Adjusting for Kerbin rotation when landing at KSC, a how-to.

[Cal'Mihe]

Hi all, as I was watching the 0.21 KSP-TV special, I noted that Yaghir had some issues estimating on the fly the rotation of Kerbin in order to land directly at KSC. So I thought I'd show the little solution I have put in place if others want to apply something similar in their games.

I know there are probably mods that do this, but I prefeered to find a stock solution

As Kerbin is on a 6 hour rotation, we're in the fortunate situation that every hour Kerbin will rotate 60 degrees. So if I want to land at KSC and I'm precisely 2 hours away from touching down, then I should try to make my touch-down point 120 degrees East of KSC. In that period of time, Kerbin will rotate so that KSC will be directly at the landing point when the space-craft gets there.

If you use a mod that tells you the coordinates of a landing site, then you can simply calculate the difference of the coordinates, and ensure that you are that many minutes worth of degrees away from landing.

Alternatively you can put in place a set of beacons, to aid you in eyeballing it:

Here I have put in place 6 beacons at the equator around Kerbin, with 60 degrees between them. One of them is located right at KSC.

As the distance between one beacon to the next represents one hours worth of rotation, I can use that to aid me in eyeballing where to come down for landing to be as close as possible to KSC. An example:

Here is Merrie Kerman, comming back from a trip to the Mun. As he has heard that the canteen is serving his favorite dish today, he really wants to go directly home and not having to wait for the recovery ship to pick him up half-way around the World.

To that end the manuver node making the transfeer from Mun orbit is tweaked slightly, so that he will make a touchdown close to Beacon West 120, meaning the beacon 240 degrees (4 hours) away from KSC. That path will take him 3 hours and 53 minutes, checked by placing a manuver node on the estimated trajectory and seeing at what time it touches ground. This means Merrie will land close to KSCs canteen, and his spaceplane can glide the rest of the way to the runway.

If I find that I'm slightly off, then the trajectory can be adjusted halfway though. Its also much easier to fine-tune by eye the off-set needed for (for instance) 15 or 30 minutes worth of rotation when I have these navigational aids.

Lastly, here is a shot at one of the beacons, they could be anything really, essentially just a piece of debris will do, I just thought I'd make something resembling a beacon

For reference, if you want to put a series of beacons up like this, or calculate it directly, then your beacons will need to be at the following longitude coordinates (as measured by Kerbal Engineer):

Beacon 0 (KSC) : -74.575

Beacon East 60 : -14.575

Beacon East 120 : 45.425

Beacon 180 : 105.425

Beacon West 120 : 165.425

Beacon West 60 : -134.575

Or these if you're using the coordinates as pr the tracking station:

Beacon 0 (KSC) : 74.57 W

Beacon East 60 : 14.57 W

Beacon East 120 : 45.42 E

Beacon 180 : 105.42 E

Beacon West 120 : 194.35 W

Beacon West 60 : 134.57 W

Note that it looks like the zero-point for the tracking station coordinates are off, as no longitude coordinate should be above 180.

The principle can be used for all the other planets as well, such as a base on Duna, just look up the rotational period and put down beacons accordingly

[Tw1]

That's a good strategy. I take it flags don't work because some will need to be in water?

[Cal'Mihe]

Precisely, beacons East 60 and West 120 need to be in the water, though reasonably close to shorelines both of them.

What I did was air-drop the beacons down on a small rover platform as close to the coordinates as possible, and then drive them into the precise position.

For the naval beacons I used a small set of rocket motors on the platform to enable them to move a bit on the water after they had come down by parachute.

[Javster]

Very helpful. Would these coords work w/ hyperedit?