Right... Dunas annoying now

[thevegimobil]

Ok so I've been trying for duna for ages now and I have used the illustrated guide and the protractor plugin. My ship has more than enough delta v and I'm still not getting an encounter... I'm waiting for the ejection angle for which the illustrated guide says 150 and I can't get an encounter. Also the protractor plugin has a different one so I tried that as well 200 but I can't get an encounter please help ASAP!

[amore555]

How I do this without any maths:

Get into a circular orbit, slightly smaller than Duna's, time warp till the planet appears to be near enough next to your ship on the map view, then burn prograde to increase your orbit until the conics system predicts a SOI change. Takes a while but it works.

[Aphox]

Are you sure you're prograding enough? You might be too early in your orbit to even get an encounter. Or did you try prograding way out past Duna and still didn't get an encounter?

[thevegimobil]

I'm programming and watching the map the entire time... I've tried both ejection angles given to me by my resources but nothing appears... So I then keep going past the orbit till I run out of fuel looking for an intercept

Also if there is any maths I'm not bothered about doing it I just don't know the equations

[Aphox]

You don't need any math. You must be making an error in the way you're calculating your angles, because the numbers given to me by Olex work perfectly every time. Would you mind uploading a screenshot of what your map looks like at the point you prograde to transfer?

I also might suggest locating the beta .dll for MechJeb; the automated landing system is broken due to it's beta phase, but it does give you planetary phase angle as well as escape angle in the orbital information and PPA tabs.

Another thing I must ask is have you modified your conic patch limits and draw mode in your settings.cfg folder? If not, are you out of Kerbin orbit completely before looking for an encounter? If you haven't escaped Kerbin and haven't modified the values in the CFG, you will not see future encounters until you escape Kerbin into Kerbol orbit.

Edited September 26, 2012 by Aphox
Conics

[thevegimobil]

Yeh I have patched my conics to 4. I've got mechjeb but am using the data from ilex and in game protractor plugin for all my angles. To be honest the map looks as it should from what I've seen... I'm sure I'm either burning at the wrong point or my angles are wrong but the phase angle for duna is 44.36 and I wait for it every time and then burn but never get it...

[Aphox]

Well, if all your numbers are correct (including ejection angle), and let's assume they are, how is your inclination? Have you tried modifying incline to attempt to get an encounter? I would open the debug menu and enable infinite fuel just to test it out and see if you can get an encounter pushing either incline direction. You probably won't get an encounter if your incline is far off from an equatorial Kerbin orbit. Use MechJeb to thrust toward NML+ and NML- and see if that does anything. Debug menu is shift+control+alt+D if you weren't already aware.

When all else fails, infinite fuel to see what's going down.

[thevegimobil]

Ok I will try. Also the ejection angle, is that the angle at which you burn or the angle at which you should have reached your ejection velocity?

[Jesrad]

You have to be very careful to get an encounter with Duna: its SoI is very very small relative to the size of a Kerbol orbit, so the precise moment where you get your trajectory close enough passes extremely fast while you are burning. I think that you may have missed that moment and kept burning.

When you get to about 85-90% of your predicted ejection speed, reduce throttle to the minimum. Even at 2-5% throttle you have to be quick to kill the thrust and not overshoot.

[Cykyrios]

Ok I will try. Also the ejection angle, is that the angle at which you burn or the angle at which you should have reached your ejection velocity?

It would be both, ideally, because in most equations, you assume an instantaneous change in velocity, so I tend to burn a bit before the ejection angle to compensate for this (nuclear engines don't help with their low thrust). And then again, you probably won't have an encounter just as you stop burning, and will have to do some course correction at some point (though there are times you don't need to).

[Aphox]

Ok I will try. Also the ejection angle, is that the angle at which you burn or the angle at which you should have reached your ejection velocity?

Teehee. This is your problem right here. It's neither, actually!

Your ejection angle is your angle relative to Kerbin's prograde (it's orbit line when you zoom out, or the shadow of the sun on the planet). I'm going to quote myself from a thread I just explained this in.

Planetary Phase Angle, as far as KSP goes, is the angle of your target planet in relation to Kerbin, your planet. Think of it like a clock, and Kerbin is at 3 o' clock, and Duna is at 12 o' clock. Duna's planetary phase angle would be 90 degrees. According to the interplanetary calculator at http://ksp.olex.biz/, ideal phase angle for Duna interception and capture is 44.36 degrees, which is an acute angle, which is slightly over halfway between 12 and 3 on the clock. A picture is shown on that website describing what I mean.

Ejection or escape angle is a little hard to describe. If you zoom way out in map view, you'll see an orbit line coming out of every planet. That is the planet's prograde. It follows that line.

Your ejection angle is the angle of your ship in relation to that line on a vertical axis. The website also shows pictures. The blue line coming out of Kerbin in the picture is Kerbin's prograde, and that angle is where your ship needs to be for a proper ejection to occur in order to achieve an encounter.

An easier way to see Kerbin's prograde as by looking at the shadow. It's basically always line up with Kerbin's prograde. The shadow follows the same direction as the prograde line, at least when you're zoomed in that far.

The new MechJeb beta .dll gives very accurate, detailed information about phase angle and ejection angle if you wish to download it. You can find it in the KSP mod forums under plugin-powered mods.

The clock comparison also applies to ejection angle.

Actually I think I understand the context of your question now. You want to burn at your ejection angle. I thought you meant the angle of your ship, haha. Still, that quote has some good info in it that might clear things up if you're still fuzzy. Some people burn a few degrees before hand because it takes a while to get your apogee up that far.

Make sure you turn down your throttle when you get close to lining your orbit up. Don't want to overshoot!

Also, if you want to get a closer encounter, modify your inclination slightly after you've gotten the encounter on your map. I've managed to get from 35 million meter encounters down to 100K just with incline shift.

It would be both, ideally, because in most equations, you assume an instantaneous change in velocity, so I tend to burn a bit before the ejection angle to compensate for this (nuclear engines don't help with their low thrust). And then again, you probably won't have an encounter just as you stop burning, and will have to do some course correction at some point (though there are times you don't need to).

Also that.

Edited September 26, 2012 by Aphox
Whoops, context

[thevegimobil]

Absolutely nothing!!! So frustrating... Used imfinate fuel and pro graded and retrograded along dunes orbit and no encounter...not 1 minmus and Mun go in the way but not enough to effect the orbit?.. Went way past the required delta v but nothing absolutely nothing!

[Aphox]

That is very strange. Think you could screenshot a map view of where Duna is and where you are near Kerbin? Who knows, maybe your numbers are off somehow. Might not be your fault.

[Grizzlol]

In my low-thrust craft I need to start the transfer burn up to 20 degrees earlier than the ejection angle given by Olex, which is a ridiculously high number considering, so I find it hard to believe that someone can find an encounter perfectly every time with every ship in every configuration.

The best way getting around to correcting the transfer burn (or anything else for that matter) is to use multiple saves. It pretty much guarantees success, provided of course that you have enough fuel. It is only a question of time and effort (less than using only one save). It also allows for a lot more experimentation, which is a great way to learn. Let me explain:

1. Open the saves folder in your main KSP folder. From there, open the folder with the corresponding player name (or game name, whatever it is), in which you can find the "persistent.sfs" and "quicksave.sfs" files.

2. The quick save file can be copied and renamed freely like any windows file, thus granting you a practically infinite amount of saves. I am sure some people would consider this cheating but why use quick save to begin with then? Just keep in mind that when you press the F9 key (or whichever hot-key you use for loading quick saves), the game will only ever load the file with the name "quicksave.sfs". Also, never touch the "persistent.sfs" file. You do not need to backup the original quick save or anything of sorts. The game always generates a new one when you quick save.

3. Quick save your game every time you make a major change in anything. Then also copy the quick save file and re-name the copy to something that makes you remember what it is. The copy can later be named back to "quicksave.sfs" (you obviously need to remove the current "quicksave.sfs" first, which is okay because you made a copy), and then it will be loaded as normal. This does not require a restart of the game. This is easier to do in windowed mode.

4. Just before you start the transfer burn, save the game and copy the save file. Finish the burn only in terms of velocity required (get the sun apoapsis as far out as it needs to go, relative to target orbit, ignoring any inclination or eccentricity). Now save the game again (remember to copy).

5. Warp all the way to apoapsis to see if they actually get close to each other. If you get close enough to be able to correct the orbit from before you started warping (but after you finished the burn), load the save file in which you had just finished the burn and correct it. If it is way off, note whether your ship was early or late compared to the target, then load the save file in which you were about to start the burn.

6. Redo the burn. You will have to start burning earlier or later than given ejection angle, depending on whether you were early or late, as mentioned in step 5. Repeat step 4 to 6. To make this less tedious, use phys-warp (alt + < and alt + > , or alt + whichever keys you have warping bound to). This allows up to four times warp while burning, but be careful not to diverge from your intended course. Unless your orbit is way off in every respect, at this point, you only need to redo the transfer burn until your ship and the planet arrive at the same place at the same time (again, only in terms of velocity requirements, as mentioned in step 4). This does not necessarily have to be at the sun apoapsis. If it is all wrong, however, you will have to improve your orbit around the origin body before even starting the burn, or perhaps read up more on how to actually perform interplanetary transfers.

7. The above does not have to be perfect. Once I am happy with it, I usually warp to and make a save at the sun periapsis, as this is a good place to change inclination, and is outside of the origin SOI, which allows for corrections without being affected by the origin body's gravity, while still being very far from the target. Now, knowing that your ship and target will arrive at the same place at the same time, you can feel confident in the fact that you will eventually find an encounter without correcting too much. So keep correcting it until you do.

8. Soon enough, you will find an encounter. At this point, I save the game. This allows you to start doing the corrections all over again (after having found the encounter), in case you would end up missing the planet after all, but this should not happen.

9. Do corrections as early as possible, starting from the moment you find an encounter. Observe whether the target body periapsis is above, below, to the right or left of the body, and correct accordingly. Keep a close eye on the periapsis distance from the body as you are making the correction. Keep burning until the distance starts to increase again, then you will need to correct at a different angle. If you can not see where the periapsis is relative to the body then you are too far away and you can go ahead and warp closer by about half the remaining distance. Then start correcting again. I recommend targeting (focusing the camera on) the sun, to start with, as it will put the camera closer to the encounter which makes it easier to see, until your ship is closer. Keep doing this until the periapsis is at most 1 million km from the body, preferably less (depends on its gravitational force).

10. Once the periapsis is close enough to the body, it is safe to warp all the way to the SOI. If you are planning to use the atmosphere as a means of braking (recommended), do not blindly do retro-burns to get the periapsis close enough. It is usually a lot more fuel efficient to correct the trajectory at either 270 or 90 degrees, provided that you entered the SOI horizontally. Remember that the attitude indicator (the blue and brown ball) always is relative to the body the ship is currently orbiting, and that "up" is always due North (0 degrees), "down" is South (180), 90 is the the way everything spins (anticlockwise), 270 is the opposite, the dot in the circle on the blue side (the position it is in when you are on the launchpad) is straight away from the planet, and the other way around, always.

11. Save often and copy every save file. Learn from your mistakes you made and do it better next time.

Sorry for the huge reply but ample problems call for ample help.

Edited September 26, 2012 by Grizzlol

[Aphox]

In my low-thrust craft I need to start the transfer burn up to 20 degrees earlier than the ejection angle given by Olex, which is a ridiculously high number considering, so I find it hard to believe that someone can find an encounter perfectly every time with every ship in every configuration.

This is very true. There's a limited window of time you have to achieve an encounter and you may have already passed it by the time you get there, depending on the power behind your thrusters.

[thevegimobil]

[ATTACH=CONFIG]33649[/ATTACH] that's at my lift off time it's a little ahead oh 44.36 but that allows for manoeuvres. Thrust is 850 at ejection angle so I will try and burn for longer earlier next try... Anyway there's the photo...

EDIT. Ok I wait and do the burn early and I keep burning but my ap doesn't even get close to the orbit... I have a thrust of 850 and it slows exponentially at 16 mill altitude...something is horribly wrong.... I'm using some nova punch packs if that's makes a diff

Edited September 26, 2012 by thevegimobil

[Markus Reese]

Duna the easy way without any math or hassle.

1. Get kerbol orbit

2. Adjust orbital plane to parallel if needed.

3. Burn so your orbital path will arrive a bit before duna gets to that position.

4. Keep a slow burn to elongate your orbit past duna.

5. If you are going to arrive very early, burn at apo to increase your duration you are traveling slower than duna.

6. Interception.

This works for me every time provided I don't arrive late or get there horrendously early. Never ever have had to use a protractor/calculator/etc. So I spend a bit more on fuel. Slow burn and efficent engines make it fun.

[nhnifong]

[ATTACH=CONFIG]33649[/ATTACH] that's at my lift off time it's a little ahead oh 44.36 but that allows for manoeuvres. Thrust is 850 at ejection angle so I will try and burn for longer earlier next try... Anyway there's the photo...

EDIT. Ok I wait and do the burn early and I keep burning but my ap doesn't even get close to the orbit... I have a thrust of 850 and it slows exponentially at 16 mill altitude...something is horribly wrong.... I'm using some nova punch packs if that's makes a diff

You can take a screenshot with F1 (fn-F1 on a mac). Upload it to imgur for full resolution.

[thevegimobil]

Yeh but I'm on the forums on my iPad so it was much quicker and easier..... I'm annoyed cos no matter what I do I cannot reach duna at all..

[Markus Reese]

vegi, put up a pic of your rocket. I know I had issues because I overthought the setup. Once you get orbit, it is the hardest part. you said you had the fuel and ship to reach so not sure what could be causing it if you get that alignment.

[nhnifong]

Wait a little longer than the reccomended planetary alignment. Duna will be too far ahead. Then, in solar orbit, raise your apoapsis to "scan" duna's orbit with the intersection. If your inclination doesn't suck you will see the duna enounter light up for a split second. Have your finger on the x key!

[robtherad]

Here's how I get to Duna using enigma's protractor mod. http://kerbalspaceprogram.com/forum/showthread.php/21544-Plugin-Part-17-Protractor-Planet-Moon-Rendez-Mod-v-2-1-4

Just strap Jeb's calculator somewhere onto your spacecraft and click launch.

On the launch pad you'll see the information window pop up. You'll want to match the two underlined values up. One is your current phase angle, the other is your desired phase angle.

Go ahead and time accelerate on the launch pad until they are matched up. Now you can go ahead and launch your rocket into orbit around Kerbin. I recommend heading east (90 degrees) when you are doing your gravity turn since you already have some velocity in that direction from the rotation of the planet.

Once you're in a circular orbit, look at the information window from the plugin. You'll want to pay attention to your current ejection angle and the ejection angle required to get to Duna. The ejection angle assumes you are instantly changing your velocity to the amount needed to get to Duna so you will want to start your burn a bit earlier than the listed ejection angle.

I started my ejection burn at about this ejection angle. If you are using a NERVA like me, you can hold alt and press (.) a few times to engage physical time warp. After a few minutes I had changed my velocity enough to make it into Duna's SoI.

Here's the final result. If you want to hide the plugin information, click the calculator in the bottom left of your screen and the info box will minimize. Click it again to bring it back.

Hopefully this should alleviate your frustration and get you to Duna.

[thevegimobil]

Everyone thank you... I got there on my own eventually.... It turns out that olex's ejection angle to duna is wrong... The protractor had it right all along. Anyway was happy when I finally got an intercept... Everything was fine olex just gave me the wrong angle

[Sluggy]

I had exactly this same problem. Made it to Duna three times in a row and from the fourth on I couldn't even come close. The answer to these woes isn't easy but it is simple. I'll give you a hint: Olex's numbers aren't wrong... if you are assuming a circular orbit.

Happy Flying

[thevegimobil]

Ah because duna is eccentric?...