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# ascending nodes

## Question

I took on a contract that wanted me to put a new probe into an orbit with certain parameters, and I have made it most of the way, but I don,t know how to change my ascending node. Help is much needed!!

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30 minutes ago, the one who actually tried said:

I took on a contract that wanted me to put a new probe into an orbit with certain parameters, and I have made it most of the way, but I don,t know how to change my ascending node. Help is much needed!!

Hello, and welcome to the forums!

The "ascending node" and "descending node" mark the places where the plane of your orbit crosses the plane of the target orbit.  The way you alter it is to thrust in the or direction when you are at the right spot in your orbit.  Specifically, you want to thrust when you're at the descending node, or when you're at the ascending node.

If you mouse-over the AN/DN marker, it will show you an angle in degrees.  That tells you how much the plane of your orbit is "tipped" relative to the target orbit.  You want this number to be zero in order to match the orbit.  So, the way you do this is to wait until your ship is located at the AN or the DN, and then thrust appropriately.  As you thrust, you can watch the number get smaller.  When it hits zero, you've matched planes.

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Posted (edited)

Hi there and welcome to the KSP forums!

Do you mean the contract is asking you to put your ascending node in a certain place around the planet? Or do you mean you don't know how to change the ascending node of your own orbit relative to your target orbit?

The ascending and descending nodes are just the points where your orbit crosses the plane of another. That could either be relative to a target orbit, or relative the equator of a planet or moon. They define the relative inclination of your orbit.

If your contract is asking you to put the longitude of ascending node in a certain place then don't worry, this is just where the orbit crosses the equator of the planet or moon you are orbiting. As soon as you match the target orbit's apoapsis, periapsis, inclination and direction of travel then your ascending node will just end up in the right place without you needing to do anything else. It's an automatic side effect of matching up with the target orbit. So if the line of your orbit overlaps the target orbit relatively closely then you've already done all you need to do.

If you instead need to know how to move the ascending node around to another point along your orbit then it's a little more complicated. The short answer is that it's usually neither efficient nor practical to do so in most situations. It can be done by burning towards the normal or anti-normal direction when you are somewhere between the ascending and descending nodes, but I wouldn't recommend this. Unless you have an excess of fuel and are in a real hurry it's usually very wasteful except for fine tuning minor adjustments.

The best option, as the others here have said, is to wait until you come to the ascending or descending node and burn in the normal or anti-normal directions (upwards or downwards relative to your orbit direction) until you match the inclination of your plane to your target's plane. And then after you've done that you can burn prograde or retrograde at your apoapsis or periapsis to get the inside and outside extremes of your orbit to match up with the target orbit.

Edited by HvP

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Two small additions to Snark's post:

#1: You also have equatorial ascending/descending nodes, which mark where your orbit crosses over the equator of the body you are orbiting. Don't confuse those with the ascending/descending nodes of your orbit relative to a target orbit.

#2: It's most efficient to change planes at the node closest to apoapsis: this is because you are going slower at apoapsis.

For sufficiently large plane changes (of about 85 degrees), this effect becomes so pronounced that a bi-elliptic transfer is the most efficient way to make a plane change. For a bi-elliptic, you burn prograde at one node (preferably the lower-altitude node) until you are almost at escape velocity. Then, you can make a plane change near apoapsis, and then burn retrograde at periapsis to bring your altitude back down again, and you can overall spend less delta-V with this maneuver.

Again, it's only for very large plane changes of ~85 degrees or more that bi-elliptic tends to beat "just make the plane change wherever".

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If your orbits kinda look like this vs. the objective because of some timing issues with the burn:

Then with a bit of experimenting, you can adjust your orbit using a combination of  or Radial In (how do you get that to show up?) and  /   to jog the Ap/Pe along. Works well for really large orbits when you can't be bothered to wait a hours/days to shift things about, only to mess up again because of minor timing issues with the burn.

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1 hour ago, Weywot8 said:

Radial In (how do you get that to show up?)

Longer "how do I figure out this kind of thing?" answer in spoiler section, for anyone who's interested.

Spoiler

If you're ever trying to figure out "how do I insert one of those little KSP specific emoji such as ?", you can get the forum to show you all the available ones and how to type them-- it's just kinda hidden and you need to know where to look.  Here's how you can see them all:

1. Click the emoji button on the toolbar at the top of the post (it's the little smiley-face button, in between the <> code button and the spoiler-section button).
2. When the dialog pops up, it shows a bunch of emoticons, but not all of them (yeah, I know, it's unnecessarily silly).  So click the "Categories" drop-down in the top right corner of the dialog, then pick "Emoticons" from the list.
3. That will show you the full list.  You can click on any one of them to insert it in your post, or just mouse-over to see what you need to type to have it get automagically inserted.