Intercept Predictor

[locustgate]

Is there a program to predict an intercept, I have been trying to get to minimus but after 10 minutes of rotating and increasing/decreasing the burn I give up .

[Zylark]

There is always MechJeb. Get your craft to orbit, then select Minmus as target. Next up go to MechJebs Maneuver Planner, select Match Planes with target and then create and execute. Once that is all done, select Hohmanns Transfer to Target. This time though, just select create, not create and execute.

OK, once the maneuver node is created, select it and pull out the radial (blue) node a bit and adjust the prograde (green) marker a bit. You want to jiggle about with the blue and green adjusters until you get a good Pe (around 50km or thereabout) for your intercept of Minmus. Once you're happy, hit the execute next maneuver node button.

Once in Minmus Sphere of Influence, select the Circularize tool of MJ. Select to create node at next Pe. Hit Create and Execute. A little while later you should be done and in a nice orbit around Minmus.

After seeing how MJ do it a few times, it gets pretty easy doing it manually. Though I must admit to my sins, I still let MJ do the plane change and circularization bit. The transfer burn I set up manually however, as doing it directly is faster than fiddling with a MJ created maneuver node.

Edited November 14, 2014 by Zylark

[AlexinTokyo]

Minmus is in an inclined orbit around Kerbin, so it's possible the reason you can't get an intercept is that you're passing above or below its orbit.

The easy (not necessarily the most efficient) method to account for this is:

1. Get into your LKO parking orbit.
   
2. Set Minmus as your target - you should see two yellow triangles on your orbit, marked 'AN' and 'DN'. These are the ascending and descending nodes, where your orbital plane intersects with that of Minmus. If you mouse over them, you will be able to see the angle between the two planes (about 6 degrees for Minmus)
   
3. At one of the nodes (doesn't matter which) place a maneuver node. Then use the purple node 'arms' (normal and anti-normal) to create a maneuver so that the angle between your orbital plane and Minmus' drops to 0 (the nodes will move around the orbit - don't worry about this).
   
4. Perform the planned maneuver.
   
5. You should now be in the same orbital plane as Minmus, and can burn prograde (at the appropriate time) to get an intercept, just like going to the Mun.
   

Hope this helps

[Jovus]

Another, more efficient way: in your parking orbit, put out a maneuver node and use it to boost your orbit to roughly where you think you ought to be to be in the neighborhood of Minimus when it gets there. (You'll want your apoapsis to be above 46,000,000m, but not too far above.) Then, on that predicted orbit, drop a second maneuver node - doesn't matter where, but for efficiency's sake it should probably be somewhere beyond the orbit of the Mun and not too close to the orbit of Minimus. Then, on that second maneuver node, play with the radial burn indicators. Fairly quickly you should get a close approach marker. If it's not where you like, you can drag that first node around your parking orbit. (This may require some readjustment of the second node as well.

[Starman4308]

Another suggestion is to try to immediately match the plane of Minmus's orbit. What you do is wait until you can draw a line straight out from the space center which crosses Minmus's orbit (you are directly under the orbit), and launch six degrees away from east (either north or south, depending on whether you are under the ascending or descending node). If you do it right, you wind up in almost the right inclination, which minimizes the amount of effort you spend on the plane change.

The easy way to do it from there is to create a node at ascending/descending node to exactly match planes, and then do your Hohmann transfer, but the more efficient way is usually to transfer first, match inclinations second. The reason that works is that plane changes are easiest at low velocity, so if you have an ascending/descending node halfway out in the transfer, when your rocket is at a much lower velocity than LKO, your plane change will be more efficient. The only exception is if your AN/DN will be immediately after the transfer, when you still have a lot of velocity from the transfer.

EDIT: An extreme, illustrative example of plane changes: I once launched a rocket into Munar orbit, but accidentally sent it into the opposite direction from the rest of my orbital flotilla. A direct 180 degree plane change in low Mun orbit (reversing the orbit) would have cost more dV than I had remaining. However, I discovered that a bi-elliptic transfer would work: I raised apoapsis almost to Munar escape, reversed my orbit at apoapsis, and returned to low Munar orbit on a dV budget which would have been just barely enough to cancel my velocity in low Mun orbit.

Edited November 14, 2014 by Starman4308

[locustgate]

I'm asking more along the lines of http://ksp.olex.biz/, but one that works with moons.

[Red Iron Crown]

There's not really a need for a transfer calculator for going from LKO to the Mun or Minmus as there's an efficient transfer opportunity every orbit.

If you're doing Mun-Minmus or Minmus-Mun then transfer windows become relevant, you can use Alexmoon's excellent calculator to plan them. Both the MechJeb and Transfer Window Planner mods incorporate similar functionality into the game itself.

[Geschosskopf]

Here's the quick-and-dirty, no-thought-required method of getting a Minmus intercept. The idea is to arrive at Minmus when it's at or near its AN or DN with Kerbin's equatorial plane. That way, you don't have to worry about doing a plane change to get an encounter.

1. Launch into an equatorial LKO as normal.

2. Set Minmus as the target so you get the AN and DN markers on the map.

3. Create your maneuver node at whichever of the AN or DN markers is behind the current position of Minmus.

4. Pull on the prograde node handle until you get the closest approach markers, then fine-tune the amount of prograde until you get an intercept. That's really all there is to it.

What happens most of the time using this method is that your burn puts your Ap out beyond the orbit of Minmus and you get your encounter after you pass Ap on your way back towards Kerbin. Thus, by varying the size of the burn, you change your Ap, which changes the time of when your ship crosses the orbit of Minmus. So what you're really doing when you're pulling on the prograde handle is changing the timing so that your ship gets to the crossing point at the same time as Minmus.

This is not the most efficient way to get to Minmus because your Ap will be out beyond Minmus instead of right at it. However, the difference is insignificant. You're talking a difference usually of less than 50m/s, which isn't enough to make or break you. You'll also have to burn a tiny bit harder to capture at Minmus but again, not enough to worry about.

But that's why this is the quick-and-dirty method. You get the "quick" in having a sure-fire, simple, no-brainer method of getting a Minmus intercept. And you have the "dirty" in this requiring slightly more fuel than if you'd used a more brain-intensive method.

[LethalDose]

Another method that should work, but may take a while is as such (I'm gonna crib the first few steps from Geschosskopf's post above):

1. Launch into an equatorial LKO as normal.
   
2. Set Minmus as the target so you get the AN and DN markers on the map.
   
3. Create your maneuver node at whichever of the AN or DN markers is behind the current position of Minmus.
   
4. Pull prograde until your AP is between 46 and 47 Mm.
   
5. Create a second maneuver node up at the Ap, and pull prograde again until you get an intercept.
   

You can also right click on the maneuver node to bring up some other options, specifically the + and - buttons that let you add or subtract orbits before the node.

This really won't get an intercept quickly as you may be making a few orbits, but it's not really tricky. It's also a good time to learn those add/subtract orbits buttons. If you're you're feeling really cheeky, you can also try to adjust your inclination while you're up there.