Determine approach from far away.

[Dortmunder]

Hey all.

I'm not new to KSP or anything, but I've noticed recently(doing more long journeys like Jool etc.) that I've been coming in on the wrong side of the planet/moon I am aiming for.

How do you determine what side of the planet/moon you're coming in on easily? For instance, come in around Jool to aerobrake and get an encounter with Vall. Fine tune the orbital height. But when you enter the SoI of Vall, you're coming in around the wrong side. Wasting fuel to gain orbit.

I can generally determine if I'm coming in on the right side, but sometimes I'm just not sure

[UmbralRaptor]

The big thing is to do a mid-course correction. You can partially check on where you're going by cycling the map view (tab, shift+tab).

[Temstar]

When you slingshot around a planet or moon prograde, the momentum of the planet/moon adds a certain velocity to your craft, depending on how wide of a angle you are deflected by. Likewise a retrograde sling means you slow down your craft relative to your primary and make that planet/moon orbit the primary a tiny tiny bit faster. The higher the gravity of the planet/moon that's deflecting you the wider your deflection angle is, hence why Jool/Jupiter is used for interstellar probes as they can add a huge amount of velocity to your craft for free.

If we spin that same logic around 180 degrees, it means we are able to tell if your slingshot is prograde or retrograde by looking at the effect it has on your orbit. Assuming you have a low PE around your target so that gravitational slingshot effects come into play, look at the new orbit that you will enter into after you leave your target's SOI:

• If your new orbit has a higher AP than your current orbit, then you are slinging around the target prograde
  
• If your new orbit has a lower PE than your current orbit, then you are slinging around the target retrograde
  

[Specialist290]

This post has a couple of methods you can use to figure out what your approach is going to look like before you get inside the SoI of your target. In particular, I've found the second one to be quite helpful myself as a way to "eyeball" it quickly.

Another thing you might want to look into is changing the patched conic drawing mode the game uses. You can do that by changing the number in the line "CONIC_PATCH_DRAW_MODE = 3" in the settings.cfg file to whatever mode you want, or you could download something like PreciseNode that lets you toggle between draw modes while still inside the game.

[Vector]

If we spin that same logic around 180 degrees, it means we are able to tell if your slingshot is prograde or retrograde by looking at the effect it has on your orbit. Assuming you have a low PE around your target so that gravitational slingshot effects come into play, look at the new orbit that you will enter into after you leave your target's SOI:

• If your new orbit has a higher AP than your current orbit, then you are slinging around the target prograde
  
• If your new orbit has a lower PE than your current orbit, then you are slinging around the target retrograde
  

Keep in mind things are reversed when going from higher-to-lower orbits (say Kerbin to Eve) as opposed to lower-to-higher orbits (Kerbin to Mun or Kerbin to Duna). I made this error myself and ended up going the wrong way even though I thought I was going to end up prograde.

From lower-to-higher orbits with Hohmann transfer (i.e. intersect is tangent to target's orbit), you are going slow and the target is going fast, so the target is approaching you from behind. Prograde and retrograde can both potentially sling you forward, but prograde will sling you outward while retrograde will sling you inward. Look to see which way your orbit is going after the encounter, if it has bent to the left or bent to the right.

For higher-to-lower orbits like Kerbin to Eve, the situation is reversed because you are going fast and the target is going slow. You are approaching the target from behind. Prograde or retrograde can both slow you, but prograde will sling you inward while retrograde will sling you outward.

If your intersection is not tangent to the target's orbit, then you have some radial velocity which makes it more complicated because you very likely have both radial and tangential velocity. For the radial component alone, if you are moving radially outward relative to your target, then prograde around your target (say Mun) will send you prograde around the parent body (Kerbin), meaning higher Kerbin orbit around after the encounter. Retrograde around your target will send you retrograde around the parent body.

But again if you are going from a higher to lower orbit, moving radially inward, then the situation is reversed. Prograde around the target will send you retrograde around the parent body, and retrograde around the target will send you prograde around the parent body.

I believe there is also a way to see directly using settings to change how conics are rendered, but I haven't ever used it.

[Sirine]

http://forum.kerbalspaceprogram.com/showthread.php/48342-How-to-warp-into-Eve-Gravity-Influence-in-the-correct-angle/?page=1 check this out.

[Awaras]

Also, I believe that KSP now lets you focus on the intercept point by double clicking it. Just zoom in on the intercept point and fine-tune your approach when you are about half way there.

[Kasuha]

Also, I believe that KSP now lets you focus on the intercept point by double clicking it. Just zoom in on the intercept point and fine-tune your approach when you are about half way there.

Didn't work for me when I tried it. But again, I have sometimes trouble highlighting apoapsis/periapsis as when I click on them, a menu appears instead for something unrelated that happens to be within clicking distance of the marker. Most often the "add maneuver" menu.

By the way for apoapsis/periapsis it's single click, not double click.

I wish they did things in a unified way. E.g. I right-click somewhere, and menu appears, containing "Highlight AP marker/Highlight DN marker/Highlight intersection marker/Select XYZ as target/Add maneuver" and lets me choose what I want to do at that point.

[Awaras]

Didn't work for me when I tried it. But again, I have sometimes trouble highlighting apoapsis/periapsis as when I click on them, a menu appears instead for something unrelated that happens to be within clicking distance of the marker. Most often the "add maneuver" menu.

By the way for apoapsis/periapsis it's single click, not double click.

I wish they did things in a unified way. E.g. I right-click somewhere, and menu appears, containing "Highlight AP marker/Highlight DN marker/Highlight intersection marker/Select XYZ as target/Add maneuver" and lets me choose what I want to do at that point.

Right, sorry, it lets you focus on the maneuver node, but not on the intercept point around your target... I was sure I read somewhere that you could do that but it looks like I was wrong... :/

Conic patch draw mode 0 is your best bet then. It draws the intercept path around the actual target body instead of it's ghost image. That lets you focus on the target body, zoom in really close and fine tune your approach. The maneuver node improvement mod lets you change the patched conic mode on the fly, and gives you more precise control of the maneuver node.

[John FX]

Didn't work for me when I tried it. But again, I have sometimes trouble highlighting apoapsis/periapsis as when I click on them, a menu appears instead for something unrelated that happens to be within clicking distance of the marker. Most often the "add maneuver" menu.

By the way for apoapsis/periapsis it's single click, not double click.

I wish they did things in a unified way. E.g. I right-click somewhere, and menu appears, containing "Highlight AP marker/Highlight DN marker/Highlight intersection marker/Select XYZ as target/Add maneuver" and lets me choose what I want to do at that point.

I have been wanting for a while now that they would implement some way that, when I click on a bundle of stuff in the map mode, it presents me with a list so I can at least select the craft/body/maneuver node I want.

It seems so basic to have this.

[Frederf]

Once you get an encounter you could focus on the destination body if you have the ability to change the conic draw mode. I also didn't know about tab/shift-tab. Thanks!