Help getting into minmus sphere of influence?

[CallumButtery]

im trying to send a mapper and a rover to minmus, i have enough fuel to get there but because minmus is on a strange orbit im finding it hard to get into its gravity or orbit, any tips or suggestions or even videos or picture help?

[Vanamonde]

The easiest method is to aim for its orbital height, then look at the map to see if your projected path is going to pass above or below Minmus' orbit. If you're heading below, turn your ship due north (where the gold north line meets the horizon on the navball) and burn, then watch the map and shutdown the engine when you've got an intercept line up. If you're heading above, burn toward the south.

[Ydoow]

What I did, and it's rather full proof once you get a bearing of the directions to burn in, is what follows.

This is full proof, but not the cheapest way to get there

Get your craft's Kerbin orbit similar in circularity and Diameter to Minmus' from a top-down view going in the same direction as Minmus.

So basically, ignore the inclination and match Minmus' orbit exactly the same as you would if you were to do this to the Mun.

Now, get out of that top-down view, and look at Minmus' inclination. Find the points where Minmus intersects your orbit. There should be two points. Er, there has to be.

You want to burn normal (directly upwards) and/or anti-normal (directly downward) just before/after those intersection points.

Following the direction your craft is travelling;

If Minmus' orbit is leading upwards, you want to burn downward just before that point, and/or upward just after that point.

The opposite if the orbit is backwards (I can't remember which way Minmus goes.)

If you mess up and burn the wrong way (or if I told you to burn the wrong way) don't fret.

Just wait until the next intersection point and correct it by doing the opposite of what you just did.

You can burn down and up, or just one. It doesn't matter.

Personally, I only burn upward. It's a hassle to make your ship flip 180 degrees like that.

So I sit with my ship pointing up, and wait for it to 'fly' into the right position to burn.

I think once you try it a few times you'll get a feel for it.

You can definitely practice this orbiting Kerbin if you want.

All this maneuver does is change your inclination.

Do this until your inclination matches Minmus. Well, get it really close.

Now, if you've ever done orbital rendezvous, read no further! Just do that!

If not, I highly suggest looking for the Orbital Rendezvous guide in these forums

You want to burn retrograde (or prograde) very slightly.

Your goal is to make your orbit different, thus causing you to complete an orbit faster/slower than Minmus.

Therefore, Minmus will eventually move closer to you in the orbit.

You MUST take care to be patient.

At some point before Minmus is beneath you, you must readjust your orbit so that you fall into it's sphere of influence.

[CallumButtery]

thanks for the help ill give it a try

[Ziff]

If you figure out the correct time to launch (which is actually pretty easy) , you can even launch at a heading of 84 degrees so your orbit inclination matches Minmus right from the start. Then you just need a single correctly timed injection burn to reach Minmus. I can give you instructions if you like.

[Thobewill10]

I'm not the questioner, but timing is not my strong suit. Would you mind explaining?

[olex]

If you launch at the moment when Minmus is crossing the ecliptic plane in its orbit, and Kerbin is rotated so that your ship at the KSC, Kerbin core and Minmus are roughly aligned with each other, you can launch into a 84° heading orbit, and it will match Minmus' orbital inclination.

[bsalis]

This is what I do...

1. Launch into a circular easterly (90 degree) orbit

2. I then use Map View to see where the ascending and descending nodes are for Minmus. Zoom out and look for the intersection.

(see this about what I mean there)

3. I do a 6 degree inclination change at either of the nodes. So, at the ascending node, it's a burn starting when pointing north, which is north on the nav ball, between the green markers, and where the blue and brown hemispheres meet. As the inclination changes, slide along the blue-brown border to stay between the green markers. For descending node, it's a south burn. To stop at 6 degrees use, map view and stop the burn when your blue orbit line matches the purple Minmus one... or use MechJeb that tells you your inclination.

4. Using map view again, wait until Minmus rise (same as getting to the Mun).

5. Do a transfer burn so that your Ap is at the Minmus orbit line, or you see the SOI capture.

6. I then tweak the trajectory as needed, sometimes en-route. Some SOI fishing may be required.

7. Profit

Edited August 16, 2012 by bsalis

[Ziff]

I'm not the questioner, but timing is not my strong suit. Would you mind explaining?

Sure. When you are on the launchpad go into map view. Zoom in and center the map over KSC and position the camera so Kerbin's orbit looks flat, like this.

[

Then, zoom out and look at where the plane of Minmus is. [Edit] Obviously it's the purple orbit, don't mind that bit of space debris.

[

You can see above it isn't lined up flat, so if you were to launch now at 84 degrees, you would not match it's plane. But if you time warp a little bit..

If you launch now at a heading of 84 degrees, or inclination of 6 degrees if you are using MechJeb, you will be on the same plane as Minmus. Just make sure Minmus's plane matches the photo. If it is positioned the other way, going from top left to bottom right, your plane will be opposite Minmus's. Ideally you want to launch just before Minmus's plane flattens out, rather than just after, for the best timing.

I've tested this repeatedly with some small 1man craft and found the fuel difference to be negligible. On my test craft after getting to minmus with an inclination change, avg fuel left was 551.7L, by using the inclined orbit method, avg left was 557.2. Fuel was read at the moment there was a Minmus encounter.

Edit: Also, you can then wait for Minmus rise to do your injection burn as well. It's just harder to see on the mapview. It helps to zoom the map in and out a few times so Minmus keeps popping up on the map.

Edited August 16, 2012 by Ziff

[Vanamonde]

Ziff put a lot of work into that post. Somebody give him a ref point, huh? (I would, but I gave you one a couple of days ago and it's telling me it's too soon to do it again, or some nonsense like that.)