Docking, not rendezvous

[PetahSchwetah]

[deleted]

Edited January 14, 2024 by PetahSchwetah

[lajoswinkler]

Proper placement of RCS thrusters (away from center of mass) and proper mass distribution is the basic thing you need to do. Then jump into chase mode and you know the rest.

It might be a good thing to adjust one dimension at a time. Some people just thump against the keys, forgetting about Newton's laws and then they increase the distance or even crash into the target.

[T-Pilot395]

I just use normal mode, with chase camera from the docking port's view so the ship's orientation matches the camera. Use "Control From Here" on your docking port if you're doing side dockings. Other than that it is a loong, delicate process.

[capi3101]

I recommend keeping in Staging Mode - using WASD for rotation and IJKLHN for translation. Make sure you pack RCS on any part you want to dock, and that you take no fewer than twelve blocks - four at each end of the craft as far away from the center of mass as possible (for rotation torque) and four on the center of mass (for translation).

Alignment's generally the trickiest bit of docking; if you're not aligned on the target port, you're not going to dock. So what you do is move towards the target, zero out your speed when you get to the next checkpoint distance, realign (navball centered on the pink doughnut), switch to the other craft, align the port with your craft, switch back, rinse and repeat. Do that at 100, 50, 20 and 10 meters. Go slow; no faster than .5 meters per second when you're on final approach. Hopefully you don't have to do a realignment at five meters; that's too close for safe maneuvering of either craft in my experience. If necessary, back off and try again.

Alternatively (if you're into mods), install NavyFish's Docking Alignment mod; it's a snazzy tool and I HIGHLY recommend it (this from a guy who doesn't use that many mods in general).

[Vlk]

I usually just go close to the target, kill every velocity, align the two objects so the docking ports are looking at eachother. Then i set target to the target docking port, and go forward with 0.2m/s. You may want to use caps lock for small, precise rotations. With this method, you can dock without rcs, but its easier if you have rcs, and use docking mode to adjust your velocity so you go towards the target.

as lajoswinkler said, when you use rcs in docking mode, you have to make sure that the rcs thrusters are around your ship's center of mass. One additional note: if you burn fuel, your center of mass may change. To prevent this, it is wise to design your ship so the fueltank is exactly at the middle of the center of mass. This way it does not matter how much fuel you burnt, your center of mass will not travel away.

[Kasuha]

I am used to normal mode, but surprisingly I only use one set at a time, right hand on mouse to look around (chase mode) and switching left between IJKL and WASD if needed. Most important bit is always to orient the destination port to north/south (actually perpendicular to orbit, north/south for equatorial orbit) and my own port the other way, no changes to inclination are needed after that and the whole docking reduces to just hunting the target indicator with the prograde indicator on the navball using RCS. And of course checking with camera if you're still on the spot because if the target port is not in the target's center of gravity (which usually isn't) the navball may lead you to crashing to it from the side. Hopefully this bit will improve in next version.

[mellojoe]

Put a light source near the docking port. Makes it easier to see on those night-side trips.

Chase cam. Then use Q and E to rotate so that the IJKL are intuitive. For example, pressing J moves you to the left. Chase cam will keep it all relative as well.

SAS. Keep it on. The new SAS helps to overcome imbalanced RCS thrusters, which prevents you from adding needless unwanted rotations.

Control from the docking port you want to connect to/with. Point one craft North and the other craft South(0 degrees and 180 degrees). Again, it makes frame of reference much easier to decipher.

And then, YES, it just takes time, every time. You have to move so slowly (0.3 m/s) and patiently, that it just adds time to every docking. It all adds up like building a house. The better your rendesvouz, the better foundation you have. The better you know the Nav-Ball and how to manipulat it, the better structure you have. Getting comfortable with docking controls is just icing on the cake. [mixed metaphors for the win]

[M5000]

Proper placement of RCS thrusters (away from center of mass) and proper mass distribution is the basic thing you need to do. Then jump into chase mode and you know the rest.

It might be a good thing to adjust one dimension at a time. Some people just thump against the keys, forgetting about Newton's laws and then they increase the distance or even crash into the target.

I disagree with this. Seeing as you use RCS for mostly translation, not rotation, having RCS thrusters as close to the center of mass as possible. If you're using RCS to perform rotation, you need more reaction torque. You can perform a docking with remarkably low amounts of RCS if you use this method. I've done docking using like, 20 units on a 3-man capsule because I didn't use RCS for anything other than translation. Sure, if you place your thrusters evenly about the center of mass you can get more effective torque, but if you have any amount of respectable reaction wheels, you can use them for rotation.

However, I do agree with you that it's less about "How much distance" and more about "how much relative velocity". Remember, the only way to slow down in space is to impart a force in the opposite direction in which you are moving, usually by means of monopropellant RCS thrusters or your bi-propellant main engines.

When you're docking, there's usually two situations you'll be in, more likely than not.

1: Two small craft docking 1-to-1.

2: A craft of some undetermined size, is to dock to a large craft that is immobile.

In situation 1, docking is really an effort on the part of both ships involved. First, when you get close enough to begin moving on RCS only, foregoing your main engine, switch to your target's craft. It's at this time you'll need to prepare the ships for close encounters. First, kill out your relative velocity to the target by burning retrograde with the navball in "Target" mode. Find the ship that will be docking to this target somewhere in space. Point the docking port you're going to want to dock with toward the ship you'll use to dock, so that it's already lined up for approach. Now is also the time to retract any extremities that may be vulnerable or risky to move around, such as solar panels, as well as turning on any lights that may be intended to help you find the craft's position in space. Once you've prepared your target for the final approach, switch back to the craft which you were originally piloting. Prepare it for docking as well, retracting solar panels if necessary and turning on your docking lights to see what you're looking at. (Not necessary, but VERY nice if you're on the dark side of Kerbin.) Attempt to set the actual physical port on the craft you're going for as a target, ensure the Navball is set for Target mode, and your camera to "CHASE" mode, line up toward that marker, and translate forward to begin the approach. Watch the navball. Try to keep your nose marker right on the pink symbol, as well as your prograde marker. If they drift apart (they probably will) simply use your translation up/down/left/right to move the prograde marker around on your nav ball. Yes, it is that easy. The prograde marker, at low velocities, will very responsively follow your IJKL keys, with H and N making it harder or easier to move, due to increased or decreased velocity. Simply keep adjusting, trying to keep your nose, prograde, and target-prograde all aligned, and you will eventually be close enough for it to simply engage. A final docking speed should be, ideally, no more than .1m/s, but .3m/s could be done safely as well. Once the magnets begin to engage, let the game take over. Disable your SAS and RCS systems immediately and as quickly as possible. The magnets will guide you into place.

In the second situation, where the target is not easily movable to face your position, you will need to get close to the large craft using the same basic method as above, but once you get close enough, say, about "one fully-extended Gigantor-XL Solar Panel"'s length away, then use your translation to move around the craft, just like a gigantic Kerbal EVA pack.

Hope this helps, once you figure it out, it's super easy.

[LameLefty]

My advice is just various combos of all of the above combined with this: PRACTICE! Launch lots of ships and targets and just practice. Dock. Undock, change orbits slightly, wait a few orbits and dock again. Repeat until comfortable.

Using the navball is key; everything you need is there and in the Map markers. One thing I'll add is that you do NOT need 12 RCS quads. What you need is RSC balancing, however many blocks that takes for whatever you're trying to maneuver. For a small capsule or probe-controlled stage or module, you might only need 4 quads; take a look at the layout of the Apollo CSM stack, for instance. For a long, heavy rocket stage you might need 8 (four at each end) or yes, maybe even 12. But it depends. Practice, practice and more practice and then is just "clicks" and becomes easy. Just remember to build your RCS layout with COM in mind and do it symmetrically.

[Technical Ben]

Here is a video example if it is of any help:

[lajoswinkler]

I disagree with this. Seeing as you use RCS for mostly translation, not rotation, having RCS thrusters as close to the center of mass as possible. If you're using RCS to perform rotation, you need more reaction torque. You can perform a docking with remarkably low amounts of RCS if you use this method. I've done docking using like, 20 units on a 3-man capsule because I didn't use RCS for anything other than translation. Sure, if you place your thrusters evenly about the center of mass you can get more effective torque, but if you have any amount of respectable reaction wheels, you can use them for rotation.

However, I do agree with you that it's less about "How much distance" and more about "how much relative velocity". Remember, the only way to slow down in space is to impart a force in the opposite direction in which you are moving, usually by means of monopropellant RCS thrusters or your bi-propellant main engines.

It does depend on the size of the spacecraft. I can't imagine rotating a huge ship fast enough just by torque. That is, if I want to do something in a reasonable amount of time. I could waste my time by doing everything slowly, but I don't want to.

The worst thing that sometimes happens to me at rendezvous and docking is when I run out of monopropellant and all I have is the main rocket engine. Technically, it is possible to dock like that, but it's very tedious. I either try to approach using the target itself or scramble the mission.

[csanders]

It's key to know how to set a port as a target, and the target mode navball.

1) when you're close (around 100-200m), target the other ships docking port (this will be called "ship 2", you are currently flying "ship 1").

2) make sure navball is in target mode. Point noise to retro vector, thrust (gently) until the speed is as close to 0 as you can get it

3) point craft at target.

4) use "]" and "[" to switch control to ship 2. EDIT: Make sure you click on the port you just targeted, and "control from here" /EDIT. Target ship 1's docking port, point at the target. When you are pointed, use SAS to stop rotation (or time warp for a split second - is that cheating??)

5) Switch back to ship 1. Thrust to about 2 to 8 m/s (depending how far you are, and how fast you can decelerate with RCS)

Both ships should be pointed at each other, and moving towards each other. NEVER ROTATE AGAIN FROM THIS POINT ON.

6) Now use IKJL to keep the velocity vector icon centered on the target icon. If the target icon drifts left from where you're pointing, translate left (don't rotate). Drifts right - translate right. etc. Don't use a lot of translation. How much translation?

O = velocity vector icon

* = target vector icon

v = where you're pointing

*Ov - this is not enough, the velocity vector is between the target and where you're pointing

O*v - this is about right. I try to keel the target icon equal distance between the velocity vector and where you're pointing.

O *v - probably too much.

When you're close, reduce speed to around .2m/s

Note: if you do what I did above, you could do it from the map view if you knew the distance the ships are apart (with the exception of targeting the ports)

Edited September 25, 2013 by csanders

[blizzy78]

I have made an in-game tutorial about docking, perhaps you might want to try this out. (see signature)

[mellojoe]

Also, learn the Nav-Ball and how thrust impacts the markers.

Thrusting prograde (toward) the target pulls the prograde marker toward where you are pointing. Thrusting retrograde (away) repels the marker.

[lajoswinkler]

Also, learn the Nav-Ball and how thrust impacts the markers.

Thrusting prograde (toward) the target pulls the prograde marker toward where you are pointing. Thrusting retrograde (away) repels the marker.

It's worth noting that thrusting towards the target will never pull the yellow prograde marker in the center. It will approach asymptotically, so you have to burn sideways. For example, if Y is yellow prograde, O is target and V is center of the navball, and you've got OY, burn VOY until Y comes in the O.

[PetahSchwetah]

[deleted]

Edited January 14, 2024 by PetahSchwetah

[Apollo13]

1. Use Docking mode versus Staging mode. It's more intuitive given that you're already used to it. I've also programmed a mouse button to switch between rotation and translation to change quickly.

2. Install Docking Port Alignment Indicator.

[Kulebron]

I just learned how to rendezvous and how to dock. But I still have some problems with the docking controls. I have managed to dock 5 parts into a space station, but it took me 10-15 minutes to dock each part. I know the rendezvous part, that is easy, but to dock is the problem.

So, what controls do you recommend? Docking mode, or not? Any specific key bindings?

Thanks!

I'd second the recommendations to use WASD and IJKLHN (although I use UIOJKL with U and O for forward and backward). RCS ports have to be around the center of mass, to not turn the ship when you translate it. And a good idea is to switch between ships and align them at each other's docking port (right-click at own port to control from there, right-click other's port to make it a target).

Another trick is to point one ship's port in some direction you can remember (say, horizon north), and aim the opposite in the other ship. (Horizon south, 180 degrees) then translate without turning to match the target marker at your pointer and forward.

[Mr Shifty]

2. Install Docking Port Alignment Indicator.

This. IMO, if you're not using the DPAI, you're doing it wrong.