How to get a duna encounter without mechjeb (problem with manuver nodes)

[Kerbalyer]

Alright, so I'm having trouble getting a Duna encounter even if I use a maneuver node, so can you give me some tips on how to get to Duna please?

Edited May 22, 2022 by Kerbalyer
I just realized how to post images.

[Bej Kerman]

37 minutes ago, Kerbalyer said:

Also, some tips on how to get to Duna please?

Elaborate please

[Kerbalyer]

I know how to make a maneuver node, but I just can't seem to get an encounter without mechjeb.

Also my rockets have enough delta V but the maneuver node is my only problem.

[Vanamonde]

I'd suggest trying some practice flights between Mun and Minmus, or vice versa. It's the same problem in terms of piloting and geometry but much easier to hit the targets.

Do you have a screenshot of your closest approach markers around Duna? 

[Kerbalyer]

Here ya go. Imgur: The magic of the Internet

 

[king of nowhere]

so, you can do it the easy way, or the hard way, or several harder ways. let's discuss the easy way.

you start from kerbin, equatorial orbit, during the time of the transfer window with duna. to calculate the transfer window time, i suggest using alexmoon tool. Select Duna as your target.

To reach Duna, you are supposed to burn for 1000 m/s, more or less. So make a prograde 1000 m/s manuever node. Anywhere in the orbit. You are unlikely to make it in the right place, but we'll fix that.

Zooming out on the map, look at your solar apoapsis. Depending on where you place the manuever node, you get different solar apoapsis. Now move your manuever node around the orbit, you'll see your projected solar apoapsis move too. Move your manuever node until you find the position that will give you the maximum solar apoapsis. That's the most efficient place to make the burn, and it should give you an apoapsis on Duna's orbit.

If your apoapsis is not exactly on Duna's orbit, change the burn. If you're going past Duna, reduce the burn, if you're too low, increase the burn. After you do that, change again the position of your manuever node; the optimal position changes with how much you're burning. But for small changes, it's negligible. So, suppose after placing your 1000 m/s node you saw that it falls short, so you increased it to 1050 to touch duna's orbit. Then you move again the manuever node, and you see that you can get a bit past duna. Now you reduce the burn, say to 1040, and you're touching the orbit, and you didn't make enough of a difference to be worth moving the node.

Do be careful; a handful of m/s more or less may throw out an encounter.

Now you probably won't be seeing a close approach marker. That's because you only see them when you are actually touching the target orbit, and even though your apoapsis is as high as duna, you're not touching it, because of orbital inclination. You should be seeing the ascending and descending nodes.

So you plan a second burn on the planar node closer to you; if it's the ascending node, plan a burn downward, on the descending node a burn upward. This will reduce planar inclination. When inclination becomes 0, you should see a close approach marker, and you should be close to it. Refine the burns by trial and error to get an actual encounter.

Keep in mind that you will have to plan correction manuevers later, because no burn is exact. but they will be small.

be careful that mun doesn't get in your way. You could use it to get a gravity assist and save fuel, but that's harder. You also can avoid the plane change and make sure you meet duna on the manuever node, and it often saves fuel, but again, it's harder.

 

You are doing all this because your objective is to raise orbit. to raise orbit you want to burn prograde, except that you are orbiting a planet orbiting the sun, so it's a bit skewed. So you want to leave the planet on a trajectory that's prograde compared to the planet; that will be the best way to move away from the sun; similarly, you'll want to leave retrograde to move to the inner planets. But it's not easy to find the best way to burn around the planet to leave prograde compared to it, because you're still moving around the planet; that's why you do it by trial and error, moving the manuever node by small increments.

At this point, you ensured that your apoapsis will be as high as duna's orbit. Being at the right time in the transfer window will also ensure that duna will be passing there just when you do. but you're still not done, because the orbits have different inclinations; you'll pass above duna, or below it. matching inclination is the simplest way to fix this problem, though it's often not the optimal one.

24 minutes ago, Vanamonde said:

I'd suggest trying some practice flights between Mun and Minmus, or vice versa. It's the same problem in terms of piloting and geometry but much easier to hit the targets.

 

Seconded

4 minutes ago, Kerbalyer said:

Here ya go. Imgur: The magic of the Internet

 

In both cases, it seems your problem is that you did not launch at the proper transfer window. so you touch duna's orbit, but duna is not there.

Edited May 22, 2022 by king of nowhere

[Vanamonde]

Yes, looks like it's timing rather than navigating that's the problem. I like this calculator because it doesn't do too much of the work for me. https://ksp.olex.biz/