[Darth C3P0]

Thank you guys, I will try it out and see how it goes.

Also yes, I do the injection burn from Kerbin (whatever that means) and I just go interplanetary, then prograde to my target

Edited February 12, 2018 by Darth C3P0

[Darth C3P0]

Thank you guys, I made it to Duna but now have to do a rescue mission because I blew up my engine when relocating

but ye thank you guys so much

[Geonovast]

1 minute ago, Darth C3P0 said:

now have to do a rescue mission because I blew up my engine when relocating

Sounds like you're playing the game the right way.  Congrats!

[Darth C3P0]

8 minutes ago, Geonovast said:

Sounds like you're playing the game the right way.  Congrats!

Thanks, I am really bad at this stuff but I feel it being a lot easier now that I know how to get there

[Geonovast]

1 minute ago, Darth C3P0 said:

Thanks, I am really bad at this stuff but I feel it being a lot easier now that I know how to get there

It's amazing how fast the insanely difficult stuff becomes second nature.

 

[Darth C3P0]

3 minutes ago, Geonovast said:

It's amazing how fast the insanely difficult stuff becomes second nature.

 

time to learn rendezvous boys!