My semi-simple method for reaching the moons

[Vanamonde]

There have been a lot of questions about how to aim for the moons. The thing is, the exact method can vary depending on how you fly and the characteristics of your ships, so there isn\'t one correct answer. I\'m not an expert, but this is how I figured it out. It works for me, and I hope it will help others.

First, make sure you are orbiting Kerbin on the same plane as the moons, heading east. (That\'s flying compass heading 90 all the way from liftoff to orbit.)

Save the game and, from wherever you happen to be at the time, accelerate your rocket toward the navball eastern horizon (its an easy landmark for consistency of result). Switch to map view and shut the engine down when your apoapsis markers reaches the orbital height of the desired moon. The apoapsis marker then tells you your own personal transit time, to that moon, based on how you fly and how fast your current rocket accelerates (see attached screenshot Time benchmark). You can then do some simple arithmetic to figure out how far the moon will have moved in its orbit by the time you get there: orbital period (from the wiki if you don\'t want to figure it out) divided by your transit time equals the fraction of a circle to aim ahead of the moon\'s current position. Multiply that by 360 to get easier-to-visualize degrees.

For Mun the leading angle is : 138,983/(your transit IN SECONDS)*360degrees.

For Minmus the leading angle is: 1,077,379/(your transit IN SECONDS)*360degrees.

Okay, so how to aim for that angle? First, load your save so that you haven\'t wasted all that rocket fuel and are still in Kerbin orbit.

Hit the tab key to make Kerbin the center of your camera view, then zoom way out looking straight down on the plane of the moon\'s orbit (from north) then rotate until the moon is straight above the planet (Polar view). That is where you would fly to hit the moon if it was not moving, but of course it is. So then rotate the view again until the moon has moved to the right to the desired intercept angle (Corrected aim angle). 'Up' on your computer screen is now the proper direction to fly to intercept the moon. Zoom back in on Kerbin and bring the camera angle back down level to the plane of the orbits (Back to the plane), but keeping that 'up' at the top of the screen. You should now be looking straight at the desired interception point, through the planet (Lined up stars). Wait until your orbiting ship is in the middle of the screen at that burn point, right on that line of ship/Kerbin/intercept point, and hit the throttle. Switch to map view and watch your orbital path climb (Climbing apo), shutting down the engines when the apoapsis marker reaches the orbital height of the target moon.

If you\'re aiming for Mun, this should do the trick and the conics intersection symbols will replace the apoapsis marker as it gets close (Bingo!).

Minmus is trickier, because its orbit can swing above and below the usual plane. You could be lined up properly in the east/west direction and still not see the conics intersection symbols because you\'re too far north/south. The easiest way to fix that is to wait until you\'re partway to Minmus, then look and see if it\'s above or below your path. If it\'s above (Drat! Missed), turn your ship to straight Kerbin-north (on the navball, that\'s where the horizon meets the gold north line at compass heading 360 (Navball north)), turn the engine on low (so you don\'t over-do it), and watch on the map view until the conics intercept symbols appear, then shut down the engine (Sloppy, but adequate). Or if Minmus is below your path, point straight south and do the same thing.

I know there are more elegant ways to do this (especially Minmus with its inclined orbit), but I think this is pretty simple conceptually and can be done from numbers and viewing angles within the game. Anyway, this is how I do it.

Comments? Questions? Vituperation?

Edited August 18, 2012 by Vanamonde

[Themohawkninja]

Am I the only person who doesn\'t orbit Kerbin as a way to get to the Mun?

[BillWiskins]

Am I the only person who doesn\'t orbit Kerbin as a way to get to the Mun?

I\'d like to see anyone get to the Mun without being in some kind of Kerbin orbit...

I\'m just joking. Calm down!

That there is a useful guide, Vanamonde. I shall use it in the future, should I ever be in a rush to get to a moon and not have the time for a lazy old game of \'slightly different orbit catch-up\'.

[AmpsterMan]

I don\'t orbit Kerbin at all when I go for the mun. I think I figured out what the OP did by sheer trial and error; it definately is nice to see all the maths though

[Vanamonde]

Orbiting isn\'t actually required for launch or landing. But since I was trying to make a guide for newbies, I needed a clear place from which to start describing the process.

nice to see all the maths

Ha! There are people on these boards who can REALLY do the math. I just did a little simple geometry.

[cardgame]

Yeah, I just launch straight at them and adjust speed for distance as required. Very simple.

[maltesh]

A bit more geometry.

If your planned apoapsis is much higher than your periapsis, the leading angle winds up being about 63 degrees.

At an altitude of about 100km over Kerbin, the angle between the visual edge of Kerbin and the center of Kerbin is about 59 degrees.

As a result one of the most popular and efficient methods for timing the transfer burn is to get into a low eastward equatorial Kerbin Orbit, wait until the Mun (Or Minmus, if that\'s your target) rises over the edge of Kerbin from your spacecraft\'s viewpoint, and then burn to put your apoapsis on your target\'s orbit.

Since the Mun is close, has a huge SOI, and is equatorial, an intercept is almost guaranteed. Minmus tends to require mid-course correction, as you mention above.

[Vanamonde]

wait until the Mun (Or Minmus, if that\'s your target) rises over the edge of Kerbin

My reservation with that common technique, and I agree that it\'s minor in these circumstances, is that your transit time can vary according to the thrust ratio of your ship and the altitude from which you begin your burn, which of course would alter the degree by which one must lead the target. Are those factors enough to cause a newbie to miss? Not most of the time, it\'s true. I just don\'t like the idea of using the one-size-sort-of-fits all fire-at-moonrise and trusting to slop and luck. That can be wasteful of fuel, which will matter when economics are eventually added to the game. By my suggested method of doing a test run first, the player would get an accurate transit time figure for THAT rocket, altitude, and any steering clumsiness an inexperienced player might bring to the mix. As long as your real burn is as good or as sloppy as the benchmark run, my method should get you where you want to go. You don\'t have to be good, just consistent.

[mrdest21]

I\'ve done the Mun-sets-over-Kerbin (I go westwards and go head on with the Mun) and it rarely misses, if ever, independently of height and speed. My only issue with your method, Vanamonde, is that it kind of feels like cheating

[Vanamonde]

'Cheating' because of loading the save? I get that. But it\'s just a method of measuring the transit time accurately for an individual ship design and player skill. In the game, one can\'t put the ship design on a test rig and measure it directly, and that sort of thing. To me, it\'s less realistc to imagine that a ship crew would risk their multi-million dollar vessel and their lives on, 'Do you see the moon yet Frank, or is that a smudge on the window?' If it makes you feel better, you could pretend that the test-and-load-save is the Kerbals doing a computer simulation before the real burn.