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Anyway to arrive equatorial?


Biggen
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On the way to Eve and have the encounter but I cant tweak my resulting Pe enough to get into an equatorial orbit. The best I can get is about a 25 degree inclination (mid course correction). Id rather get it closer to equatorial since ill be sending other landers to the same spot.

Is there a better way to arrive so Im closer to equatorial? I used the launch window planner and am leaving at the optimal time.

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I usually just try to drop the PE on the equator for an equatorial orbit ... then you can either add a normal component to your capture burn, or just barely capture, coast way out, and fix your alignment then.  Either one can work, or you can combine the two, try it out.

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The issue is that Eve's orbit is inclined slightly with respect to Kerbin's.  Just adjust your trajectory while you're still far away from Eve, long before you enter its SoI.

Note that you can focus the map view on Eve to allow visualizing your flyby path while you're doing the adjustment. First, drop a maneuver node somewhere appropriate on your solar orbit. Then focus the map view on Eve and zoom in. Then tweak your path.

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28 minutes ago, Snark said:

The issue is that Eve's orbit is inclined slightly with respect to Kerbin's.  Just adjust your trajectory while you're still far away from Eve, long before you enter its SoI.

Note that you can focus the map view on Eve to allow visualizing your flyby path while you're doing the adjustment. First, drop a maneuver node somewhere appropriate on your solar orbit. Then focus the map view on Eve and zoom in. Then tweak your path.

Yeah ive done that. The best I could do was the mentioned 25 degree inclination difference.

So I guess the only way to be sure I could arrive in an equatorial orbit would be to adjust my normals at Eve's AN/DN nodes during my flight to Eve in solar orbit, right? But if I never cross those nodes there is no way to adjust.

The launch window calculators also assume an equatorial orbit when leaving a planet. If Im in a severe inclined orbit of Eve, how do I figure my way back to Kerbin? Surely, I dont want to spend the gobs of dV to get into equatorial orbit before leaving Eve. Do I just plug in what the launch window calculators say and then tweak until I get my encounter from my inclined orbit?

Edited by Biggen
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1 hour ago, Biggen said:

The best I could do was the mentioned 25 degree inclination difference.

...Okay, I'm really having trouble picturing your situation.  Maybe a map-view screenshot of your approach, showing what your transfer orbit looks like?

Eve's orbit is inclined from Kerbin's, but only slightly; it's not like you're going to Moho or Dres, which have much more extreme inclinations.  I'm hard-pressed to see a scenario where you're literally approaching Eve from a direction 25 degrees above/below its orbit-- you should be off a degree or two at most, unless there's something badly messed up about your transfer orbit.

1 hour ago, Biggen said:

So I guess the only way to be sure I could arrive in an equatorial orbit would be to adjust my normals at Eve's AN/DN nodes during my flight to Eve in solar orbit, right?

That would be the only way to arrive perfectly equatorial, yes.  However, you can do pretty well with an inclination-adjusting burn even if you're not right at the node.

1 hour ago, Biggen said:

But if I never cross those nodes there is no way to adjust.

How is that even possible?  If you have a well-executed transfer, then your inteprlanetary orbit will cover approximately 180 degrees of its path around the sun, which means you're guaranteed to cross either the AN or the DN along the way.  The only way for that not to be the case would be if your transfer orbit is a lot less than half an orbit, which means you're nowhere close to the optimal launch window you claim.

1 hour ago, Biggen said:

The launch window calculators also assume an equatorial orbit when leaving a planet. If Im in a severe inclined orbit of Eve, how do I figure my way back to Kerbin? Surely, I dont want to spend the gobs of dV to get into equatorial orbit before leaving Eve. Do I just plug in what the launch window calculators say and then tweak until I get my encounter from my inclined orbit?

How big a deal it is depends on how your "equatorial AN/DN" are oriented, relative to the necessary ejection path from Eve.  (I put that in quotes because there's no actual AN/DN marker in map view.  I'm referring here to the conceptual points where your inclined orbit crosses Eve's equator.  I'll call them AN/DN here for brevity.)

For example:  Suppose your equatorial AN/DN are precisely 90 degrees away from where you'd need to do your burn-- i.e. your burn would need to happen when you're at the northernmost or southernmost extent of your orbit, where your heading is precisely due east.  In that case... basically you can just do your burn as if you were equatorial, with only minor adjustments, since you're traveling in the same direction you'd be traveling anyway if you had been equatorial.  It won't be precisely identical, because Eve's gravity will curve your path a bit northward or southward as you eject, which it wouldn't have done if you were equatorial; but I suspect that would be a relatively minor error that would be easy to adjust.

For another example:  Suppose your equatorial AN/DN are precisely 0 and 180 degrees from your required ejection point:  that is, the place where you'd need to put your ejection burn is right where your inclined orbit is crossing the equator.  That's easy to adjust for, too.  The answer is:  you will do an inclination change to an equatorial orbit around Eve, but not at low altitude.  Instead, you do two burns.  Suppose you're in 100 km orbit over Eve, and you've worked out that your transfer burn to go home to Kerbin is 1400 m/s.  So, first you do one burn that is enough to raise your Ap quite high, but not escape Eve; for example, say, 1000 m/s.  This burn is done prograde (that is, not due east, but in the same direction as your inclined orbit), right at the AN or DN.  Then, you coast up to that Ap, and there you do your inclination change.  It's relatively cheap in terms of dV, because your orbital velocity at Ap is low, so inclination changes are easy.  Now you're in an equatorial orbit, so you just coast back down to Pe and do the remaining 400 m/s of your burn to eject to Kerbin.

If you're positioned somewhere other than one of the above two, then it's less ideal, but if you apply the above techniques to whichever one is closer, you can probably do a bit better than if you had to do an actual plane change.

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As a possible alternative to arriving equatorial, consider just correcting so AN/DN match Pe, even if that increases inclination slightly.

If you are capturing, you are already making a large dV burn at Pe. Due to non-linear trigonometric behavior adding a normal component of a few hundred m/s costs less than tens of m/s! This technique also translates nicely into rendezvous on arrival maneuvers as you gain proficiency.

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correcting  inclination at the far edge of eve soi isnt all that bad, especially ifyou can get your pe close to you an/dn.

but you can also do it at your relative an/dn while in the suns soi.  if your not going anywhere near one on your journey, your interplanetary transfer is most likely highly inefficient or you launched while exactly at it, without realizing and put yourself on the wrong ejection angle so failed match its inclination from the get go.

 

something i do for moho (yes i know this is quesion is about eve but its the planet i use this trick for) ill put a satelite opposite of kerbin around the sun, with a perfectly matched inclination.  you can them switch to it when you want and select the target you  wanna visit with a craft you wanna launch, it will show you the an/dn relative to it, which will be the same for kerbin as the inclinations are matched.  so you can watch in map view until kerbin is at one of those points to launch.   ofcourse with eve its better to launch during a window but its one way to see your relative inclination  while still around kerbin

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Wow, lots of good stuff to read guys. Here is what I normally do

I have been using the launch window calculator. What I normally do is time warp until a day or two before window, setup a maneuver node according to ejection angle, and input the amount of prograde the launch window suggests. If that doesnt get me an encounter, I tweak the gizmos until I find one. Once I find it, I wait till the node and launch.

I dont mess with AN/DN nodes. I use a mid course burn.

About halfway to the encounter Ill do a mid course correction. With Eve, this means add quite a bit of normal since the enounter will be below it at first. I also try to get equatorial and this is where I cant get anything other than an angled orbit. If I put my Pe on its equator and use prograde/retrograde or radial in/out, my orbit will always be some off angle to the equator.

Alex Moons launch window calculator will tell you to add normal dV to your ejection burn maneuver. I normally dont do that as I get an encounter without having to use normals if i tweak the gizmos. Perhaps this is the issue. Im moving my ejection angle around during tweaking and throwing off the ideal encounter.

Edited by Biggen
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I guess I just realized that if I put my Pe on the equator as mentioned, barely capture, then I could simply burn normal at the Ap to adjust the orbit to equatorial. Im not sure why I wasnt seeing this... Embarrassing...

Edited by Biggen
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When you do that correction maneuver (maybe 1/4 orbit from your target), you can ALWAYS drop the PE on the equator, and it's not hard to eyeball ... just line up your view so your target CB and the sun are in line.  Use normal to put the PE on the equator, use radial and prograde/retrograde to fix altitude, go back to normal to fine-tune, and there you should be.  Your inclination might not be great, but you can easily capture and coast up to AP which has a node.

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