Difficulty using navball to anything outside kerbal orbit

[Chris_C]

I have no trouble plotting a course to the Mun or Minmus, and I can quite easily plot a course on the navball which will put me in the targets SoI.

However when I try to plot a course to say Duna, I seem to find it very hard to even get a near encounter.

At first I thought it was because the UI wouldn't allow me fine grained control, so I got a plugin that allows fine grained control either numerically or in steps of different orders of magnitude.

I doesn't seem to matter what time the maneuver is set for or what setting I use for the 3 axes I just can't seem to get a decent plot that would at least get me inside the SoI.

Obviously although for basic use I'm okay, I must be doing something wrong....

any ideas?

Edited September 11, 2013 by Chris_C

[blizzy78]

Are you plotting your course using maneuver nodes? Please post a screenshot that would show how you are doing that.

[KerbMav]

Are you timing your departure for a reasonable planetary alignment? http://ksp.olex.biz/

At the right time, try targeting the planet and creating several nodes:

One to bring your orbit around the star close to the one of your target, then one on the AN/DN point of the plotted course to align the inclination (up and down).

[Chris_C]

Are you plotting your course using maneuver nodes? Please post a screenshot that would show how you are doing that.

sorry I don't do flikr or social media so have no where to post it, as explained I am using maneuver nodes, I'm waiting till duna is roughly 30-40 degrees ahead of kerbin, I've tried advancing the node any number of orbits round kerbin but it doesn't seem to improve stuff or make it worse???

[M4ck]

Use imgur for posting pictures. No information about you is needed, it's just a matter of creating an account(mail+password) and uploading whatever pictures you want.

By the way, you can not "advance the node any number of orbits" unless you place the node in that place using mods, if you try to do this manually, it will simply slide along one orbit again and again.

Edited September 10, 2013 by M4ck

[Synapse]

You need to align your AN/DN to 0 degrees by burning north or south before you can make a encounter appear

[capi3101]

So you're not getting an encounter with Duna, though it's in phase. Okay - this is a fairly common problem, and you have to treat it like a game of golf a bit.

So what you need to do is make sure you set your maneuver node about 150 degrees from the prograde direction of Kerbin's orbit (about the 5:00 position or so). Start yankin' on the prograde marker until you get a Kerbin escape. Zoom out, and keep pullin. Eventually when your path starts crossing Duna's orbit, you'll see the little encounter chevrons appear (provided you've selected Duna as your target, of course). At that point, you're going to want to see what happens to the distance of closest approach when you fiddle with the node further. If you pull prograde more and the distance decreases, great. If you pull prograde and the distance increases, pull retrograde. I find that I often have to pull radial-in burns to get an encounter with Duna; that can be avoided by adjusting the position of the maneuver node itself, but you have to zoom all the way back down to your orbit around Kerbin to do that. I'll just say if you can avoid a radial burn, good. Now, Duna is in a slightly different orbital plane that Kerbin, so you should also play with the normal/anti-normal nodes as well.

If you can't get an encounter on your first go but are getting awfully close, or if you do get one, pull your burn and discover after the burn that you don't have a Duna encounter anymore, DON'T PANIC. Hitting another planet is kinda like a game of golf - you've teed off, now you just need to evaluate where you are and plan what you need to do to get on the green (in this case, in the target's SOI). That means a correction burn. There's no shame in correction burns; hell, NASA did that all the time with Apollo. Same deal - though the earlier you set up the correction burn, the less delta-V you tend to spend in the process. Me, I wait until the ascending/descending node regardless of where that's at. Same deal - set up the node, play with it and see what it does with your orbit. Oftentimes you won't need more than 100 m/s of delta-V to correct.

That's about all the advise I can give you. Only other thing I would mention is that until you get it down pat, pack some extra delta-V into your transfer stage...maybe as much as 150% of the amount indicated by the wiki's delta-V map. The delta-V map assumes optimal conditions/a best case scenario, which a novice is not going to be able to affect (not without mods anyway). Extra fuel gives you room to screw up and still get there and back. Worry more about optimizing things when your skill has improved.

Aerobraking for Duna works well at 12,500 m. Don't go below 11,000 or you're going in whether you want to or not. Good luck.

[Chris_C]

So you're not getting an encounter...

thanks for the help, but that's kinda what I'm attempting anyhow...

afaict it seems if you set off on a course with say a 5Mkm closest encounter, there seem no way you could possibly have enough delta-v to get to Duna.

I'm flying a probe with 3000+m/s/s spare dv, and a 5 * TtW ration

rather than just stabbing round at it, I really want to understand why it is I'm going wrong, then I stand a chance at solving it...

[LeadMagnet]

. There are loads of LPers that detail this exact mission. And some of them a funnier than hell!!

[Chris_C]

LOL - that guy just got an encounter by random chance - he said as much himself!

[LeadMagnet]

LOL - that guy just got an encounter by random chance - he said as much himself!

Like I said, funnier than hell! Random or intentional...I'LL TAKE IT!!!

[Specialist290]

Another thing I thought of that might be throwing you off just a little: Inclination differences.

Chances are, you're performing your injection from a slightly inclined orbit around Kerbin. Over the distances that you need for interplanetary travel, a slight inclination difference can magnify your distance by several million meters.

Go ahead and set up a node in Kerbin orbit that gets you a close approach to Duna. Then look at the inclination difference at the ascending or descending node that's along your flight path. At that node, plot another node and adjust your normal vectors (the purple triangles) until you get a value that's about ~0.5 or so within zero.

Combine that with the advice capi3101 has already given, and you should manage to get an encounter before too much longer. Don't get discouraged if it takes quite a bit of fiddlin' to get it right -- that's normal.

[stringyquark]

Or to see where to efficiently burn for Planetary transfers you could try the protractor mod. Use it to do a few planetary transfers, help you get the feel for it.

[SRV Ron]

Get into prograde escape velocity from Kerban. Keep the solar orbit as circular as possible. Set up a maneuver mode with Duna as a target. If you are not getting a encounter anywhere along the orbit, you may have to wait, accelerate time, until you have traveled far enough in solar orbit to get an encounter window.

Currently, I have three test probes waiting for that window to appear which is available every second or third Kerbal year from the lest one.

[Chris_C]

Get into prograde escape velocity from kerbin .....

I think I get you this is what I stumbled onto with some experimenting...

1. make a maneuver so the apoapsis is just inside the orbit of your target (not too near or capture will take a long time, not too far or no capture...)

2. wait till apo and burn prograde until you have a circular orbit, you may have to adjust some other node axes to ensure all the orbit is inside the target orbit (if 50/50 out/inside you would be catching up / falling back all the time)

3. wait till the target planet captures you.

4. if path hits target burn prograde till you get a periapsis you are happy with

5. this will most likely sling shot you away from the target, wait till periapsis and burn retrograde till you have an orbit

my only nagging doubt is this method hideously inefficient?

Edited September 11, 2013 by Chris_C

[Vanamonde]

Chris_C, your primary difficulty is not that you are doing anything wrong, but that you are trying to cross roughly 54,000,000km and then hit a target that is around 96,000km wide. Use Olex's calculator http://ksp.olex.biz/ to get close, play with a maneuver node until you get the "closest approach" markers, and either finesse those, or plot a mid-course correction to achieve the final intercept. That's how I do it.

[SRV Ron]

After 100 days in solar orbit, I got my window to send probes to both Duna and Eve. The Eve one arrives first but comes in so fast that it takes a lot of aerobraking to land it. The Duna ones 60 and 63 days later and can be slingshot around Ike to slow them down if you are lucky.

[Chris_C]

....play with a maneuver node until you get the "closest approach" markers, and either finesse those, or plot a mid-course correction to achieve the final intercept. That's how I do it.

hmm my whole point is that the finessing process is what I'm completely lost with, I think I'll just stuck with my Hohmann transfer like method...

its easy to get within 6Mkm but usually with too much dv to make it doable...

"finessing " such a maneuver just ain't happening....

[wilt57]

After 100 days in solar orbit, I got my window to send probes to both Duna and Eve. The Eve one arrives first but comes in so fast that it takes a lot of aerobraking to land it. The Duna ones 60 and 63 days later and can be slingshot around Ike to slow them down if you are lucky.

It takes 45 days to go to Duna if you launch and do a Hohmann transfer during the window. Can't remember what it takes to go to Eve, but I think it's less than 45 days.

Chris_C, finessing these maneuvers isn't tough. A couple small tugs on the maneuver node is all it takes. Or you can just point your ship in either radial direction and give short little bursts and see if your encounter PE is rising or falling. If you have a slow computer, it could take a while for it to compute the node vector you are trying to create. This could lead to the impression that finesse is not possible.

[SRV Ron]

Eve was under 45 days. Duna much longer because I aim for a low delta v burn to encounter. That encounter can be much quicker if you hit a window where Duna's orbit is closer to Kerban at the location of intercept or you waste fuel by extending your orbital loop much further out from Duna.

Fine tuning an encounter can be done using short burst from monoprop thrusters. Getting the encounter on plane is more fuel efficient then coming in from the pole. I had one fine tuned to crash on Duna before the burn. Unless everything is timed to the milisecond, the results will just be close. But, that is what mid course corrections are used for.