[1.7] Advanced orbital info tab

[Shmauck]

I am struggling a bit to fully grasp the content of the new "advanced orbital info tab" in the mode UI. 

As you can see in the following image I managed to establish a few equatorial orbits (inclination almost zero) around Minmus despite my ships and stations were originally coming in at an angle. So far so well.

Since 1.7 we have this nice advanced orbital info tab but I can't figure out what the LAN value means. I miss the origin of that angle. Longitudes on Earth are referring to the zero meridian in Greenwich, that's clear. But what does this Longitude of the AN refer to? And is it a local reference point on the surface of the celestial body? Probably not. Obviously it is also not the prograde vector of the body nor can it be a fixed star outside the Kerbol system.

I hope someone can help me understand the parameter in KSP so I don't have to guess where to do my inclination correction burns. And sorry if this is written somewhere. I have looked in the in-game help page, in the wiki and searched the forum without success.

Thank you in advance!

[Superfluous J]

22 minutes ago, Shmauck said:

Since 1.7 we have this nice advanced orbital info tab but I can't figure out what the LAN value means. I miss the origin of that angle. Longitudes on Earth are referring to the zero meridian in Greenwich, that's clear. But what does this Longitude of the AN refer to? And is it a local reference point on the surface of the celestial body? Probably not. Obviously it is also not the prograde vector of the body nor can it be a fixed star outside the Kerbol system.

I hope someone can help me understand the parameter in KSP so I don't have to guess where to do my inclination correction burns. And sorry if this is written somewhere. I have looked in the in-game help page, in the wiki and searched the forum without success.

Thank you in advance!

Honestly I ignore those numbers. Always have.

LAN is the Longitude of the Ascending Node, so it should be "where your ascending node is around the orbit" in relation to SOMETHING. That something in orbital mechanics is generally a defined spot (well, a line from north to south through a spot) in the sky.

But no clue if that's true here. Like I said those numbers have never, ever helped me in any way so I ignore them.

Maybe it's the engineer in me beating the mathematician, but if I can't tell whether or not the orbit is perfect, then it's perfect.

[Shadowmage]

https://en.wikipedia.org/wiki/Longitude_of_the_ascending_node

The origin is defined (for Earth) to be " the First Point of Aries as the origin of longitude "

On Kerbin... IDK; probably defined as a line from the sun to Kerbin on a specific in-game date.  IIRC the KSP wiki may have more precise information.

 

Really though -- LAN is not a number that a player need normally concern themselves with.  Only really needed if you are trying to replicate a set of orbits from orbital parameters.

 

[Shmauck]

I found that "first point of Aries" as well. This is for sure not the case in KSP 

To put it simple: How do I know where to burn an inclination change to turn an inclined orbit into an equatorial one?

I assume that if I knew the LAN then I would know where to burn anti-normal so I can flatten that out. 

How do you guys do it? 

[bewing]

To create an equatorial orbit, you burn when you are crossing the equator. The easiest way to know that is to open a KerbNet window. The game has an arbitrary point in the sky that serves as the universal referent for LAN, but LAN is only a useful number when you are using mods -- not in the base game.

 

[OHara]

When this came up before, OhioBob remembered (correctly, as we later confirmed) that zero-celestial-longitude points directly away from the center of the galaxy in the skybox

Now we have a nicer-looking skybox, without such an obvious center to the home galaxy, but I attached screen shots of the bit of sky that serves the role of 'first point of Aries', and of the easier-to-find galaxy in the opposite direction. 
he Alt-12 debug menu Flight Info also gives current latitude of the craft, for those of us who don't use Kerbnet.

Maybe we should suggest that Squad not display the LAN in the orbital-information tab, because it is never useful for normal gameplay.

[mikey117]

For Minmus i personally try to get a low orbit rescue mission early game. I will then rescue the kerbal and leave the pod in orbit ,as the low orbit ones tend to be on an equatorial orbit.

You can then target this vessel for a reference point to set up inclination change.

 

[Shmauck]

Thank you all for your replies. These are definitely helping me understand KSP better. Also I never used KerbNet yet and will surely change that.

Too bad I terminated all the abandoned pods of rescued Kerbals. Didn't know it would bite me later.

Many thanks!

[Dafni]

6 hours ago, OHara said:

 

Maybe we should suggest that Squad not display the LAN in the orbital-information tab, because it is never useful for normal gameplay.

Yes, I believe this would be a good idea.

[mystifeid]

I don't know about that. When playing with Mechjeb I often use the LAN to change from one polar orbit to another required polar orbit . Speaking of Mechjeb, you could always use the LAN module in the Maneuver Planner to change your LAN to 0° - maybe best to be in a polar orbit - and see where the line between DN and AN is pointing. (Or I suppose, with the feedback from the Advanced Orbital Info, you can just as easily do this without MJ)

Edited May 24, 2019 by mystifeid

[EasyAce]

So how do we utilized the "Ejection" field? It seems to be degrees to something... "angle between the craft, the orbited body and the parent"... well ok... but how do I use that??

[OHara]

47 minutes ago, EasyAce said:

So how do we use the "Ejection" field?

There is a useful idea with a strange name, the 'ejection angle', that means where on your orbit you should fire the engines to reach another planet.  The inter-planetary planning tools like  Launch Window Planner and Transfer Window Planner tell you this angle so you know when to burn.  

(For example, when orbiting Kerbin and planning to go to an outer planet, you have to make your ejection burn about 140° or so ahead of the prograde direction of Kerbin's motion, so that you end up going in Kerbin's prograde direction by the time you escape the sphere of influence.)

But I have not found any way to use the 'Ejection' field in KSP.   This field shows the current angle of the craft, but I want to set the angle of a maneuver node to plan the burn.

[EasyAce]

13 hours ago, OHara said:

There is a useful idea with a strange name, the 'ejection angle', that means where on your orbit you should fire the engines to reach another planet.  The inter-planetary planning tools like  Launch Window Planner and Transfer Window Planner tell you this angle so you know when to burn.  

(For example, when orbiting Kerbin and planning to go to an outer planet, you have to make your ejection burn about 140° or so ahead of the prograde direction of Kerbin's motion, so that you end up going in Kerbin's prograde direction by the time you escape the sphere of influence.)

But I have not found any way to use the 'Ejection' field in KSP.   This field shows the current angle of the craft, but I want to set the angle of a maneuver node to plan the burn.

Agree with you - I often plan my ejection phase to that when the vessel leaves the Kerbin SOI it goes paralell with the trajectory of Kerbin it self... but I haven't found a clear link between this and the "Ejection" angle field in the advanced orbit tab info