Noob Question: how to Rendez-vous?

[Augustulus91]

Hi, i have been playing kerbal for some time now (2 weeks) , it took me almost more than a week to build a craft and bring it in succesful Orbit. Luckily, my skills have progressed since then, and i am currently doing my first try at an Rendez-Vous.

So i have the second ship in close orbit to the other one (difference of 10km in Orbit height), and set the first ship as target. Which shows me the two possible encounters, with as minimum distance a bit more than 300 km.

So what do i need to do at these points? In which direction should I burn, and how can i speed up my craft along its orbit, so it reaches the first ship?

I have read the tutorial on the wiki, but i am a bit lost still.

Could any veteran help this little noob out? It's much appreciated!

Greetings!

[RoboRay]

A lower orbit is a faster orbit. So, if your target is ahead of you, you need to be in a lower orbit to catch up. Likewise, if your target is behind you, you need to switch to a higher orbit so it can catch up to you.

You don't have to lower or raise both sides of your orbit, just one side, then watch the closest point of approach markers. If you are getting 50km closer each orbit and your target is 300km away at the approach, you'll rendezvous in six orbits. You can adjust your orbit higher or lower to speed that up or delay the rendezvous (waiting for daylight at the rendezvous point, maybe).

When you get to the point where you're passing within a few kilometers of the target, make sure your NavBall is in Target Mode and point at the yellow retrograde mark (which now shows your motion in respect to the target). Burn the engines until it shows zero m/sec. This matches your orbits closely enough that you won't zoom past and fly away.

From there, point directly at the target and thrust a little bit to start drifting toward it. Don't build up too much speed. If you start to drift off course (and you will, starting from several kilometers away), you can steer back toward the target with RCS or by turning 90 degrees to use the main engine.

When you get within 100m or so, point retrograde to zero your relative velocity again. You are now rendezvoused.

Edited May 6, 2013 by RoboRay

[Augustulus91]

Thank you so much!

[Augustulus91]

Do you mean the pink retrograde marker instead of the yellow one?

[Augustulus91]

I have tried, and now my seperation at the next point is 7km , at the next it will be bigger, because i will have surpassed the first station.

I tried retrograde burning (at the pink triangle) , first my velocity to "target" drops at 110 km/s, but after that it increases again.

In some way, i can never really catch it.

So, i am closing in on the intersection, (still 2minutes away), i start retrograde burning, (the seperation at the intersection lowers), but my "target" speed increases to 150 km/s and beyond (and it's draining all my fuel, before i can put it to less than 5km seperation).

[Noticeably FAT]

You're pointing it the wrong navball indicators

Pink circle: Points directly at the target

Pink triangle: Points directly away from the target

Yellow circle with three lines outside the circle: Prograde marker (increases relative velocity, can be set to display rV for Surface, Orbit or Target)

Yellow 'crosshair': Retrograde marker (decreases relative velocity, can be set to display rV for Surface, Orbit or Target)

Blue 'crosshair': Maneuver node

[RoboRay]

Do you mean the pink retrograde marker instead of the yellow one?

No. The retrograde marker is yellow (well, it can be green if your monitor color settings are off calibration). The purple/pink markers are the ones that show the direction to your target, not the direction you're moving.

In Target mode, the prograde and retrograde marks do not show your orbital direction around the planet; they show your motion in respect to the target. If the prograde marker is right on the target marker, you're moving straight toward it. To take up a near-stationary position in respect to the target, point retrograde and burn until the speed shows zero.

Edited May 6, 2013 by RoboRay

[hapaxLegomina]

My usual tactic is to put the two ships in as different (but co-planar) orbits as the situation allows without wasting too much delta-V. That means if I'm rendezvousing with a ship in orbit about another body, I make sure to make my capture higher or lower. If the other vessel is already in Kerbin orbit, I'll try to stay as low as I can. With a wide difference in orbits, you spend more dV to rendezvous, but you get a window every orbit or two.

Transfer windows occur when one vessel will pass the other within that orbit. As soon as that magical transfer orbit begins, you have about half an orbit to find a solution. All you have to do is create a maneuver node with prograde or retrograde dV that will push either your AP or PE to the exact height of the other orbit. By sliding the node forward and backwards in time, you can find the precise location to do your transfer burn. If your target's orbit is circular, you can set the prograde dV once and leave it as you look for a solution. If the target's orbit is more eccentric, you'll have to fiddle a bit more, but it's not hard at all to get a rendezvous that's within half of a km, as long as your orbits are co-planar. Set another node to match speed and you're gonna be close enough to ignore orbital mechanics!

MechJeb 2.0 is far too useful for this. If you customize an info window, you can see closest approach distance and time to closest approach at a glance. This makes it super easy to know when you've got a transfer window, since MechJeb only looks at a single orbit. If the time to closest approach equals orbital period, you don't have a window this orbit.

[hapaxLegomina]

I have tried, and now my seperation at the next point is 7km , at the next it will be bigger, because i will have surpassed the first station.

I tried retrograde burning (at the pink triangle) , first my velocity to "target" drops at 110 km/s, but after that it increases again.

In some way, i can never really catch it.

Click on velocity until you've selected Target. When you're close, burn towards the yellow retrograde marker. You'll slow your velocity relative to the target. Burning towards the pink retro marker just burns directly away from the target. Remember, pink is direction, yellow is velocity. If you're moving straight toward or away from the target, yellow and pink will line up, but most of the time they won't.

[Deadpangod3]

Try putting your orbit almost exactly the same as the ship your trying to get to, but have it either a little lower or higher, you should get to it eventually and be very close to it (costs more fuel I think to match the orbits the right way) I do this sometimes when I'm trying to get to a moon or something, cause your garrenteed to encounter it eventually

[Augustulus91]

I will try this!

So the meaning of the yellow prograde/retrograde marker shift if you change your velocity-mode (orbit/target/surface)?

If so,

What's the difference between orbit and surface? (i mean, in the meaning of their grade-markers)

Anyway, thank you for your advice, this is a great community!

[Noticeably FAT]

The pro/retrograde markers tell you one (very important) thing: where you should point your ship to increase/decrease your relative velocity to whatever you have it set to display (Surface/Orbit/Target). Surface is measuring your rV from the surface of whichever body you are in orbit around, Orbit is measuring, well, your orbit. The best way to see this is action is to toggle between the two immediately before and after you launch your ship. While you are on the pad your surface rV is 0m/s (you aren't moving relative to the surface), but because you are moving with Kerbin you already have a certain amount of orbital velocity (I can't remember the value offhand). Immediately after launch if you toggle between the two you'll see that the Surface prograde marker is straight up (the direction that will best increase your rV), while your Orbit prograde marker is off to the east (the direction that will best increase your orbital dV).

Please note that I've simplified this somewhat (rocket scientists please forgive me), but I don't think overly so.

ETA: A little more clarification. The surface rV seems to be measured from the point on the surface directly underneath your ship, so while a rocket's prograde marker is likely to read close to straight up, that's not the only possible direction. A spaceplane in flight is likely going to have its prograde marker pointed closer to the horizon.

Edited May 6, 2013 by Noticeably FAT

[Augustulus91]

After some wobbling about, i achieved docking after one hour! Thanks everybody for the advice (once again )

[Fyrem]

well done!

the next time will be easier.