Orbital alignment for dummies?

[Skorpychan]

So. I have a few station components up in orbit, and I want to slot them together. They're in fairly similar orbits, but not completely the same.

Trying to align them seems to only waste fuel for nothing. The wiki articles on changing the orbits don't make sense to me. And maneuver nodes are confusing.

Halp?

Edited June 28, 2013 by Skorpychan

[Shpaget]

Take one of the ships and select the other one as target. In map view you'll get two new points on the orbit line called "Ascending node" and "Descending node". They tell you the difference in the inclination of the two orbits in question. Your first maneuver is to get rid of that difference. Click on the orbit on one of those nodes and pull maneuver node in the "up" or "down" direction depending on the node you picked. Make sure your inclination difference is as small as possible (0.1° - 0.2° is easily achievable and is fine enough).

After that you need to match the phase. If the ship you are controlling is behind the target ship, enter a lower orbit to catch up. If it is in in front of the target, a higher orbit will slow you down. You only need to adjust one side of the orbit (periapsis or apoapsis). Start with small adjustments (10-20 km difference on one side, as little as possible height difference on the other). You'll see how it is going, adjust accordingly.

If your crafts are in equatorial orbits it helps to point one ship's docking port directly towards north so it doesn't spin around.

Once you fiddle with the orbits to the point where their closest approach is 2-3 km or less (you can get that information from the map view), you can switch to stage view or docking and use RCS for the final approach. Don't go too fast, or you could alter your orbit too much on the other side.

Once you start using your RCS, the first thing to do is to kill all the lateral motion (with navball set to target and not orbit or surface, you should match your prograde marker with the target marker). Make your final approach slow (no more than 5-10 m/s when closer than 200 m and 1-2 m/s when closer than 50 m. Under 20 m you shold go as slowly as possible.

Use your main engine with care. It can drastically change your orbit and throw away all your hard work.

[Skorpychan]

Okay, and how do I adjust the maneuver node UI so it shows the indicators for doing that, rather than just eyeballing it?

[Sirrobert]

Okay, and how do I adjust the maneuver node UI so it shows the indicators for doing that, rather than just eyeballing it?

Adjust what? Open a node, and you have 6 axis you can drag. Drag the purple one for inclination. Eyeball it to rhoughly the same, and keep during the burn keep your mouse over the accending/deccending node. You can see in real time the exact number. Burn at a low thrust, until the number reaches as close to 0 as you can (ít's quite easy to overshoot).

Alternativly, use mechjeb

[Tw1]

Alternativly, use mechjeb

I must protest! Save mechjeb until you've mastered things for youself, IMHO.

Edit: Oh, you only meant the inclination adjustment. Ok.

Having them in similar orbits actually makes things much harder, unless you want to warp for hours untill they get close. The trick is to put them into orbits with a fair amount of difference between them.

Objects in lower orbits take less time to go around the planet than ones in higher orbits.

Using this, you can get the object in a lower orbit to catch up with the one in a higher orbit.

Aligning orbits is important.

An essential part of rendezvous is putting the other vessel as your target. To this by clicking on its orbit, and selecting "set as target".

This gives you a couple of extra tools.

The AN and DN are where your orbit is lined up with the other vessel's orbit. Here is where you want to perform inclination adjustments.

Set up a maneuver node at one of these points.

Turn the view so that the target orbit appears as a flat line, then use the purple handles on the node to change your one until it appears lined up with your target's orbit. Then perform that burn.

To meet up with the target, make a maneuver node, and plan an orbit that meets the orbit of your target. You should see markers that show where your ship and the target will be at the closest approach. If you don't move the node around a bit.

Keep moving the node until you get close. This will take practice.

Within 2.5 Km, or thereabouts, is what you want to aim for.

If you get that, perform that burn. Otherwise, you may need to make a few more orbits before everything is lined up. Then try again.

Once you get close, you need to kill your relative velocity. This can be done by clicking on the navball's speed display until it's in target mode. Then, the prograde and retrograde markers will show your movement compared to the target vessel. You'll need to burn pointing towards one of these to reduce the speed shown to zero. Then, you're almost there.

Next you need to aim yourself towards the target. This is one of the pink markers. Burn to approach it, but stay slow. You'll need to burn facing away from the target when you're close, to slow down (to zero) again, if you want to dock, and not crash.

Docking is a separate challenge, and I'm not that good at it. So I'll have to leave you in someone else's hands for that.

Best of luck with the station! Stations are awesome.

Edited June 27, 2013 by Tw1

[Sirrobert]

I must protest! Save mechjeb until you've mastered things for youself, IMHO.

Edit: Oh, you only meant the inclination adjustment. Ok.

Au contraire monsieur.

I learned how to dock and rendevous with Mechjeb. First full autopilot (cause there was no way in hell I was going to get 2 pieces close by myself, let alone dock).

After a few times I started toggeling docking autopilot on and off to save RCS (no use making microadjustments when you are heading towards the port.

Again later (and watching Scott Manley) I figured out how to use smart ASS, build myself an RCS tug and started practicing with moving the tug around to different dockingports on my station.

Now, I can even dock RCS inballanced crafts thanks to smart ASS, dockingcam and my own smarts.

Same thing with rendevous. Used to do full autopilot, now the planner to make perfect manouvernotes (I'm lazy), and than do the rest myself.

Though I let the manouver-autopilot handle the inclenation adjustment. It's alot better at making those tiny 4m/s deltaV adjustments needed.

O and i use the rendevous autopilot to guide my crafts the finall 2 km to my main space station. The reason for this is simple, I don't trust my laptop to respond fast enough to my own commands with 500 parts on screen.

Mechjeb is a wealth of tools, for every kerbalnaut of every level of skill

[Mr Shifty]

You actually don't need a maneuvering node at all. You have to set one vessel as your target, and make sure your NavBall is set to target mode.

1) Adjust inclination as others have described. It's actually possible to do a rendezvous without adjusting inclination, but your indications are harder to read.

2) Go to map view and determine whether your target is ahead of you or behind you. If it's ahead, do a slow retrograde burn until your closest point of approach to the target is within about 20 km. If your target is behind you, do a prograde burn to the same effect. Then warp until your vessel is about 20 km from the target. Now you're done with map view; you can complete the rendezvous using only the NavBall.

Notes:

- Rule of thumb is that you want your speed relative to the target in m/s (which is what shows on the NavBall speed indicator when it's in target mode) to be about 100x less than your distance from the target in meters. So at 20km, you want to be approaching the target at about 200 m/s. If you go much faster, you can lose control of the situation, particularly if you're not used to rendezvous. If you go much slower, you will get very bored.

- When you are 20 km or less from your target, you should be able to see an indicator showing its position and relative distance when you are in vessel view (i.e. not map view.) You need to be able to see this unless you're using Engineer Redux or MechJeb to display target information.

- The pink circle marker on the NavBall represents the direction of your target, i.e. if you point your vessel's nose at the pink circle, it will be pointing directly at the target. The goal of a rendezvous is to have your prograde indicator sitting on top of the pink circle (and likewise, your retrograde indicator should be sitting on top of the pink cross.) This indicates that your ship is travelling directly toward the target.

- When you engage your engines, you are increasing your speed in the direction your nose is pointing. This has the effect of "pulling" your prograde marker toward where your nose is pointing. Likewise adding throttle will "push" your retrograde maker away from where your nose is pointing.

- So what you'll be doing is burning either near prograde to increase your relative speed or near retrograde to decrease your relative speed, while at the same time trying to keep your pro and retrograde markers pointed at the appropriate target markers. If you're burning near prograde you will be trying to "pull" the prograde marker onto the target circule and if you're burning retrograde (which is most of the time during a rendezvous because you're usually decreasing your speed as your distance to target decreases), you'll be "pushing" your retrograde marker onto the target cross.

3) So, say you get to 20 km separation and your relative speed is only 60 m/s. You want to burn prograde to increase your closing speed to 200 m/s. You do this by pointing your vessel toward a point on the opposite side of the target circle from your prograde marker. When you burn, you'll be dragging your prograde marker toward the target circle.

4) Once you've reached 200 m/s at 20 km, you'll notice your relative distance dropping pretty quickly. You'll want to turn your vessel around so you can slow down as you get closer. I readjust speed at 15 km, 10 km, 8 km, 6 km, 5 km, 4 km, 3 km, etc. When you're facing retrograde you want to burn with your vessel pointing on the opposite side of your retrograde marker from the target cross so you can push the retrograde marker onto the cross.

5) Once you get to within 1 km, you might find it interesting to switch to map view and notice how your orbit and the target's orbit have magically aligned.

6) Keep slowing until you get within 50 meters; you might have to turn prograde occasionally if you drop too much speed or if you get near the end and are going to pass too far from the target.

7) At 50 meters, you should be going 0.5 m/s relative to the target. Kill all of your remaining relative velocity by pointing straight at the retrograde marker (don't worry about pushing the marker at this point) and burning until your relative velocity shows 0.0 m/s. (If you're running MechJeb, you can zero it out to within 10 mm/s.)

Now you're ready to turn on RCS and start docking.

Edited June 27, 2013 by Mr Shifty

[Skorpychan]

My, you people are helpful. And wordy, too. I'll try and work through all that and hook my station together.

[WoodyD]

Wow, what a great thread. In this case "wordy" works. Some great perspectives and things to work on. Thanks to all.

[Guest Aaack]

Here's a very noob question from me which is related to this thread (I swear!)

I read that you can use RCSs to do some vector impulse, but all I can do with them is rotations. How do I set them up to translate instead of rotate?

Thanks in advance!

[Sirrobert]

The default keys for translate are IJKL, and for forward and backward H and N

[Guest Aaack]

Damn!, thank you very much Robert!

[Sirrobert]

Remember to switch to Chace camera, so the top of the screen is actually the top of the craft

[Skorpychan]

Okay. Which way do I burn at ascending and descending to change inclination?

[Tw1]

Test with a purple maneuver node handle. Whichever requires the least.

Edited June 30, 2013 by Tw1

[Kosmo-not]

Okay. Which way do I burn at ascending and descending to change inclination?

You burn anti-normal at ascending nodes, and normal at descending nodes.

[Sirrobert]

Okay. Which way do I burn at ascending and descending to change inclination?

Set a manouver node at the node, pick 1 of the 2 options and drag. If it's the wrong option, pick the other one