General question(s) about some orbit characteristics

[Pointy End]

I'm playing Career mode on normal difficulty, and I took on one of those "put a probe in this specific orbit" contracts. I did it, but I'm still having trouble visualizing a few things.

For the sake of argument, consider a rocket/probe orbiting Kerbin with a 5 deg inclination. Let's say the apoapsis is 80k and the periapsis is 75k. Now then, I can visualize my orbital plane with respect to Kerbin just fine. What I mean is, if you could place a stationary camera at, say, the ascending node, Kerbin would appear to rotate under the camera, right? Same for the apsis, too, right? So my question is, if I'm right about that, then in what frame of reference, if any, are the ascending/descending nodes and apsis fixed? Would they be fixed relative to Kerbol's equatorial plane? Does any of this make sense? I'm kind of flailing about, here, sorry about that.

 

[OHara]

37 minutes ago, Pointy End said:

What I mean is, if you could place a stationary camera at, say, the ascending node, Kerbin would appear to rotate under the camera, right?

Right.  You can do exactly this in map mode (either while flying or in the 'tracking station').  Double-click on the planet and use the time-warp to watch the planet rotate and any craft you might have in orbit.

By 'stationary' I take you to mean stationary relative to Kerbin, following it around in its orbit around the sun.  Stationary relative to Kerbin does not imply rotating with Kerbin, as you can look at Kerbin from a fixed direction, with a fixed backdrop of stars behind the planet, and that is what the KSP map-mode views do (if 'focus' is on Kerbin).  

The long axis of the orbit, the line from periapsis to the center of the planet to apoapsis, keeps a fixed orientation, so stays stationary in such a view.  So does the nodal line.  Bodies in motion tend stay in motion in the same direction.  This property of momentum lets bodies in orbit keep the shape of the orbit in a fixed orientation, regardless of rotation of the planet below.

Edited June 14, 2018 by OHara

[bewing]

51 minutes ago, Pointy End said:

So my question is, if I'm right about that, then in what frame of reference, if any, are the ascending/descending nodes and apsis fixed?

If you are willing to grant that the distant stars don't move much (in an angular sense) in a lifetime, then an orbit is fixed with respect to the distant stars, basically. Or in another sense, orbits are always in "universal coordinates". 

 

[Pointy End]

17 minutes ago, OHara said:

By 'stationary' I take you to mean stationary relative to Kerbin, following it around in its orbit. 

Actually I meant stationary as in fixed to the location of the ascending node, regardless of whatever Kerbin may or may not be doing below it. As you said, just like in map view.

So if the long axis keeps a fixed orientation as you say, then one could say, "this long axis points to star X, and will always do so as long as you don't do any burns."

[Pointy End]

2 minutes ago, bewing said:

If you are willing to grant that the distant stars don't move much (in an angular sense) in a lifetime, then an orbit is fixed with respect to the distant stars, basically. Or in another sense, orbits are always in "universal coordinates". 

 

Okay, this is what I thought. This leads in to the whole "Longitude of the Ascending Node" concept. From Wikipedia, and I'm paraphrasing, this is the angular measure from a reference direction moving counter-clockwise to the ascending node. In the case of the satellite/Kerbin system, the reference direction would be in universal coordinates, not based on some arbitrary longitudinal line on Kerbin, correct? The reason I bring this all up is because the contract I mentioned in my original post specified that orbit have a specific Longitude of the Ascending Node. I believe the number was 57.3 degrees. So how in the heck was I supposed to figure that out?

[OhioBob]

5 minutes ago, Pointy End said:

Okay, this is what I thought. This leads in to the whole "Longitude of the Ascending Node" concept. From Wikipedia, and I'm paraphrasing, this is the angular measure from a reference direction moving counter-clockwise to the ascending node. In the case of the satellite/Kerbin system, the reference direction would be in universal coordinates, not based on some arbitrary longitudinal line on Kerbin, correct? The reason I bring this all up is because the contract I mentioned in my original post specified that orbit have a specific Longitude of the Ascending Node. I believe the number was 57.3 degrees. So how in the heck was I supposed to figure that out?

There's a celestial coordinate system used to measure the orbital elements.  Zero longitude points in the direction of a point in space that is fixed relative to the stars.  In real life, zero longitude is along the line formed by the intersection of Earth's equatorial plane and the ecliptic plane, pointing in the direction of the vernal equinox.  In KSP it is not entirely clear what defines the direction of zero longitude.

One thing I've noticed, and this is totally unofficial, is that when you look at the "milkyway" that crosses the sky, there appears to be a bright middle to it.  Zero longitude seems to point in the direction opposite this brightest part of the milkyway.  At least that's what I recall.

[bewing]

3 hours ago, Pointy End said:

So how in the heck was I supposed to figure that out?

You don't have to. You just have to look at the pretty orbit that's plotted out in the Tracking Station and Map mode, and then match it. Make sure you aren't orbiting backwards. The displayed An and Dn are relative to your current orbit. Get the number down to zero, and profit.

There are multiple additional tricks  you can do when you are matching a displayed orbit.

 

[Superfluous J]

3 hours ago, Pointy End said:

So how in the heck was I supposed to figure that out?

18 minutes ago, bewing said:

You don't have to. You just have to look at the pretty orbit that's plotted out in the Tracking Station and Map mode, and then match it. Make sure you aren't orbiting backwards. The displayed An and Dn are relative to your current orbit. Get the number down to zero, and profit.

In fact, there are those of us who think all that extra information isn't just superfluous but makes the contracts harder for those who are learning, and should be removed entirely or at least hidden in some dropdown.

"Put your satellite in an orbit like the one shown in map mode" is all it should say.

 

[Pointy End]

8 hours ago, bewing said:

You don't have to. You just have to look at the pretty orbit that's plotted out in the Tracking Station and Map mode, and then match it. Make sure you aren't orbiting backwards. The displayed An and Dn are relative to your current orbit. Get the number down to zero, and profit.

There are multiple additional tricks  you can do when you are matching a displayed orbit.

 

Yup, that is exactly how I did it, although not at first. I got the apsis correct first, then noticed my orbit was really close to that shiny red orbit.

Hmmm...<light bulb!>

[Pand5461]

13 hours ago, 5thHorseman said:

In fact, there are those of us who think all that extra information isn't just superfluous but makes the contracts harder for those who are learning, and should be removed entirely or at least hidden in some dropdown.

And there are others who uses kOS or kRPC and need those numbers to code the guidance for automatic transfers to those orbits.

The same "extra numbers in the interface are scary for newbies and bad for sales" rationale has already taken away any hope for stock DeltaV info for vessels.

To not "make it harder for those who are learning", the info has to be represented in a "newbie-friendly" way, not taken away entirely.

[Superfluous J]

3 hours ago, Pand5461 said:

And there are others who uses kOS or kRPC and need those numbers to code the guidance for automatic transfers to those orbits.

The same "extra numbers in the interface are scary for newbies and bad for sales" rationale has already taken away any hope for stock DeltaV info for vessels.

To not "make it harder for those who are learning", the info has to be represented in a "newbie-friendly" way, not taken away entirely.

Stock dV is useful in general. Those numbers are NOT. Yes, they would somehow allow someone to code in an automatic orbiting program, and I didn't think about that, so hiding them in a dropdown is fine.

I would like ONE stock player to come on here and tell me that they used the numbers (even if in conjunction with the lines) to nail a single orbital contract. And not just the orbital heights.

[pincushionman]

1 hour ago, 5thHorseman said:

Stock dV is useful in general. Those numbers are NOT. Yes, they would somehow allow someone to code in an automatic orbiting program, and I didn't think about that, so hiding them in a dropdown is fine.

I would like ONE stock player to come on here and tell me that they used the numbers (even if in conjunction with the lines) to nail a single orbital contract. And not just the orbital heights.

It’s not possible to use that information outside of data-mining the game state. But if there were an option to have the celestial axes drawn on the focused body - or better yet, a grid - the data would immediately become relevant and useful.

[Superfluous J]

53 minutes ago, pincushionman said:

It’s not possible to use that information outside of data-mining the game state. But if there were an option to have the celestial axes drawn on the focused body - or better yet, a grid - the data would immediately become relevant and useful.

I don't see how it could be useful or relevant to someone who is just trying to play the game and match the orbit, which is 100% of the questions we get on this forum where people don't get what those numbers mean and get frustrated when we tell them to just ignore those numbers that the game is putting right up in front like they're really important. I'd be frustrated too, and angry at the developers for being intentionally obtuse about overly describing something that's already pretty complex and challenging for a new player.

Edited June 15, 2018 by 5thHorseman

[bewing]

3 hours ago, 5thHorseman said:

and get frustrated when we tell them to just ignore those numbers that the game is putting right up in front like they're really important.

On the other hand, that's exactly how an actual contract would be written up.

 

[OHara]

Well, then, I suppose we need a bug report: KSP fails to show the First Point of Aries on the skybox -- necessary to realistically interpret terms of orbital contracts!

Actually, I was surprised that there was no feedback on the bug-tracker for this very common point of confusion.  I put in a suggestion to de-emphasize angular coordinates in contract orbits

[Kryxal]

Granted, but without the fixed reference to work off of, the numbers just don't help you do anything.  "Match the displayed orbit" is far easier to understand and work with, unless you have additional tools.

[Pand5461]

4 hours ago, 5thHorseman said:

100% of the questions we get on this forum where people don't get what those numbers mean

That's the same as survivalship bias.

"People who asks about those numbers can play happily without knowing them" ≠ "No players would benefit from knowing them".

Obviously, people who know what orbital elements are don't ask questions here. That does not mean they don't care about having that info. E.g., I don't need to go to tracking station and see the orbit if I see >90° inclination and high eccentricity in the contract description. I can just decline that contract immediately.

[Dark Lion]

@Pointy End

IDK about everyone else, but I've learned a great deal more about orbital mechanics playing KSP than my ego allowed me to believe I could. Especially terms and definitions of which I was previously ignorant, before picking it up. I understood most on an intuitive level, so I flew mainly by eye. I didn't even know what delta velocity represented until I began. I just knew "burn time" and "flameout." Resonance, orbital seeding and eccentricity? No clue until comms systems were introduced. As well, there were some concepts which I didn't understand without direct involvement/ tampering. The importance of your inclination in relation to plane change and interplanetary transfers. Intercept velocity calculations came to me through exigent research and were never required, but extremely useful to chart aerobraking maneuvers. The tyranny of the rocket equation! I could probably name more, but you get the idea.

The point I'm (foolishly) trying to make is this: While the game is about aerospace and rocket science, players will learn some by doing and learn some more by asking. If there is too much information and you don't understand it, this should motivate the player to better understand what is happening and why. If that is not important to the player, that is their prerogative to skip. Otherwise, Squad has done all of us a great service in motivating us to learn anything at all. Most people pay through the nose to learn about this sort of thing professionally, or worked their BadS off to earn it. 
So, pick the game apart into pieces if you want and learn all your info-hungry brain desires! Even if its not necessary, you'll understand the game (and maybe even life outside the game) just a little bit better for it.

[Kesa]

To be honest, after following the in game tutorial about manoeuver node, you should know what periapsis, apoapsis, inclination and ascending/descending node mean. Even moreso if you watched a yt tutorial. If you know what longitude means, and most layman do, longitude of ascending node shoud be self explanatory (not the exact meaning, but what it corresponds to). And by the time you wonder about the missing parameter to characterize an orbit, you should be able to infer what argument of periapsis is. And at each step, in case of doubt, google these terms, these are simple rocket science, well explained in wikipedia.

I spent hours playing without bothering about that thing called "Isp", and I really think it is of no use for complete beginner. Is it a reason to hide it in game? In my opinion, certainly not. One day, I wondered if there was something in game indicating the efficiency of an engine, figured something akin to exhaust velocity, and looked for it in game. I figured I could divide thrust by consumption, but Isp being the only thing I did not understood at that time, I gave it a look and learnt what it was.

 

The same thing could be said about wheels and leg spring and dampening, about chute deployement altitude, or the many details given by the navball.

 

One of the key lesson I learnt in KSP is that, although rocket science can be broken into simple intuitive bits, it is huge, you can't expect to know everything at once. And it great since you don't have to. SO the mindset should not be trying to decipher every single bit of information thrown at you, but rather wondering : "what piece of information do I need to do X?" and only then "where is this info in game and how is it worded?". You're much more likely to understand a piece of information you've needed, looked for and thought about than a random one. So for superfluous information, "don't know don't care".

 

Players trying to do direct insertion or to calculate Dv manually will seek information like the orbital parameter given in the fine prints of contract, so these are not useless for everybody. In any case, you should always follow the shiny graphic stuff thrown at you first (eg the orbit in the map view rather than orbital parameter, the way point in the asame map view rather than using latitude and longitude...).