Lining up a shot to Minmus using math and calculation

[Fifflethecat]

I\'ve been looking for a way to get to Minmus for a while now and most of the time people have some sort of 'Mcgyver' way of accomplishing this but, what formulas and calculations can give me an exact answer on when and where I would need to burn in order to get caught by the gravitational influence of Minmus?

Also, any other useful formulas would be nice.

[Crass]

I don\'t have any precise method of landing on the Minmus, but I have a system that works well enough for me. I basically boost up into an elliptical orbit matching the height of Minmus. I\'ve even gotten lucky a few times and have been able to get the Mun to slingshot me up to that orbit for a much more fuel efficient ride. Once my apoapsis is even with Minmus\'s orbit, I do an alignment maneuver to match its orbital inclination. There is a simple way of doing it by basically aligning the orbital lines in the map view so they both look like solid lines, and then burning either north or south at the point where the two lines intersect. Sorry I\'m bad at describing this. Anyways once the apoapsis is matched, the inclination is matched, I simply burn prograde at apoapsis until the patched conics show me entering the SOI of Minmus.

This is by no means the most fuel efficient, or smartest way of doing it. I have a tendency of overbuilding my rockets, so fuel isn\'t my biggest concern. I\'ve recently been playing around with a rover/lander concept using stock parts, that so far have had 100% success when landing on the frozen 'lakes' (slopey areas ehh... not so much). http://i.imgur.com/rzOvd.jpg

Anyways sorry this isn\'t the most technical answer, but getting these basic steps down have allowed me to land several ships on Minmus quickly with ease. If this isn\'t the info your looking for hopefully someone else will post with a more intelligent method, I too am very curious to see what others have come up with!

[maltesh]

The basics of the standard Mun intercept (Get into a low, eastward equatorial orbit, wait until the Mun rises, then burn prograde until your apoapsis hit the distance of your target), for the most part, works as well for Minmus as it does for the Mun,. Both will sweep through about a 63-degree angle in the time it takes you to Hohmann transfer out to their orbit.

The difference with Minmus is that its six-degree orbital inclination means that you\'re going to miss it if that\'s all you do, however.

What an actual Space Agency would do is wait until one of the orbital nodes of Minmus passes over KSC and launch directly into a six-degree inclined orbit from there.

What I do (because I can\'t be waiting around the scant three hours on what\'s generally a two-day trip) is launch into an equatorial orbit, wait for Minmus to rise, burn to put my apoapsis out at the 46,400 km distance of Minmus.... Then I coast out to 20,000 km and do a course correction, when I\'m moving much slower, and it\'s less fuel-expensive.

IDepending on whether my apoapsis is above or below Minmus\' orbit, I burn in the antinormal (Southish and parallel to the surface of Kerbin if you\'re not using MechJeb) or the Normal direction (Northish and paralell to the surface of Kerbin) to put my apoapsis on Minmus\' orbit.

If that doesn\'t result in an intercept, I then start 'feeling around' on the orbit of Minmus, to move my apoapsis back and forth on the orbit until I find an intercept point; Burning radially or anti-radially to move my line of apsides, and prograde or retrograde to pull in or push out my apoapsis and keep it on the Minmal orbit. It usually doesn\'t take me very long to find an intercept juncture.

[duckunlimited2]

I made one of the earliest guide on rendezvous way back before persistence was implemented. It works on most circular orbits and its my main method for rendezvous. Actually, I just used it last night to get a satellite to minmus. Its an old thread though so don\'t go resurrecting it.

Notes: Its alot better when you do the transfer burn a tiny bit later than mentioned in the guide. Its better because if you do miss minmus, its easier to wait for minmus to catch up to you than you trying to speed up your craft to minmus. (less fuel and less hassle)

Also your calculating ORBITAL RADIUS, NOT ALTITUDE. Make sure you add kerbin\'s radius (600,000m) to the altitude to get orbital radius. I will make your life easier and tell you that your pre-transfer burn orbital altitude is 29,010,000m if you want to get to minmus.

Good luck and here\'s the link: http://kerbalspaceprogram.com/forum/index.php?topic=7138.0

[Endeavour]

Same way you would go to the Mun, with a little refinement. When you see it rise, burn prograde until your orbit touches the orbit of Minmus. About halfway there, turn either normal or anti-normal and burn until the plane matches. Then burn either prograde or retrograde until patched conics says you meet.

[Koschei]

I suggest not making plane corrections mid-flight, but watch your navball at launch and point slightly (6°) below the 90° (East) mark you launch to the Mun with when you do your gravity turn. It is more fuel efficient and simpler.

[maltesh]

I suggest not making plane corrections mid-flight, but watch your navball at launch and point slightly (6°) below the 90° (East) mark you launch to the Mun with when you do your gravity turn. It is more fuel efficient and simpler.

That only works if you\'ve timed your launch window so that you\'re launching near the time that Minmus\' descending node is overhead. If you didn\'t time the launch window, you\'ll likely still have to make a course correction. If you just launch into a 6-degree inclined orbit in this fashion, without paying attention to the nodes, you stand a 50% chance of having to make a bigger mid-course correction than if you\'d launched equatorially.

[haltux]

There is an alternative approach that works fine for Minmus.

Take a circular orbit around Kerbin, similar to the one of Minmus, just a bit smaller. Eventually you catch up with it.

You can improve this technic by taking a significantly smaller orbit to catch up Minmus faster, and enlarge it when you get closer to Minmus (spiral trajectory)

Of course it makes you waste a little bit of energy and a lot of time. But at least it works 100% times and does not require a hasardeous and not very natural 'trick' like the minmusrise one.

It works also for Mun, I actually went there like that the first time. But it makes less sense considering that any elliptic orbit which brings you far enough will bring you tu Mun anyway in three or four orbits at most.

[Koschei]

That only works if you\'ve timed your launch window so that you\'re launching near the time that Minmus\' descending node is overhead. If you didn\'t time the launch window, you\'ll likely still have to make a course correction. If you just launch into a 6-degree inclined orbit in this fashion, without paying attention to the nodes, you stand a 50% chance of having to make a bigger mid-course correction than if you\'d launched equatorially.

Didn\'t think about that... Guess you just have to time it right. Always has worked for me, however.

[LambdaCactus]

What I do is plane change from a Kerbin equatorial orbit. It\'s pretty accurate and doesn\'t take much fuel. Here\'s how:

1. Get into a circular equatorial orbit

2. Focusing the map view on your craft, zoom out until both the front and back lines of the moon orbit are in your view. Line them up so you\'re looking at the moon\'s orbit 'edge-on'. You should see Kerbin in the middle, and a horizontal white line going across it for the moon\'s orbit.

3. Turn your view until the Minmus orbital plane crosses behind Kerbin (You may need to zoom out a bit more). You are now looking directly at the intersection of the two planes.

4. Check which way you need to burn: at your craft\'s next crossing of the intersection, you will either need to burn north or south to change the angle. You can orient your craft to put the navball on the horizon at 0° north or 180° south and lock it there. You can set this up ahead of time: unlike when pointing prograde in orbit, these points on the navball won\'t move, they\'ll just rotate about your ship\'s axis.

5. Zoom in until you can see the sphere of Kerbin fill the top and bottom of the screen. If you\'ve focused the map view on your craft, Kerbin will move across your view from side to side while your craft stays centered. You\'ll know you\'re at the intersection when the space on either side of Kerbin is equal.

6. When you reach the intersection, burn full power. You\'ll have to zoom out to see the Minmus orbit, and zoom back in to overlay your craft orbit. Check a few times until your orbits look like the same angle. Cut the engines.

As for exactly when to start your transfer burn to Minmus, I\'m not sure. I can usually get it pretty close, but I still have to sweep around with small radial burns mid-course until I find an intercept.