Docking Question?

[srbbnd]

I have been avoiding docking since I got this game, I finally have a stranded Kerbal in orbit. I have figured out how to match the orbit and get to the target. However, what I can not seem to figure out is on the tutorial it says to keep the prograde matched with the target on docking. After numerous attempts and the stranded spacecraft not having any thrusters I can never seem to get the prograde matching the target and always end up hitting the wrong place on the spacecraft.

Is there something I am missing, I can't seem to wrap my head around what direction I need to be going to manipulate the prograde to match the target?

Thanks!

Edited May 21, 2015 by srbbnd

[StuntMax]

The stranded craft may not have thrusters, but it may have reaction wheels.

Navball in "target" mode, approach the stranded craft, kill relative velocity, then switch to it, roll around so that the docking port faces your rescue ship, engage SAS if available, switch back to your spaceship, give a gentle push forward et voila le docking.

If the target is as dead as a brick and can't even rotate, it's trickier, you have to fly your rescue ship in front of the docking port, stop, turn towards it and push forward. A plugin showing the target docking port orientation (such as navball docking port alignment indicator) may come really handy.

[KatzOhki]

If you provide thrust on the opposite side of the target vector, it will pull prograde towards it.

o     O     x
^
|
prograde
       ^
       | target
              ^
              | thrust here

(just a general idea to help)

[Slam_Jones]

Burning prograde (forward) at your target will "pull" your heading (the direction your ship is actually moving) towards the direction you are facing.

Burning retrograde (backward) away from your target will "push" your heading AWAY from the direction you are facing.

Hope this makes at least a little sense.

[Snark]

Docking steps:

0. make sure that you and the target have compatible docking ports

1. Rendezvous with the target so you're nearby and at zero relative velocity

2. Maneuver around (usually with RCS) so that your docking port is lined up with the target's

3. very gently accelerate towards the target, very slowly (best to keep your relative velocity under 0.3, reduce to 0.1 when you get close)

4. Dock!

I'll assume that you've got 0 and 1 covered, and that your issue is with #2 and/or #3?

Couple of things that help with that:

- after step 1, click on the target's docking port and choose "Set Target", to make sure that you're tracking the docking port itself and not the target's CoM

- click on your own docking port and choose "Control from Here" so that your navball indicator is based on your docking port and not your command module

To be properly lined up for docking, you need two conditions:

A. you're aligned correctly (i.e. your docking port's axis is precisely parallel to the target docking port's)

B. you're positioned correctly (i.e. the lateral offset from your docking port's axis to the target's is close to zero)

The stock game doesn't give you much help with condition A; basically you just have to play games with the camera and look from all angles to make sure you've got it right. A very helpful (and lightweight) mod for that is Navball Docking Alignment Indicator, http://forum.kerbalspaceprogram.com/threads/54303. It adds a red icon to the navball indicating the correct alignment (it pops up whenever your target is a docking port). If you rotate so that it's centered, your alignment is good.

As for condition B, that's just a matter of "the target indicator on the navball is centered on your crosshairs", so you can use lateral RCS thrusting to adjust that.

Hope this helps!

[mrklaw]

Or unless the contract requires it, just get close then switch to the other craft and have the crew EVA across to yours.

is there a trick with RCS to know when right is right from the camera view? I.e. Pressing J will translate you to the right. Is that what 'control from here' on the docking port helps with?

Edited May 19, 2015 by mrklaw

[Superfluous J]

[Alistone]

You really need to use RCS translation for docking. In the bottom left hand corner there are different input modes. The top one is rotational where it changes which direction your ship points when you press w/s (up/down), a/d(left/right).

In the bottom left hand corncer there is if you press the middle button below the top one it puts you into "translational" mode where w is forward, s is backward, a is slide to the left and d is slided to the right. Shift is slide up and control is slide down.

Using the rotational point your ship at the pink target circle. Engage SAS (and RCS and I usually disable my engines so I don't accidentally throttle them up). Switch to translational "docking" mode and then press the "w" key and your RCS will push your forward and your yellow prograde vector should appear. Using a/d and shift/ctrl you can see that they directly change your prograde vector on the nav ball. This makes it very easy to line up perfectly with the port you are targeting.

Briefly using time warp to kill any rotation can help. (just tap up to 5x and back down to 1x using the "." and "," keys). But you may have to switch back to the other mode to point your docking port back in the direction of the target. Also, you may have to turn off SAS to allow your vessel to completely dock if they are't lined up perfectly at first.

[mrclucks]

I'm still pretty new but here's my .02

Assuming you have RCS in all the right places and you're very close to the traget, you want to initially get your prograde vector pointed "forward/front" and carefully adjust using translational controls so prograde and target vectors are in the same place on the navball. Go slower rather than faster since you'll be more precise and save a bit of RCS, and you're less likely to go flying past your target.

YouTube should have plenty of tutorials and all of them should be good regardless of the version

[srbbnd]

HA HA! Success! Thanks for the help. All good information. What really helped was the information targeting the opposite side to get the prograde in the target and video three. I still ended up retrograding quite a few times after a few passes but eventually got it. One last question that I can't seem to figure out is how do you internally transfer the stranded crew from ship to ship? I ended up just EVAing but that was a little stressful.

Thanks again.

[mrklaw]

If you have 'control from here' set to your docking port, and the target set as the other ship's docking port, and relative speeds at zero - then shouldn't RCS pivot you around the target docking port? I'm sure I've seen a video demonstrating that. So the difficult part should be getting the rendezvous nailed

[Snark]

One last question that I can't seem to figure out is how do you internally transfer the stranded crew from ship to ship? I ended up just EVAing but that was a little stressful.

1. Click on a crew hatch, so it brings up the little UI list of all the kerbals therein.

2. There are a couple of buttons next to each crewmember, "EVA" and "Transfer". Click "Transfer."

3. All the parts on your (combined, docked) ship with crew capability will light up: red if they're full, blue if they have space available.

4. Click on the blue-lit part to which you want to transfer.

Ta-da!

[Jaeleth]

Ships will always tend to rotate around their CoM, not the docking ports, what you can do is:

1. Make sure ship A and B relative speed is zero.

2. Switch to ship A, select ship B as target.

3. At navball controls select "Towards Target" orientation, wait for maneuver to complete.

4. Switch to ship B, select ship A as target.

5. At navball controls select "Towards Target" orientation, wait for maneuver to complete.

Now both ships have their docking ports aligned (almost, there are always deviations unless ships have low mass.

Select the most nimble ship (usually the ship with the least mass) and use RCS, docking mode, to approach, making small corrections along the way until docking.

Final docking speed should be kept near 0.2 m/s, keep rotating view 90 degrees around the ship (directly sideways and directly up) to validate alignment during docking maneuver.

[KatzOhki]

As Snark said, you click on the crew hatch to do a transfer, but you have to be docked together or capture it with the claw. Otherwise EVA is the only option.

[cicatrix]

This may be not what OP had in mind, but having The Klaw on your ship can save you time and monopropellant ))) A Klawed vessel is treated the same way as docked. And you don't need to worry if you have a compatible docking port, you might not have one at all.

[srbbnd]

I feel like a million bucks, and an idiot. I kept alt right clicking the hatches. Not just left clicking the hatches but everything is sorted. Thanks for all the help. Much more helpful community here than some others.

Thanks!

[StuntMax]

If you have 'control from here' set to your docking port, and the target set as the other ship's docking port, and relative speeds at zero - then shouldn't RCS pivot you around the target docking port?

Wherever you "control from" doesn't change a bit.. RCS always rotate you around the COM of the ship, and also they always translate you a bit unless the torque from the RCS is perfectly centered on the COM.

SAS can dampen this effect (and try to make you rotate around the component you are "controlling from"??? Not sure about this), but it does no miracles if your RCS thrusters are badly placed. Surely it can't make you rotate around a target....

[mrklaw]

Wherever you "control from" doesn't change a bit.. RCS always rotate you around the COM of the ship, and also they always translate you a bit unless the torque from the RCS is perfectly centered on the COM.

SAS can dampen this effect (and try to make you rotate around the component you are "controlling from"??? Not sure about this), but it does no miracles if your RCS thrusters are badly placed. Surely it can't make you rotate around a target....

had to dig around my youtube history to find it. Turns out he is using an avionics thing or a high XP pilot and enabling target tracking. Looks helpful for docking?

[SanderB]

Once your vessel is roughly in front of the target docking port, do a "Control" from from the target docking port and note the orientation shown by the navball. Then go to the main vessel and use translation (or if you know how, use main engine thrust) to move the docking port target marker on the navball in the opposite orientation . if docking port is facing due east, put the docking port target marker on the main vessel due west using translation. Once the docking port is in the correct orientation, it should be a simple task to dock. You can also use the anti-target marker by pushing it into the same direction as the docking port using the "control from" option in the right click menu.

Demonstration video.

[moronwrocket]

Crew Manifest is a nice mod for swapping Kerbals around connected vessels. Sometimes the click areas for hatches don't work, and/or are hard to find.

[Kerbart]

Boarding the destination craft is easier when you align it with the N/S axis of the planet (ie pointing to normal/anti normal in a 0° inclination orbit, which all rescue missions seem to be)