launching into the inclination you want

[MPDerksen]

(lots of posts today, sorry.)

except for a rare launch where I want a Polar orbit, I 99% of the time just do the standard gravity turn to the East.  The NavBall isn't especially clear to me when trying to set up a launch at an inclined orbit with any specificity.  

Goal #1:  Rescue a Kerbal that is in an inclined orbit better than just going equatorial and then having to burn Normal/Anti-normal to intercept.  Waste of fuel!

Goal #2:  Same as goal #1, but in reference to Minmus.

Tips?

Michael  

[Zhetaan]

13 minutes ago, MPDerksen said:

The NavBall isn't especially clear to me when trying to set up a launch at an inclined orbit with any specificity.

The navball lacks resolution.  It's like using a ruler when you need a micrometer.  This is especially true for launches, because launches, unless you're having a particularly bad day, go up.  However, the various headings on the navball that you want are easiest to find on the side, not the top.  It can be done but an error of one degree on the side can be forty or more at the top.

That's why the navball also includes a compass heading readout at the bottom.  However, that readout is not very useful in orbit:  for example, you can launch due north to get into a polar orbit, but you end up heading south for half of that orbit, so you need to know when to ignore the readouts.  An okay approximation is to launch to the correct heading and then roll the rocket so that heading is in the position normally occupied by 'east' on the navball, and then fly it as though it were a standard ascent while ignoring the heading readout after that.

18 minutes ago, MPDerksen said:

Goal #1:  Rescue a Kerbal that is in an inclined orbit better than just going equatorial and then having to burn Normal/Anti-normal to intercept.  Waste of fuel!

Goal #2:  Same as goal #1, but in reference to Minmus.

Tips?

You need to know about something called the ascending node.  The ascending node is the point where an inclined orbit breaks the equatorial plane (specifically, where it breaks the plane going celestial north, or up from the perspective of someone standing at the north pole--there's a descending node for the other side of that orbit), and that's important to you because, since you start on (or very near) the equator at the KSC, launching at the ascending node of whatever you want to intercept allows you to launch directly into the correct inclination and end up in a coplanar orbit with your target.

Finding the ascending node can be tricky without mods, but there are numerous tutorials on the subject--especially for Minmus, since launching directly into Minmus's plane is a common learning step for this sort of thing.  I'd link them, but I am just about out of time for now.

[18Watt]

I’ll try to post some screenshots later, but here’s the method I use.  For me, the inclination I’m aiming for is Minmus, so I’ll use that in my example, but should work with any orbit.

I select Minmus as a target.  This isn’t required, but makes my target orbit a different color.  In the next step I’ll be looking at my target orbit (Minmus) and the Mun’s orbit.  Having your target orbit a different color than the Mun’s makes it easier to see.

Next I orient the map view so I am looking straight down at Kerbin’s equator.  I’m zoomed out far enough that Mun’s orbit fits entirely in the view.  Ideally, you should be looking edge-on at Mun’s orbit- in other words Mun’s orbit should just appear as a straight line, not an ellipse.  I use Mun as a reference because it’s basically a perfect 90 degree reference.

Ok, next step is warping to your launch window.  Your launch window is when your target orbit (Minmus in my case) intercepts Mun’s orbit.  When the launchpad is directly under where these two lines cross, launch!

Next step is your gravity turn.  You will need to determine if you need to aim for slightly less than 90 or slightly more than 90.  In the case of Minmus, I aim for either 82 or 98 degrees.  Heck, let’s round those to 80 and 90 degrees.

During the initial climb, I’m just trying to establish a slight deviation above or below 90.  Most of my launches are pretty busy below 30kM, so I can’t check my progress in map view.  Once above 30kM I can usually switch to map view, and fine tune my trajectory.  I’m looking at either the AN or DN value.  If they’re not zero (they never are..), I bump the nose a bit north or south, to get the AN/DN values as close to zero as I can.

90% of the time I end up with less than 1.0 degree inclination difference to my target (Minmus).  Anything less than 1.0 deg. is ‘close enough’, I can easily get a Minmus encounter at that point.  In your case, you are trying to rendezvous with a vessel, and will eventually need to match inclinations exactly.  My method will get you close, but you’ll still need to fine-tune your inclination once in orbit.  I would suggest your goal should not be 100% accuracy, but to reduce your inclination burns as much as possible.  

Example- your target orbit is offset 20 deg. from equatorial.  If you launch to an equatorial orbit (90 deg) you would need to burn Normal or Anti-Normal 20 deg. to fix that.  If you can get within 5 degrees, that’s potentially a lot of fuel you just saved!  I mention this because it did take me a bit of practice to start getting close to my intended inclination.  I don’t use mods, so I’m relying on my ‘Mk I Eyeball’ for precision.  However, I’m sure there are mods which can also aid you with this.  For me, it’s more fun and challenging to just eyeball it, and pretty rewarding when I end up close!

Good Luck!

[Epicdreamer]

A visual tip for #2. In map mode select Minmus as a target. The orbit of Mun is perfectly equatorial and circular. Zoom out and align untill you see the Munar orbit perfectly edge on in front and Minmus orbit behind Kerbin. Now by turning the camera around Kerbin search for where both orbits cross with Kerbin in the centre. Re-align Munar orbit edge on and zoom in until you can see the launchpad position on the globe. Wait (or timewarp) until the launchpad, the centre of Kerbin and Minmus orbit are in line. Adjustment of cameraposition may be needed to keep the descending (or ascending) node behind the centre of Kerbin. Launch westwards and steer a bit towards the target marker when it gets visible on the navball to (roughly) align your orbital plane and go into orbit. Normally then I only need a little planechange correction burn to align my orbit with Minmus's... and burn for a hohmann transfer.

Edited July 3, 2019 by Epicdreamer

[MPDerksen]

I found this trick just now in a search (when I should be working)  

However you lost me at 2 points at the end. I thought the standard gravity tun goes right/east?  Second, the target market points directly at the target, not its orbit, right?

[bewing]

33 minutes ago, MPDerksen said:

the standard gravity tun goes right/east? 

Yup. I'd try to tease you about west being east if you just look up from the bottom, but I'd probably just confuse you.

33 minutes ago, MPDerksen said:

Second, the target market points directly at the target, not its orbit, right?

Yup, which is why you usually use that trick when your target is right over your head, so that the target and the orbit are basically in the same place.

[18Watt]

Hokay!  Here goes, some screenshots.  Let's go to Minmus!  The goal here is to launch into an orbit with an inclination close to that of Minmus.  Or, whatever vessel you are trying to rendezvous with.  If you are using my 'eyeball' method, I'd say anything within 10% is really good.  For this example, I got lucky, and launched into an orbit about 0.1 degrees off of Minmus's inclination.  I don't always get that, and I'm always really happy with any inclination within 1.0 deg.

Step 1.  Select Minmus as a target.  This is mainly to give you some contrast in orbit colors, so you don't get confused.

Step 2.  Rotate Map view until you are looking edge-on at MUN's orbit.  Mun's orbit should look like just a straight line, or as close as you can get it..

Step 3.  Don't change your view orientation!  You want to launch when the launchpad is directly under the intersection of Minmus's (or your target) orbit and Mun's orbit.  It should look like the following screenshot.  NOTE in this instance, I'll need to launch slightly northerly (080).  If I waited about 1/2 day, I'd be on the other side of Kerbin, and would have to launch slightly southerly (100).  Here's where KSC should be for your launch window.  (I'm launching from KSC).

Step 4.  Gravity Turn!  Roll over to 90 deg. just like always, but then aim for a little 'north' or 'south'.  In this case I'm aiming for about 080 deg.  It's hard to 'eyeball' this, and very easy to over-shoot.  A little practice will make this smoother.  Again, it's just like a normal gravity turn, but you're just aiming for a little north or south of 90.

Step 5.  Fine-tune your burn.  When able, switch to map-view.  I don't do this early in the launch, because there's boosters to shed early on.  But as soon as I can, I switch to Map View, and look at the AN/DN values.  If they are not zero (they never are..), I nudge the nose a little north or south.  In this screenshot, the DN is closest to me (0.3 deg.), so I nudge the nose NORTH (towards 0) a little.  In this case, with minimal effort, I was able to get the AN/DN to be 0.1 deg.  That's pretty close!  Again, for Minmus, anything less than 1.0 deg is 'Good Enough!'

Step 6.  Once you have the AN/DN as close to zero as you can get (Anything less than 1.0 deg. is just showing off!), burn Prograde, and circularize your orbit like normal.  I like to shoot for about 100kM, but use whatever orbit you like.  

Step 7.  Don't forget to deploy your solar panels and antennae!  

Step 8.  Burn to intercept your target.  If your target is a vessel, you'll want to match inclinations exactly.  In this case, my target is Minmus, an inclination of 1.0 deg. or less is fine.  For Minmus, I start my burn when I'm about 110 degrees behind Minmus, but you could use maneuver nodes to double-check. In the following image, Minmus is at 12 o-clock.  I would start my prograde burn when I'm at about 4 o-clock.

Hope this makes sense!  For other orbits, the principle is the same.  However, the further from 90 your target is, the more difficult it is to get within 1.0 degrees.  A good goal to shoot for is an inclination of 25% or less of the original inclination.  So, if your target is 20 deg. off of 90 (say 70 or 110), then if you can launch into an inclination of 5.0 deg. or less, you are doing great.  For polar orbits (say 70-90 deg), if I can get within 10 or 15 degrees I am really happy with that.

You could probably get closer using mods (like MechJeb), but what fun is that?  Nice to be able to just 'eyeball' it, and get pretty darn close.  Again, good luck!

[Empiro]

Imagine your target's orbit (whether Minmus or a stranded Kerbal) as a flat disc. If you finish your burn when not in the same plane as that disc, then no matter what, you won't have the same inclination as your target (because your orbit's plane contains the point where you finished your burn). The easiest way to finish your burn in the same plane as your target is to launch when you're in the same plane as your target, but that can be hard without mods.

Without mods, one trick is to follow the method above. You take advantage of the fact that the Mun's orbit is 0-inclination and perfectly circular, so it's a pretty good proxy for how you travel as you sit on the launchpad.

Another trick to get into the same plane is to launch a simple satellite into say, a 100km circular orbit with 0 inclination (use the Mun as a target to eliminate any inclination). Switch to the satellite and set Minmus or the Kerbal as the target. It'll show you where the ascending / descending nodes are, and because the orbit is a lot closer to Kerbin, you can more easily tell when the KSC is right under it.

When launching, you'll want to get into the same inclination as your target. Again, mods can make this easier, but if you don't want to use one, you can use the pink target markers to help out. As you're launching, imagine a line going from your prograde maker to the pink target or target retrograde marker (doesn't matter which one). You want this line to pass through the horizon at a 90 degree angle. Essentially, you don't care about the radial (up/down) component (because the target can be anywhere along its orbit), but you want to minimize the radial (left/right) component. The map mode will also show your inclination, and you can use it to make small left/right corrections as you're burning.

[MPDerksen]

On 7/3/2019 at 3:52 PM, 18Watt said:

Hokay!  Here goes, some screenshots.  Let's go to Minmus!  The goal here is to launch into an orbit with an inclination close to that of Minmus.  Or, whatever vessel you are trying to rendezvous with.  If you are using my 'eyeball' method, I'd say anything within 10% is really good.  For this example, I got lucky, and launched into an orbit about 0.1 degrees off of Minmus's inclination.  I don't always get that, and I'm always really happy with any inclination within 1.0 deg.

 

You could probably get closer using mods (like MechJeb), but what fun is that?  Nice to be able to just 'eyeball' it, and get pretty darn close.  Again, good luck!

Tried it.  Ended up in orbit with an An of 0.5.  Not bad, right?  I launched at 84 degrees and was pretty spot on.  HOWEVER, there are published inclinations for minmus.  How about for targets of unknown inclinations?  What I'm currently doing is launching and leaning straight at 90, then, when I hit about 10km up, I check the An for my target, and adjust.  Crude, but effective.  And no, I'm currently not using any mods.

[Superfluous J]

1 hour ago, MPDerksen said:

Tried it.  Ended up in orbit with an An of 0.5.  Not bad, right?  I launched at 84 degrees and was pretty spot on.  HOWEVER, there are published inclinations for minmus.  How about for targets of unknown inclinations?  What I'm currently doing is launching and leaning straight at 90, then, when I hit about 10km up, I check the An for my target, and adjust.  Crude, but effective.  And no, I'm currently not using any mods.

That's basically what I do. I target Minmus before launch, then launch at an eyeballed an/dn, tilted north or south as needed, and then at about 10-20km up (as I'm mostly tilted over, going maybe 1000m/s) I look at the actual an/dn of Minmus and usually I'm within 1 or so degrees. I then tilt a bit north or south to correct that as good as I can. Usually after that I'm within 0.5.

[18Watt]

2 hours ago, MPDerksen said:

Tried it.  Ended up in orbit with an An of 0.5.  Not bad, right?  I launched at 84 degrees and was pretty spot on.  HOWEVER, there are published inclinations for minmus.  How about for targets of unknown inclinations? 

Here’s one suggestion- If you happen to have a vessel in a equatorial orbit, switch to that vessel, and compare it’s inclination to your target’s.  Otherwise just eyeball it.

And yes, an inclination of 0.5 degrees is awesome!  I’d say you have it nailed.  The idea is to get on track as soon as you can, instead of spending DV going the wrong way.  At 10kM you don’t have much velocity yet, so it’s still really cheap to make course corrections.  

Way to go!

[TheFlyingKerman]

Another trick: rotate your rocket in the vab before launch.

[ClamBoy]

One of the first things I do in a new save is launch a little satellite that matches Minimus inclination so I can match that instead of faffing about with the view to see Minimus orbit. I launch it equitorially with enough dv to make the inclination change to match Minimus. While in map view, you should be able to see the satellite's orbit as well as your launch vector.
If you run Kerbal Alarm Clock, target the satellite and set an alarm for the ascending or descending node. 
While this doesn't help directly with goal #1, it makes #2 much easier to handle.

Edited July 8, 2019 by ClamBoy

[Superfluous J]

1 hour ago, ClamBoy said:

One of the first things I do in a new save is launch a little satellite that matches Minimus inclination so I can match that instead of faffing about with the view to see Minimus orbit. I launch it equitorially with enough dv to make the inclination change to match Minimus. While in map view, you should be able to see the satellite's orbit as well as your launch vector.
If you run Kerbal Alarm Clock, target the satellite and set an alarm for the ascending or descending node. 
While this doesn't help directly with goal #1, it makes #2 much easier to handle.

I like this idea. Instead of KAC, the do-everything-you-can-by-eye player in me thinks instead you should have 2 such craft, one matching orbits with Mun (i.e. equatorial) and one Minmus. Then you can very easily just see where they cross and launch when your space center is under that point.

[ClamBoy]

On 7/8/2019 at 4:21 PM, 5thHorseman said:

I like this idea. Instead of KAC, the do-everything-you-can-by-eye player in me thinks instead you should have 2 such craft, one matching orbits with Mun (i.e. equatorial) and one Minmus. Then you can very easily just see where they cross and launch when your space center is under that point.

Now that is clever. I never had much success eyeballing the AN/DN. Having that second orbit makes for an easy visual reference. Very cool.

[Tyko]

I turn the rocket on the launch pad to launch in the desired direction. If I need a 30 degree incline I just turn the rocket to sit at a 30 degree angle on the pad.

This way, when I launch I just have to pitch down like I normally would and don't have to mess with trying to do any complex steering on the way up. It works great and it's super easy.

[Mahnarch]

On 7/17/2019 at 1:13 PM, Tyko said:

If I need a 30 degree incline I just turn the rocket to sit at a 30 degree angle on the pad.

How does one get a perfect(ish) angle without a navball in the VAB, exactly.

Asking just so, you know, some newer player can know - since all us vets already know...

 

*eyeballs the room while sipping coffee*

[Tyko]

35 minutes ago, Mahnarch said:

On 7/17/2019 at 10:13 AM, Tyko said:

If I need a 30 degree incline I just turn the rocket to sit at a 30 degree angle on the pad.

How does one get a perfect(ish) angle without a navball in the VAB, exactly.

Asking just so, you know, some newer player can know - since all us vets already know...

 

*eyeballs the room while sipping coffee*

Shift & Left Click to grab your entire rocket. Then hold down the Shift key and use the Q or E keys to rotate the rocket on it's long axis. Since you're holding down Shift each step of rotation will be 5 degrees.

 

Edited July 20, 2019 by Tyko