Alshain

How to Launch Directly to Minmus' Inclination

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Alshain    4724
Posted (edited)

Launching to Minmus' inclination is a fairly straightforward process.  Many would have you believe that it requires a lot of math, and technically, it does.  However it is also possible to launch to straight to the proper inclination from the surface of Kerbin without all that fancy math, and we will use the Mun to do it!

Despite this guide being written for Minmus, this process can be used to launch into any inclination of an existing object around Kerbin as long as you know it's inclination.  It can also work around other celestial bodies if you have a craft in orbit with a known 0 degree inclination to take the place of the Mun and your craft is landed on the equator.

What You Need

While it is possible to 'eyeball' this process entirely, it greatly helps to have a mod that shows your current inclination as you ascend.  This will prevent trying to fly and manage a map view at the same time.  It doesn't matter if you want Kerbal Engineer or MechJeb or any other mod, as long as it shows your craft's inclination as you ascend.  This is not required, but highly recommended.

Step 1: Put your vehicle on the launchpad.

Step 2: Enter the map view and set focus on Kerbin.

Step 3: Finding the Mun

We will be using the Mun's orbit as a baseline for this process.  We know that the Mun has a perfect 0 degree inclination around Kerbin and will use that knowledge to our advantage.  Zoom out on the map until you can see the Mun's orbit.  The goal is to have the Mun's orbit appear as a single line, this ensures the 3 dimensional nature of the map does not create an optical illusion.  We want to be looking straight at the equator.  Move your map so that it appears as shown in the correct image below.

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Step 4: Finding Minmus

Our goal now is to find the point at which Minmus crosses the equator.  There will be two times per Kerbal day that this occurs.  To do this, we will do the same thing we did in Step 3.  Adjust the map so that Minmus' orbit appears as a straight line while keeping the Mun's orbit as a straight line as well.  It will be important to note which of the two launch windows we are targeting for our launch, so make a note if the orbit is descending or ascending.

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Step 5: Finding the Launch Window

Once you have your orbits aligned in map view, simply zoom in without moving the map.  Since we focused on Kerbin in step 2, we will zoom in on the center of the planet.  That is where you want your craft to be for launch.  Time warp until your craft icon appears directly in the middle of the planet (it doesn't have to be perfect, just as close as you can get it).  Now you are ready to launch.

Note: Be sure it is in front of the planet, not behind it, since icons show through the planet. 

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Step 6: Launch

Note: the craft depicted does not represent a vehicle capable of reaching Minmus, just orbit.

Minmus' orbital inclination is 6 degrees.  In step 4 we noted whether we were targeting Minmus while ascending or descending.  As you launch, if you are launching to Minmus' ascending trajectory, you will aim just below the 90 degree mark on the navball (Heading 84 degrees).  If you are launching to Minmus' descending trajectory, you will aim just above the 90 degree mark on the navball (Heading 96 degrees).  If using an inclination mod, adjust your heading so that your final inclination is 6 degrees (some mods may depict this as -6 degrees for one of the two launch windows).

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Conclusion:

If you have followed along correctly at this stage you will find yourself in an orbit that very closely matches Minmus.  It should be close enough for Minmus' gravity to take over if you attempt an encounter without making any further inclination adjustments.

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Edited by Alshain

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Pretty good, I approve. Quick note on the use of mods, it's entirely optional. As you pointed out yourself, inclination does correspond to either "just above" or "just below" the 90 degrees line on the NavBall. That's not a coincidence, that's because the NavBall does provide a decently accurate idea of your heading, which does translate to inclination. It even shows numbers. "Just above" and "just below" should then be something along the lines of 95-96 degrees heading or 85-84 straight from the launch pad.

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Alshain    4724

@Ohm is Futile You are absolutely correct, however given that the stock navball texture is less than ideal and only has a meridian every 45 degrees, I wanted to keep the tutorial as simple as possible.  It doesn't show numbers at even close to the resolution of 6 degrees.  But yes you are right, Ascending you want to launch at 84 degrees and descending you want to launch at 96 degrees.

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Pand5461    91

@Alshain, NavBall shows the heading as a number at the bottom (next to HDG letters), so it's entirely possible to keep that heading within 1 degree accuracy.

But anyways, great tutorial, I can only explain such things with quite a bit of not-so-highschool maths.

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Alshain    4724
Posted (edited)
4 minutes ago, Pand5461 said:

@Alshain, NavBall shows the heading as a number at the bottom (next to HDG letters), so it's entirely possible to keep that heading within 1 degree accuracy.

But anyways, great tutorial, I can only explain such things with quite a bit of not-so-highschool maths.

Oh yeah, I guess it does.  I always forget about that, I never actually use it lol.

Edited by Alshain

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WanderingKid    199

On a side note, if you know if your next launch is going to be ascending or descending, you can adjust with shift-rotation to an 85/95 degree path on the pad.  This, of course, assumes you typically adjust the vehicle in the VAB to be facing down to turn 90, instead of right.  This takes a lot of fiddling around during liftoff out of the equation for me.

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Freshmeat    264

Would there be interest in me uploading a small Excel sheet where you enter your current date and get next asceding and decending launch time?

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