Docking? How do I get two crafts near each other?

[DaElite101]

I tried the tutorial but I couldn't understand it quite well. I don't know how to get two crafts near each other for docking, and seeing that I get stuck on the "Go prograde until your orbit crosses the stranded ship's orbit" or something, I'm likely doing something wrong. I can't even tell if the two orange markers are within 5km of each other. So, can you explain this in a simpler way?

[Rocket In My Pocket]

Keep this handy visual guide open and alt tab back and forth, following each step one at a time (I always forget who the heck made this): http://i.imgur.com/zAxhwQ5.png

Spoiler

Here's another version of the same guide that seems to have more information, I learned using the one pictured above but this seems just as good if not better: http://i.imgur.com/h1QMVsT.png

You can ignore the bit about the docking port mod, I've never used it personally. Once you are close enough to see your target, you shouldn't have too much trouble docking them together by eyeballing it. Just go slowly and carefully. Any other questions, please ask!

Edited July 2, 2016 by Rocket In My Pocket
Added link to alternative guide.

[Aegolius13]

It's a tricky process that definitely takes a while to master.  You might want to check out some videos (Scott Manley has good stuff).  

Making your orbit overlap with the target's is part of the process, but you also have to make sure both ships are in the overlapping orbit at the same time. There are a couple ways to do this- one is simply by waiting until the two ships are at the right places in their respective orbits.  For example, suppose you're in an orbit further from Kerbin and looking to rendezvous with a ship closer in.  The further-out ship takes longer to make one orbit.  So if the two ships are on opposite sides of the planet, just wait a few orbits and the closer-in, master-moving ship will "catch up."  

One the ships are in approximately the right place, it's just a matter of fine-tuning - both by changing the maneuver itself, and moving the time you start it (i.e., dragging the node back and forth).  If you keep iterating, you should get to a point where the orbits are pretty close.  You can see the minimum distance between two ships by holding your mouse over the little  "closest approach" arrows.

Also, if your orbits are inclined, you can either (1) match planes beforehand by burning normal or antinormal at an ascending / descending node, or (2) put a normal/antinormal component into your rendezvous burn so that the ascending / descending note is right at your rendezvous point.  

Once you get the basics down, the next challenge is to rendezvous so that the relative velocity between the two ships is as low as possible at the rendezvous point (meaning you'll use less delta-v matching speed).  This is generally accomplished by making sure the two orbits are tangent, rather than having one cross another.  

One side-effect of all this stuff is that it's easiest to rendezvous from two concentric, circular, plane-matched orbits.  It's easy to get a good tangent intercept by moving the manuever node back and forth to hit the right spot in time.  

Above all, though, it just takes a lot of practice, but will soon become second nature.  

 

 

[Streetwind]

43 minutes ago, DaElite101 said:

So, can you explain this in a simpler way?

 

Explained in a simple way: imagine you're going to the Mun.

The main difference is that if you're going to the Mun, you are starting in a very tight, fast origin orbit, and you are going to a very wide, slow destination orbit. Meanwhile, in a typical orbital rendezvous, your origin orbit and your destination orbit are going to be of similar speed and size. But in terms of what you must do, the two exercises are identical: first, make a burn so that you get an encounter (signifying that both you and your target are in the same location in space at the time of crossing orbits). Then, make a second burn at your encounter to "capture". In a rendezvous, the "capture" is actually the act of matching velocity with the target. It's still just one burn though, just like the capture burn at the Mun.

Now, when you go to the Mun, you are doing so at a specific "alignment" - when the Mun is a certain angle ahead of you in its orbit. In a rendezvous too, you need to be in the right "alignment", or you can burn however you want, you are not going to get an encounter/close approach. This is, oddly enough, where many newcomers fail. They think that the timing of a rendezvous burn is some sort of arcane magic, that they must learn something completely new, when nothing could be further from the truth. But fear not, there is a simply method to pull it off, and all you need is a single maneuver node.

So to make your job as easy as possible, make your rendezvous as similar to a flight to the Mun as possible. This means: make sure that your orbits aren't already crossing. Make sure that your own orbit is fully inside that of your target's - that your apoapsis is lower than your target's periapsis. Then, make sure that your inclination matches. When you target something, the game shows you the "ascending node" (AN) and "descending node" (DN) markers - these are the points at which you can make normal/antinormal burns to match inclination. Hovering your mouse over the AN/DN shows you how many degrees you are off. Try to make sure that you are no more than 0.1 degrees off.

Once you have done that, all that's left is to figure out where to burn to get an intercept. Since you're inside your target's orbit, it must be ahead of you, just like the Mun. But because your orbits are similar in size, it must be only a small distance ahead of you, unlike the Mun. If the target is not a small distance ahead of you, just timewarping for a while will fix that, because you are in a tighter orbit and thus move faster. You will keep catching up on it with every turn around the planet, until it is only a small distance ahead of you.

At that point, make a maneuver node. Give it some prograde dV - enough to push your apoapsis just a little bit beyond your target's orbit. Now, click and drag that maneuver node around in front of your craft. Are you getting close approach markers anywhere? If no, maybe your target isn't close enough yet. Timewarp for one extra loop around the planet and try again. Repeat until you get close encounter markers - or until you pass your target. In which case you know that you were already too close by the time you made your first try. You'll have to timewarp until you are once more approaching your target from behind.

If you get close approach markers - great! Keep dragging that node until you get the closest encounter that you can, and if necessary, add or remove some prograde dV. Mousing over the close encounter marker will show you just how close you are when it becomes visually difficult to discern the marker's behavior. Note that if you cross the target orbit twice as opposed of just touching it in one spot, you can get close encounters on both the first crossing and on the second crossing. Pick one of the two. Both are equally valid, but don't try to line up both at the same time. It is both impossible and redundant. As a rule of the thumb, any close approach of 2 kilometers or less is good enough, though of course the closer you get, the better.

Execute your node. Verify that you are still going to have a close approach of 2 kilometers or less - if not, make a new node and correct. If everything is in order, switch your navball into "target" mode, and warp forward to you close encounter. When you reach the minimum separation distance, find the retrograde marker on your navball (which, again, should be in "target" mode) and burn towards it until your velocity shows 0 m/s (or as close to it as you can go). Congratulations, you have just matched orbits with your target, and your rendezvous is complete. Simple as that.

If you still want to go closer - just point your nose at the target and thrust forward. As long as you are closer than 2 kilometers, this will work without much in the way of error. You can always become stationary next to your target again by burning retrograde in target mode.

Edited July 2, 2016 by Streetwind

[bewing]

The orange and magenta intercept markers are supposed to be your biggest tools when creating a close approach. Unfortunately, they have been much buggier than usual in versions 1.1.2 and 1.1.3.

It all comes down to a couple simple things. If you have two ships in orbit, then the ship in the lower orbit will move ahead of the ship that's in a higher orbit. This is the main fact that you take advantage of to create a close approach. If the target ship is behind you, then you want to be in a higher orbit. If your target ship is ahead of you, then you want to be in a lower orbit than it is -- if possible. The problem with being in a lower orbit is that the atmosphere is down there, so there is a strict limit on just how much lower you can go (but there is no limit on being higher).

If the difference in orbital heights is just a few kilometers, then the lower ship will only gain maybe 5 kilometers per orbit on the high ship. So if you have 1.3 million meters to catch up, then it may take a very long time if the two orbits are near each other.

If you select the target ship as a target, then you can hover your mouse over the ship and it will tell you the relative distance. If you hover over one of the orange or magenta markers, it will tell you what the distance will be when the ship reaches the marker -- or at least it's supposed to. But the point of the markers is supposed to be that they will tell you what will happen one orbit from now while you are burning to adjust your orbit. So you stop burning when the marker you are looking at says that the distance will be less than a kilometer or so.

[klesh]

Its very telling, these diagrams, and "getting it".  Once you do get it, it all makes sense and is easy to do, but trying to read about it without being in a classroom and having someone to bounce questions off of makes it far more difficult.   Imagine trying to write out step by step instructions for driving to the store for a cup of coffee.  You'd include minutia that becomes automatic to your brain after you know how to do it.  (If parking spot <A> is taken, proceed radially until you reach parking spot <B>, etc)

 

It clicked for me by watching Manley do it.  

Edited July 3, 2016 by klesh
This website is an absolute chore on mobile. I miss the old forums.

[DaElite101]

Thank you all for the explanations! The diagram really helped too!

[Hotel26]

I found the following was the last piece in the jigsaw that unlocked those occasions in which I still got stumped; it's definitely only one trick in the armory.

If you have two craft in circular orbits with fairly close inclination, I use Kerbal Alarm Clock to tell me how long and how many orbits to the nearest approach.  They don't have to be close orbits and, in fact, more distant orbits provide faster opportunities.

Then I look at my orbital period: say it is 40 minutes.  So then I set a Nearest Approach alarm to go off 40 minutes before the event.

When it goes off, that means that sometime in the next orbit will be the time to execute a Hohmann transfer to the target orbit.  Set up the maneuver node and then drag it around the orbit ahead of the craft until the intersection markers are closest.  Then execute that node.  Set another alarm for the newest Nearest Approach which ought to be within a few kms.  Target mode retrograde at that nearest distance to cancel target-relative velocity.  You're ready for final approach which is gonna be a bit like Putt-Putt.  (Or more advanced, "fly the ball".)

If your orbits are too close or too many phasing orbits apart, Nearest Approach may not find one.  In that case, radically change your craft's orbit altitude.  Higher if you are in front of the target.  Maybe lower, maybe, if you think you are not too far behind.  Higher will always work, eventually, but may use more fuel than necessary.

You'll figure out the fine details later.

Edited July 16, 2016 by Hotel26
typo

[Diche Bach]

So I think I finally figured out what those little squiggle marks in the NavBall mean in dock mode . . . wow. So cool.

Managed to get this destroyer sized rocket lined up with a fairly large unmanned probe (the start of Kerbal Space Station) . . . so cool to use that NavBall magic to swing it from an orbit 9km out of whack into a more-or-less precisely lined up deal then cancel out all motion at ~5k, then slowly cruise in. So easy to control really once you get it, except for one thing: with RemoteTech running, probes that are not under control seem to go drunk and are seemingly impossible to dock with while they are not in radio contact. Just slightly annoying as having antennae on both the incoming manned, and the target unmanned would presumably allow the pilot in the incomer to align the target. I guess I'll just give myself a 'pass' and turn RT off when I approach unmanneds that are out of network.

[Tyko]

On 7/2/2016 at 10:50 AM, Streetwind said:

 

Explained in a simple way: imagine you're going to the Mun.

<SNIP>

Now, when you go to the Mun, you are doing so at a specific "alignment" - when the Mun is a certain angle ahead of you in its orbit. In a rendezvous too, you need to be in the right "alignment", or you can burn however you want, you are not going to get an encounter/close approach. This is, oddly enough, where many newcomers fail. They think that the timing of a rendezvous burn is some sort of arcane magic, that they must learn something completely new, when nothing could be further from the truth. But fear not, there is a simply method to pull it off, and all you need is a single maneuver node.

<SNIP>

This has been a continuous process for me. going from an orbit, to an encounter with Mun, to rendezvous, on to my first transfer to Jool local space - this idea that it's all using the same mechanics and only the scale is changing.

[Diche Bach]

Bit more success for me, and I feel like I've passed the "second" watershed of mastering docking: being able to just send up a ship, and dock it with the space station that day, with only minimal hassle.

Kerbal Space Station is coming along now with four modules in place

In order of deployment

1. is the central unmanned part with the large disk of static solar panels. Basically a comms satellite with the tech I had at the time and plenty of solar potential.

2. the majority of the central section: deployed with an aft command module similar ones still docked behind modules 3 and 4 (on the port and starboard forward bays). This contained living space, a science lab, lots more science gadgets, plenty of batteries, and way too many hydrazine spheres (regretting my excessive use of these now that I have the KW cylindrical ones which can be tweakscaled . . . that many seems to lag the thing pretty bad).

3. is in the right foreground of the image, more living quarters, more fuel storage, etc.

4. (which actually arrived before 3 even though it launched a week later!) is an agronomy module

5. will be a training academy and at that, I may just leave it. It lags noticeably now, but the nice consequence of this is: it actually seems to make docking easier!

The main thing I've learned (and which the very good, but brief tutorials didn't address): The single most important part of docking is the burn when you go from your initial parking orbit to extend your apoapsis into the altitude of the target: this MUST be "timed" properly.

If this burn is timed properly and properly executed, everything else is frankly a cake walk. If this is poorly timed or improperly executed, everything that follows will range from challenging to damn near impossible without switching to an orbit at a different altitude and then retrying.

If one intends to use a "prograde" approach, then one MUST plan that "rendezvous" burn so that one will be retrograde to the target, and within a reasonable distance/speed difference. This can requite a great deal of fiddling with the flight planner and checking maneuver nodes at various future dates in various positions, but once you get the idea of it, it is not that hard. But if you don't "get" this then it seems like magic.

If that burn is done properly, literally you need like a few kilograms of hydrazine, and a bit extra of main fuel to either accelerate or decelerate. You just get the burn to the ideal rendezvous (~5km but not too much less seems good, and nothing more than 150m/s speed difference [and ideally it seems with a "negative" speed difference, meaning the incoming vessel will be slower than the target vessel at the time of the rendezvous . . . the other way makes it more tricky by requiring the use of LOTS of hydrazine to slow down, else whipping it back and forth between retro/prograde]).

When I've done it 10 times, I may well just let MechJeb take over, as for all its interest, it is inherently tedious, primarily because the flight planner interface is suboptimal. The fact that there seem to be no options to turn various displays on/off in the flight planner (no I don't WANT to see the goddamn apoapsis and periapsis right now, I'm trying to get the rendezvous planned! . . . if I'm just being a boob and it IS possible to minimize/turn off some of this junk in the flight planner window [the mission waypoints are a gigantic pain too] please, someone tell me so I can eat crow and be happy with a less tedious experience]).

 

[Hodari]

4 hours ago, Diche Bach said:

The main thing I've learned (and which the very good, but brief tutorials didn't address): The single most important part of docking is the burn when you go from your initial parking orbit to extend your apoapsis into the altitude of the target: this MUST be "timed" properly.

If this burn is timed properly and properly executed, everything else is frankly a cake walk. If this is poorly timed or improperly executed, everything that follows will range from challenging to damn near impossible without switching to an orbit at a different altitude and then retrying.

I wouldn't say the timing is quite THAT critical, unless of course you're using some sort of life support mod or something else which is imposing a time limit.  Otherwise, timing the burn correctly so that you get a close approach right away is obviously still better, but even if your timing is completely off and you wind up on the opposite side of the planet from your target, as long as your orbital periods are different and not in some sort of resonance with each other, you will eventually get a reasonably close encounter.  I've had times where I spent a few days timewarping around and gaining 1-200km per orbit on the target until I was finally close enough to make my final adjustments for the actual intercept(mostly because I didn't even bother to check the position of the target vessel before launching the other one).  It's not really challenging or impossible, just means a lot of extra waiting.

Either way though, congrats on learning to dock.

[AyeLmao]

In real life it depends on where you are, if you are behind the object you are trying to get to then lower your orbit then after several orbits it should bring you to it, if the object is behind you then burn Prograde a bit, then go around a few orbits until you get close, then make some final Adjustmens

[DD_bwest]

being able to bring your relative veloxity to near zero is vitally important.

next is knowing how to fly using your navball.  you can even dock in map view if you know how to read and fly by it

 

if they are in LKO and really close to the atmo edge.  its better to come in from behind so any burns towards target wont be also your retrograde,  brining you closer to that edge.

[Diche Bach]

2 hours ago, Hodari said:

I wouldn't say the timing is quite THAT critical, unless of course you're using some sort of life support mod or something else which is imposing a time limit.  Otherwise, timing the burn correctly so that you get a close approach right away is obviously still better, but even if your timing is completely off and you wind up on the opposite side of the planet from your target, as long as your orbital periods are different and not in some sort of resonance with each other, you will eventually get a reasonably close encounter.  I've had times where I spent a few days timewarping around and gaining 1-200km per orbit on the target until I was finally close enough to make my final adjustments for the actual intercept(mostly because I didn't even bother to check the position of the target vessel before launching the other one).  It's not really challenging or impossible, just means a lot of extra waiting.

Either way though, congrats on learning to dock.

I had exactly that "resonance" problem with my number 3 module.

Waiting for a better rendezvous while you are still in an orbit well below (or it could be well above) the target is one thing: waiting once you have your apo in approximately the same altitude range as them is another (or worse, have missed one encounter and then wound up raising your peri toward circularization). This was the main thing I learned: if the first try doesn't work, just go past, lower orbit (or raise) fairly substantially (not just a few kilometers, maybe 50 kilometers or at least 20. Start from the apoapsis "insertion" stage again, and try to get a good rendezvous by fiddling with the maneuver at that stage. Trying to correct a failed attempt without dropping and re-syncing the timing seems to ultimately waste more fuel (and cause more stress and risk more destruction) than simply letting a failed attempt pass and starting from step 3 or 4.

[DaElite101]

After trying out docking again, I finally did a rendezvous successfully and got a small refueling tanker near my SSTO. But it didn't have enough fuel. The next module for my Minmus mining station had plenty of fuel on hand, so I got the module near my spaceplane. However, it has no sideways control (As in, no going sideways without turning the ship) and all of the docking ports were on the sides. So I used the refueling tanker to transfer fuel over to the spaceplane. Still not enough fuel. So then I sent the module to Minmus, as planned. Now I'm sending yet another tanker to rendezvous with the SSTO, and I'm fairly sure I got the hang of it now. Thank you!