How to turn this into an orbit?

[Qwotty]

This is really bothering me! I can't for the life figure out how to get this into an orbit, mostly because of how inclined it is.

[Tortoise]

All you have to do is timewarp to the periapsis and burn retrograde until it turns into an orbit

[allmhuran]

Correct me if I'm wrong, but it looks like you've entered Jool's SOI from solar orbit and want to turn that from a Jool flyby into a Jool orbit.

I suspect you would also prefer your Jool orbit to be on a similar plane as the orbits of some of the moons. But for right now, let's ignore this part to focus on the first question. I'll come back to this afterwards.

So, to turn your Jool fly-by into a Jool orbit, you have to slow down relative to Jool. Since you've come in from a solar orbit you're going to leave again at the same relative speed unless you burn to reduce that speed.

There are two ways to do this with Jool: One way is to fly past Jool at very low altitude... so low that you dip into its atmosphere and the drag from the atmopshere slows you down. This would be an "aerocapture". But if I've interpreted your situation correctly, that's clearly out of the question... you'll be passing Jool near the edge of it's sphere of influence and, of course, nowhere near the atmosphere. So from this altitude your only option is to burn. You need to point your chevron at the retrograde indicator and fire up your engines until your fly-by trajectory closes into a captured orbit. Do this as you reach your Jool periapsis.

Now let's look at getting your inclination closer to the plane of the moons. Well, depending on how out-of-plane you currently are, this could cost you quite a lot. But the technique is probably one you're familiar with: after you capture using the retrograde burn from the previous paragraph, set the moon you're interested in as a target, find the ascending or descending node and perform the appropriate burn in the normal minus or normal plus direction.

If you have a save from when you were still in solar orbit a ways out from Jool... say, still a quarter of an orbit or so away from the intercept, you can save some gas. At that distance you can make very small burns that will significantly change your fly-by altitude as well as your inclination when you arrive.

[iFlyAllTheTime]

Seems like the craft is travelling from right to left in that pic before "escaping"

More senior forum members might chime in to correct my noob answer but, click on the periapsis and reduce you velocity, i.e. drag the retrograde marker on the manoeuvre node until you see some sort of ellipse. Looking at the navball, point your craft at a dark blue icon with three lines and a dot in the middle. Execute a burn for the amount of time it specifies just to the right of navball.

Congrats, you're now in an orbit around the body and won't escape it's gravity. You can alter its inclination and/or apoapsis and periapsis once you have an elliptical orbit.

EDIT: The user above me managed to post the reply in the time it took me to type my response.

Edited June 9, 2014 by iFlyAllTheTime
Another user posted a reply during the time I was typing my post

[Qwotty]

Just a heads up, I'm below Jool, very much so.

[allmhuran]

If you're willing to get a little more advanced, I'll add to my previous answer.

You may have read that aerocaptures at a planet can actually be an expensive option if you want to visit a moon or two. Let's think about why this is. In order to aerocapture you have to have a very low periapsis - low enough to dip into the atmosphere. When the aerocapture is complete your periapsis will still, of course, be very low. Your apoapsis, on the other hand, is likely to be quite high. In other words, you'll be in a highly eccentric orbit, which means one that is a very stretched out ellipse.

So why is this often considered expensive? Well, in a very eccentric orbit, you are moving very slowly at apoapsis. A moon at the same altitude would, on the other hand, be moving much more quickly... that's why the moon stays up there instead of falling sharply down the same way you will! And so if you want to then orbit that moon you have to speed up a lot to match it's orbital velocity around the planet. In other words, you pay a lot of delta-v.

But in the case of Jool, that's not actually a big deal. Jool has a *lot* of moons, and you can use them to help you out by performing gravity assists that increase your apoapsis velocity, pulling your periapsis up out of the atmosphere and giving you a more circular orbit. The fact that there are a lot of moons means you have a huge amount of flexibility when you do this, and can pretty much turn any orbit into any other orbit pretty much for free (or at least for a very small delta-v cost) just by gravity assisting from moon to moon.

As such, generally the best method for visiting the moons of Jool is to come in from solar orbit with a very low periapsis and to perform an aerocapture, then bounce around the moons until you get where you're trying to go.

Edited June 9, 2014 by allmhuran

[allmhuran]

Just a heads up, I'm below Jool, very much so.

That's OK as far as capture goes... the technique remains the same: Get to periapsis, and then burn retrograde.

What will happen is that you will end up with a highly inclined orbit... in fact, you'll have an orbit that's closer to going around the poles of Jool instead of around the equator. And you will indeed pay a very high price to turn that into an equatorial orbit. Unfortunately from this position there's no way to make that cheaper. If you decide to capture now by burning retrograde, there's really no way of making that inclination change cheap.

So if you want a more equatorial orbit, and if you have the opportunity, I would definitely recommend loading up a save from when you were still in solar orbit some ways out from Jool, and planning a correction there to bring your approach closer to Jool.

[Qwotty]

Tried burning at perigee to no luck. I have extremely low amounts of torque and a low thrust engine, so burning takes a long time. For some reason, I can burn at prograde just fine and my path lowers, but when I burn at retrograde, however; it won't seem to budge.

[EtherDragon]

It may not be enough to burn only at periapsis, if you have low thrust. You may need to start thrusting now, and just leave the engines on for a long time to slow down sufficiently.

Another option is to use lateral thrust to change your angle of approach, but that will also take some time and you should start "now".

[AlexinTokyo]

Is it possible you are confusing periapsis and pro/retrograde?

To achieve capture, you need to burn retrograde (in the opposite direction to your motion - marked on your navball by a yellow/green ) at your periapsis (the closest point in your orbit to the body you're orbiting - marked on the map by a blue 'home plate' symbol containing the letters 'Pe').

If you have a low thrust-to-weight (actually thrust-to-mass) ratio because of small engines, you will have to start burning well before the actual periapsis in order to decelerate enough to be captured, and it is possible that you simply don't have enough time (or enough fuel) to slow down sufficiently before leaving Jool's SoI.

You can put a maneuver node on the periapsis point (click and select 'Add Maneuver') and then drag the retrograde handle (also marked ) until your predicted (dotted) orbit shows a capture. The display near the navball will then show how long you will need to burn, and how long until the periapsis. If the estimated burn time is longer than twice the time to periapsis you can't make it.

[GoSlash27]

How'sabout this?

Burn retrograde until your orbit just barely closes off. Then ride that orbit to apoapsis on the opposite side. Once there, you should be going so slowly that you can retroburn your orbit to a dead stop for fairly cheap. Then burn East until you establish an aerobraking periapsis on Jool and proceed. It won't be perfectly in the ecliptic plane, but it should be close enough to catch a moon.

Just a thought...

-Slashy

[allmhuran]

Tried burning at perigee to no luck. I have extremely low amounts of torque and a low thrust engine, so burning takes a long time. For some reason, I can burn at prograde just fine and my path lowers, but when I burn at retrograde, however; it won't seem to budge.

Sorry, I can't follow what you are saying here. "Burning at prograde" will just fling you out of Jool's SOI even faster. Perhaps a screenshot when you start the burn so that we can see the navball would help.

[bsalis]

Like others have pointed out... make sure you are actually doing a retrograde burn (ie. ).

In order to turn that highly inclined orbit into an equatorial one. Probably start hunting for a Tylo intercept to swing you around to the right direction.

[Kasuha]

Tried burning at perigee to no luck. I have extremely low amounts of torque and a low thrust engine, so burning takes a long time. For some reason, I can burn at prograde just fine and my path lowers, but when I burn at retrograde, however; it won't seem to budge.

Click on the blue trajectory just below the "Pe" marker. A menu will appear with one item - Add maneuver. click on that button.

Then click and drag the marker which is aimed at your ship and keep pulling it away from the center until your orbit (drawn using dashed line) closes within the SOI.

Then rotate your ship until you get the dark blue marker of the maneuver at the center of your navball. Here I am assuming your thrust is going in the same direction where the center of your navball is which is usually true for most rockets. And then start burning your engines while keeping that marker in the center of your navball.

If this does not work for you, it might be a good idea to post more screenshots such as how does your ship look like or individual steps of your attempts.

[cantab]

Your statement that burning prograde lowered your orbit suggests you're not controlling the ship from a part facing the same way as the engines are burning. You can right-click any command module or probe core and choose "Control from here" and it uses that part for the navball orientation.

Once you have that sorted, you have two main options.

One is to simply burn retrograde when you're near periapsis. Only burn enough to just close your orbit. Then target one of Jool's moons (either the one you plan to visit, or else Laythe or Vall since they both have 0 inclination) so you can see your ascending/descending nodes. Set up a manouevre at whichever node is furthest from Jool, make that manouevre a combination of normal/antinormal and retrograde, so that you correct your orbital inclination and lower your periapsis for either encountering a moon or aerobraking at Jool itself.

The second is to set up a manouvre soon that's a combination of radial and normal, to put your periapsis in Jool's atmosphere for aerobraking and at an angle that will get you an equatorial orbit.

[Qwotty]

Sadly, I wasn't able to get an orbit around Jool, but I was able to farm science.

[nobbers12345]

Learn from this:

As you get farther out or inwards, you will require more and more fuel for braking relative to the planet.

In the case of Jool, you save a lot of delta-v aerobraking into an orbit.

It's the reason why beginners are not advised to go to Moho or Eeloo first, it's a long braking burn, and very costly too because you don't have an atmosphere to slow down with.

Your most efficient bet is to first fix your inclination on a mid-course correction burn by burning Normal or Anti-Normal, and then lower your planet's apoapsis from there using the radials and or pro/retro markers.

[Kryxal]

Too bad, that ... see where else you can go? Oh, and I'll agree with the moon slingshot for inclination change, it takes work but is the most economical in terms of delta-v.

[Qwotty]

I'll stick with the planets that are within a practical distance from Kerbin.

Duna, perhaps?