How to Read the Navball.

[Vanamonde]

Although the main view gives you pretty pictures to look at, space flight is too complex to conduct by eyeball. That's why the game gives you two critical tools, which are map view and the navball. Most of your actual flying will be done using these tools. The navball is not something most of us are used to using, since we normally travel in the two dimensions of the earth's surface, so here is an explanation of the navball, what it does, and how to read it.

While your ship moves around in space it will be facing in different directions, and that can get confusing. So the globe of the navball maintains its orientation while you move and symbols on it tell you various useful things. Think of the globe as a map in 3 dimensions.

The navball is derived from instruments invented for airplanes, and so is easiest to explain in those terms. The blue side represents the sky, and so it is "up," which in space is away from the center of whatever world that governs your current Sphere of Influence, or SOI. The brown side is dirt, and so represents "down," which is toward the center of the current world. (Keep in mind that these up/down directions are relative to the world, and will change as you move around the world.)

The game's navball has three modes, which are surface, target, and orbit. It will switch from one to another automatically at times, but you can also cycle through them by clicking in the speed rectangle at the top of the instrument. In surface mode, your speed is measured relative to the ground. In target mode, your speed is measured relative to a target vessel you have designated, and a couple of new markers appear. In orbit mode, your speed is measured relative to the whole game universe, and some additional markers replace a couple of the target mode markers.

The numbers on the navball are degree angles (up and down) and compass headings (left and right).

The gold line runs from the zenith to the nadir on the zero degree meridian (don't worry if you don't know that that means; most of the time, you don't need it). East (relative to the current world) is the 90 compass heading on the horizon (where the brown side meets the blue side. 

East (the 90 line) is especially important, because all KSP worlds rotate in this direction, which means you get a small speed boost when taking off in that direction, and you need to brake a little less when landing in that direction. So most of your takeoffs and landings will be done while heading east. In all of the illustrations in this guide, the ship is orbiting west to east, which is counterclockwise from the camera's perspective. 

The numerical readout at the top of navball is your current speed, and the spot you click to change navball modes. The number at the bottom is your current compass heading. Along the left side of the main screen navball is an indicator that shows your current throttle setting. This runs from zero thrust to full, and while it has gradations marked on it, they don't seem to actually mean anything. (They are 1/15th of full capacity per notch, for whatever that's worth.) The short version is that it's proportional, so for example, half the gauge is half thrust. (Incidentally, there is no gauge like this in IVA view, although there is a sliding throttle handle that actually does move in proportion to your throttle setting.)

Along the right side of the navball version on the main view (but not the IVA version on the ships' internal instrument panels) is a meter that measures the acceleration that is currently acting on the ship. These accelerations are measured in earth-gravity-equivalents called "G"s, and so this indicator is commonly called the G meter. The meter is marked from -5 to +15. The meter indicates the sum of all accelerations acting on the ship at the moment, including engine thrust, rotation, and gravity. So when you are sitting on the launchpad with the engines off before launch, it will read 1 just from Kerbin's gravity, and when you are freefalling in space, it will read zero. Very rarely, the gauge may dip into the negative, as when your capsule bobs up again after splashing down. Anyway, the G meter is most useful as an indication of how hard your engines are increasing the speed of your ship, and how much speed you are shedding through aerobraking. There are safely low (green) and dangerously high (red) zones indicated on the G meter, and kerbals may pass out or even die if the Gs get too high for too long (if you have that option turned on). Ships are also subject to acceleration damage, and structural failures (parts breaking off or exploding) can occur at 1.5Gs or more, depending on the size and design of the ship, especially during launch.

These are the 3 most important navball symbols, in a pic I stole from somebody on the internet:

The attitude marker (the little -v- symbol) is kind of like looking at your airplane from behind, with its wings sticking out to the sides. It is always at the center of the ball, and the rest of the device moves around it. It tells you which way your ship is currently pointed. In the example below, the ship has its nose up (the pointer is over the blue side of the navball) and its left wing is low (because that side of the marker is angled "down" toward the ground).

 

The other two most important symbols are prograde and retrograde. In "orbit" and "surface" navball modes, the prograde marker tells you which direction you are currently travelling, and the retrograde marker is the opposite of that marker, 180 degrees away from prograde. In the picture below, the rocket is moving upwards (prograde marker is over the blue side) even though the nose of the ship is pointed down (attitude marker is over the brown side).

Thrusting toward the prograde marker will speed you up, and thrusting retrogade will slow you down. (This has other effects, too, but that's a subject for another time.) But in "target" navball mode, flying toward the prograde marker will bring you closer to the target ship, and retrograde away from it. (You can only switch the navball to target mode if you have something already targeted.)

If you have something targeted, two more symbols appear on the navball. These pink markers also have "toward" and "away from" versions, but these point toward or away from the target ship, and only if you do have something targeted.

Note that these pink target markers tell you which direction the target is RIGHT NOW, but in target mode, the prograde and retrograde markers change function, and indicate the relative velocity of the target ship. Burning target-retrograde reduces your speed relative to the target, which is extremely useful during rendezvous, because it has the effect of matching paths with the target and bringing your ship to a relative stop. Burning target-prograde is seldom advisable, as you are generally approaching at high speeds already, but there are times when it is useful. 

The blue marker only appears if you have a maneuver plotted somewhere along your path. If you have more than one maneuver plotted, the display applies to the first upcoming maneuver. The blue maneuver marker tells you in which direction to point the attitude symbol (the nose of your ship) for that maneuver. When the maneuver marker is off the edge of the navball's exposed surface, a blue arrow points to its location. 

 

If you do have a maneuver node plotted, a curved yellow bar graph appears next to the navball. This visually indicates how long your burn should be to make that maneuver, and it runs down as you burn. To the upper right of it, a numerical counter indicates how much delta-V (speed changing) remains to complete the manuever. To the lower right of the bar graph, timers count down to the moment you reach the next maneuver node (the "node in..." clock) and an estimate of how much longer the burn should last ("Est. burn:"). Note that many factors are involved in these calculations, and the numbers and bar graph are guiding approximations, and may change before and during the maneuver burn. 

You will see 4 other markers on the navball. These can be harder to explain. They are direction indicators useful for certain kinds of orbital maneuvers, but these directions are relative to the motion of the vessel. 

  

Radial is 90 degrees "up" from the vessel's current prograde, away from whatever body the ship is orbiting. Antiradial is, as the name implies, the opposite direction, 180 degrees away from radial, and "down" toward the body the vessel is orbiting.

Burning in these directions  raises or lowers the next half of the orbit, but lowers or raises the other half in the opposite manner. Usually, this is used to bring one ship's orbit closer to another ship's orbit for rendezvous. 

Base state

 
After burning radially 

After burning antiradially. 

 

Taking prograde as forward and radial as up, normal is then 90 degrees to the left of prograde and antinormal 90 degrees to the right of prograde. If a ship burns in these directions, the height of the orbit will stay the same, but the inclination will change (assuming the ship rotates to stay facing normal/antinormal throughout the burn). That means that the angle of the orbit will change: say, from this one 

to this one. 

 

This doesn't explain everything you need to know to get where you want to be, but I hope it has made the navball understandable.

Edited March 31, 2017 by Vanamonde
Updating.

[astropapi1]

Thanks for doing this! I wish I'd had this when I first played the game back in 0.13.3

It will help newbies a lot.

[Finnerty]

Yes, very helpful, good job.

[beg]

Thank you! It seems to be not so difficult.

[Voidryder]

Very nicely done.

[Pawelk198604]

I heard that navbal can display g-meter it is true?

[automcdonough]

I heard that navbal can display g-meter it is true?

right-hand side of the ball (right under SAS indicator) is the G-force meter.

Keeping it out of the red usually a good idea.

Left side is throttle of course.

[Pawelk198604]

right-hand side of the ball (right under SAS indicator) is the G-force meter.

Keeping it out of the red usually a good idea.

Left side is throttle of course.

Thanks, i think Squad should make it in digital display

[Vanamonde]

Thank you for pointing out that I neglected to address the throttle and G meter, gentlemen. I have fixed that now, and updated the guide to include the new anti-maneuver marker.

[100ideas]

Thanks for the informative thread!

After reading here and getting more details from the Kerbal Navball Wiki entry, I made a quick sketch of where I think the vectors are in a simple orbit. Does this look right? Let me know - I'm thinking about making a vector image for the wiki page. Thanks!

[Vanamonde]

Your diagram looks right to me.

And I really need to get around to updating this with the additional navball symbols they've introduced.

[JackBush]

On 5/20/2013, 6:12:53, Vanamonde said:

snipped for brevity

As everyone says, this is excellent. The problem is that it's now dated and the images are gone. Can you fix this? 

[Vanamonde]

I've been meaning to get around to it. Thanks for expressing interest. It helps me get motivated. 

[Vanamonde]

In response to popular (well, JackBush's) demand, I have updated this guide. 

[Mikki]

On 19.12.2015 at 4:14 AM, Vanamonde said:

In response to popular (well, JackBush's) demand, I have updated this guide. 

This one should be stickied for all times, it is basic knowledge of airplane, spacecraft and other vehicles navigation tools. We might forget too fast when very young Kerbalers start developing their space program, anything must be explained somewhere, and the Navball is absolute essential! 

[F9800]