Math to determine time to match plane on launch (at AN/DN)

[westamastaflash]

So I'd like to launch directly into Minmus' orbit (I'm using Kerbin 6.4x, a plane change costs about 300m/s DV in LKO). I'd also be able to launch right into the inclined planes for rendezvous and such.

I have kerbal engineer and I can determine the current angle to the AN/DN of the target using this, but the "time to AN/DN" doesn't work right on Kerbin, I guess it thinks the "orbit" i'm on is straight to the center of Kerbin.

I know Kerbin's rotational velocity (for Kerbin 64k I'm using the 24hr rotation speed, so at the equator at sea level the rotational velocity is 279.25258 m/s).

How can I figure out the location of the Ascending or Descending node of Minmus, so I can compute the time that the KSC will arrive at the Minmus ascending node?

[MockKnizzle]

It's pretty simple to just eyeball it. Zoom out in map mode far enough to see Minmus' orbit, and pull the camera down to look at Kerbin from the side. Then just spin around until Minmus' orbit passes through the center of Kerbin. Put your ship on the pad, and timewarp until KSC passes right under the orbit track, and launch northish/southish as necessary.

[Srpadget]

A reasonably-simple way to keep track of Minmus's nodes, usable in a completely-unmodded stock install (any data-displaying mod like MJ or KER should allow you to do something similar, but more easily).

First, you need something in as perfectly-equatorial an orbit as you can manage. Put something (doesn't matter what, as long as it can do a bit of maneuvering) in low Kerbin orbit. Set Mun as its target, and match planes. Since Mun has a zero-inclination orbit, you now have a reference for Kerbin's equator.

Next, set Minmus as the target of your zero-inclination satellite. Voila--you now have a visual reference to Minmus's node line.

For added fun, send out a Kerbal to plant a flag at the Kerbal Space Center, so you can easily see KSC from the map view also.

To use this: Get ready to launch when Minmus is 90 degrees away from its line of nodes. (Midway between the ascending node and descending node.) This ensures that when you make your transfer orbit along the node line, Minmus will be there when you arrive.

For most rockets, time from launch to LKO is something on the order of 5 minutes (your time may vary, depending on vehicle design and launch trajectory profile; airbreathers take quite a bit longer). So you'll want to launch a few minutes prior to KSC crossing Minmus's node line. To do a direct injection into Minmus-transfer orbit, of course, you'll want to launch at the node line opposite your Minmus-rendezvous point.

As with anything worthwhile (in KSP or in real life), it probably won't work perfectly the first time you try it. Keep at it, it gets easier and more reliable with experience.

[westamastaflash]

First, you need something in as perfectly-equatorial an orbit as you can manage. Put something (doesn't matter what, as long as it can do a bit of maneuvering) in low Kerbin orbit. Set Mun as its target, and match planes. Since Mun has a zero-inclination orbit, you now have a reference for Kerbin's equator.

Now there's something I didn't think of!

If I take it one step further, and put it into Kerbisynchronus orbit almost directly over the KSC, I can figure out how long until the satellite, as well as the KSC, arrives at the burn point to launch directly into to minmus' orbital plane.

I'm so concerned about the time here primarily because I'd like to set up Kerbal Alarm Clock alarms for minmus launch times to set up my minmus MKS colony, but don't want to waste my time time warping (I'm using kerbal construction time so I have a bunch of missions all going at once).

[Srpadget]

Ooh, nice touch! The problem with my "flag at KSC" marker is that there isn't a convenient way to get "time until node" from it except by eyeballing and estimating. You may have just come up with a genuinely USEFUL reason to put a satellite in synchronous orbit (in a game without Remote Tech, Fine Print, etc.)!

[GoSlash27]

^ What srpadget said:

Put something into LKO and use the Mun to zero it's inclination. Now you can use that to target Minmus and project it's AN and DN right onto Kerbin's surface.

Best,

-Slashy