Help with orbital stuff?

[LordOfMinecraft99]

I really need help with orbital stuff, i mean i can get stuff of the launchpad and can land and dock but i really need help with orbital stuff. I just can't do it! The manoever thing does not make sense, and i don't get what all the slidy bits mean.  I also do not know what "Delta V" Or perapsis/ apoasis mean.I just really want to know because even MechJeb does not have help with orbital stuff. So, if someone could show me a good tutorial i could get a lot farther in the game. 

[Snark]

39 minutes ago, LordOfMinecraft99 said:

I really need help with orbital stuff, i mean i can get stuff of the launchpad and can land and dock but i really need help with orbital stuff. I just can't do it! The manoever thing does not make sense, and i don't get what all the slidy bits mean.  I also do not know what "Delta V" Or perapsis/ apoasis mean.I just really want to know because even MechJeb does not have help with orbital stuff. So, if someone could show me a good tutorial i could get a lot farther in the game. 

Welcome to the forums!

I suggest browsing around in the Tutorials sub-forum:

http://forum.kerbalspaceprogram.com/index.php?/forum/50-tutorials/

Some particularly useful threads:

Good luck, and welcome to KSP!

[Kar]

Welcome to the Forums and KSP.

Learn with : Scott Manley

Good flying.

Edited March 7, 2016 by Kar

[pincushionman]

Just a quick primer:

All "closed" orbits around a body are ellipses with the body at one focus (NOT the center!).

Periapsis: the point in the orbit that is closest to the parent body. At this point you are moving fastest.

Apoapsis: the point in the orbit when you are furthest from the parent body. At this point you are moving slowest.

Delta-V: Only two things are needed to completely define an orbit: position and velocity (speed + direction of travel) at that position. Once in orbit, you can't arbitrarily change position (the only way to do that is to follow the orbit); the best you can do is change to a different orbit that intersects your current one at your current position.

Since the position is the same in both orbits, the only difference is the velocities -different speeds, different directions, or both. The vector difference in these quantities called delta-V ("change in speed and direction") and describes the maneuver to get from one orbit to the other. In KSP the magnitude is the dV number shown, and the direction is marked on the navball.

You'll also see delta-V bandied about when describing ships - in this case, it's describing the total change in speed the ship is capable of (the "direction" part of velocity is meaningless when used in this manner).

In a nutshell:

- To get somewhere, you need to be in an orbit that gets there (this orbit has a periapsis and apoapsis that describes it).

- To get to a target orbit, you need to be in an orbit that intersects your target orbit somewhere.

- Once you reach that intersection point, you perform a maneuver to move from your current orbit to your target orbit. This is accomplished by changing your velocity (speed and/or direction), and is described by delta-V.

Keep in mind "target orbit" doesn't have to be a specific orbit; most of the time it's "anything with about these peri/aopapses is good enough."

Hopefully this helps a little; I know it didn't address the "slidey bits" you asked about (the pull handles on the maneuver editor maybe?), but maybe that gives you some insight into what you're trying to accomplish.

[Plusck]

Well, I think @pincushionman's answer is excellent, but I'd like to try to simplify some more. Not sure if it'll work though...

Taking the first thing, absolutely vital to spaceflight, about orbits: you are at a particular position in space, going at a certain velocity in a certain direction. Those three attributes determine absolutely, without any possible variation, your orbit around the parent body. If nothing else changes you will follow exactly the same path for eternity. And at each point in that orbit, you will have a certain amount of energy. When kinetic energy is highest, your potential energy will be lowest, and vice versa. The attributes of your orbit determine that total energy, and that total energy will also remain constant for eternity until you change it.

However, those attributes are only relative to the massive body your are orbiting. Viewed from anywhere else, your path is completely different. This isn't Einstein at work (though the principle of relativity is essentially the same) but Copernicus: trying to describe the orbits of the other planets from a geocentric perspective is insanely difficult, and sanity demands that you look at it from a heliocentric viewpoint. And so in KSP: your orbit is defined by the body you are orbiting: Kerbin within its Sphere of Influence, the sun Kerbol outside it, then each planet and moon within each nested S.o.I.

So the sliders on a maneuvre node represent the six different directions possible with reference to the massive body you are orbiting - and only that body. Faster forward is prograde and slower is retrograde (green). Outwards from the body is radial out and inwards is radial in (blue). Northwards (or what appears "up" on the map) is normal, southwards is anti-normal (red).

So if you got into a standard east-wards orbit, flying along with your face to the earth à la Superman, your head would be prograde, feet retrograde, belly radial-in, back radial-out, left hand normal, right hand anti-normal.

The problem with the Superman posture is it doesn't make much sense for navigating. Nor do all the standard positions that you see orbiting spacecraft in when watching any sci-fi. Nor does the International Space Station in all of the standard photos showing it in a face-down-to-earth position.

What makes more sense is the standard position that a Kerbal adopts when on an EVA. The head is "up", i.e. normal or "north", and the feet are "down" (south, antinormal). In virtually all ordinary orbits, those are the directions that vary the least. They are also the ones that are the most expensive to change in terms of fuel. Changing orbital plane is very costly.

Next in expense is radial in or out. Sure, you might like to just accelerate straight up from the surface of the planet but you're fighting gravity every second that you are doing it. Dragging the blue sliders may often be necessary, but they have a cost and that cost arises because you are trying to go against what gravity is trying to dictate (and will dictate, every single second you defy it). For a reasonable Kerbal on EVA who is facing the direction of travel, left is radial in and right is radial out. If you roll your ship until the navball is brown on the left, blue on the right and prograde is in the centre, you're in the standard Kerbal EVA position.

And finally, the simplest of the three pairs of sliders, forwards and backwards. Faster or slower: you change your velocity and you give gravity more or less time to catch you again. Whichever of these two directions you use, prograde or retrograde, you are also making the best use of your propellant. To gain the most orbital energy you want to rob your propellant of as much energy as you can, which means slowing it as much as possible, which means sending it directly retrograde (i.e. thrusting prograde); to decrease your orbital energy (i.e. lower your orbit) you want to transfer as much energy as possible to your propellant, which means sending it prograde.

 

So those are the six possible directions. Prograde is where you're already going, retrograde is behind, and the other four are up, down, left or right. However, obviously, if you start heading in one of those directions then "forwards" will start to swing in that direction. Burn for long enough to "normal" and that direction will become "prograde"...

 

Um, did I say I wanted to write something simple?

Anyway, going to the Mun means raising your orbit by about 850m/s prograde from low kerbin orbit. You could also just do this with a radial out burn, of course (meaning you wait until the Mun is directly overhead, point at it and burn) but that would cost you about 2150m/s.

As a favourite SF writer of mine wrote once about navigation:

"How do you navigate this thing?"

"Point."

"Point?"

"Get to the general volume and then point in the right direction."

(said another:) "Secret is plenty of power."

"Delicate finessing of delta-V is sign you haven't really got enough power."

 

 

OK, definitely didn't work for that "simplifying" bit...

Edited March 8, 2016 by Plusck