Docking questions

[hhatch]

Well thanks to the success of "Operation Quick Save" I was able to get back to Kerbin in one piece from the Mun. Now, like a fool I decided to tackle docking and have a number of questions.

 

When doing a maneuver to create the 2 sets of intercept points should I always use the orange ones or can I just pick the set with the closest separation  ?  Also, It takes me a long time to get near my target. If I take too long I assume the separation distance becomes greater. Does this make it more difficult to dock ?

 

I've had some difficulty getting a good burn to adjust my inclination to the target. This morning I did many burns and the inclination was almost always off by .1 degrees. I finally redid the maneuver node even though the one before was at 0 degrees and I hit the burn first time. Is there some trick I'm missing ?

There are times when I'm getting close to target that I cannot use the shift key to do a slow burn. I can use X only. There are also times when the retro and prograde options are not available on the navball.

 

I've gotten pretty good at getting close to the target burning toward the target then zeroing out velocity. Using RCS mode has been hard.  Things get screwed up when I try and close the deal. It seems like all of a sudden the target will zip by and then start moving away from me. I've actually gotten within 10 meters but then I usually crash.

 

I'm going to put plan B into operation. I'm replacing mono propellant with beer.

 

[Plusck]

41 minutes ago, hhatch said:

Well thanks to the success of "Operation Quick Save" I was able to get back to Kerbin in one piece from the Mun. Now, like a fool I decided to tackle docking and have a number of questions.

 

When doing a maneuver to create the 2 sets of intercept points should I always use the orange ones or can I just pick the set with the closest separation  ?  Also, It takes me a long time to get near my target. If I take too long I assume the separation distance becomes greater. Does this make it more difficult to dock ?

You can use either set, whichever is closest. However, the real answer is probably more like "neither"... because if you do the right job of "pushing the marble" as you approach the first orange set, you'll end up with the intercept point being somewhere between the two. I'll explain a bit further down the page...

And this shouldn't make any difference to the difficulty of docking.

45 minutes ago, hhatch said:

I've had some difficulty getting a good burn to adjust my inclination to the target. This morning I did many burns and the inclination was almost always off by .1 degrees. I finally redid the maneuver node even though the one before was at 0 degrees and I hit the burn first time. Is there some trick I'm missing

The main "trick" is just to do about 95% of your burn at normal thrust, then delete the node and finish up the burn while watching the map view at minimum thrust. You should see the chevrons get closer and AN/DN drop to zero.

The next trick is to fine-tune using RCS keys IJKL-HN. When finishing the burn, as soon as the chevrons and/or AN/DN start getting further from what you want, stop immediately. Turn on RCS and use "N" to reverse thrust. Then try each of the directions IJKL in turn to see which one(s) you need to bring the chevrons and AN/DN down to where you want them.

52 minutes ago, hhatch said:

I've gotten pretty good at getting close to the target burning toward the target then zeroing out velocity. Using RCS mode has been hard.  Things get screwed up when I try and close the deal. It seems like all of a sudden the target will zip by and then start moving away from me. I've actually gotten within 10 meters but then I usually crash.

This is where you really have to learn to "push the marble". And keep your eyes on map view all the time. RIght-click on your target and on the orange chevron so that they both show up and you can see (a) distance to target, (b) time to intercept, and (c) distance to target at intercept.

Then don't do anything until you're a minute or so out (unless relative velocities are in the hundreds of m/s, then start earlier).

At one minute from intercept or so, turn to target retrograde, look to see where the anti-target (pink upside-down Y) is, and thrust on the other side from prograde. On the NavBall, your markers should therefore be aligned as follows:
(where you point)   (target retrograde)   (antitarget)
       -v-                 O         Y

As you thrust, the target retrograde icon will be pushed away from where you're pointing and over the anti-target marker. Looking at the map, this should increase your time to intercept and bring intercept distance down to zero.

For the next bit, a quick bit of arithmetic is always useful. You should have a rough idea of acceleration from the last manouvre node you burned (unless you have KER or MechJeb to tell you exactly what it is). Let's say it's about 8 m/s². Now look at your relative speed to target and divide. So if it's 100 m/s then that makes 12.5 s that you need to get down to zero.
Therefore, if you have got the chevron down to 0.0 km, you need to wait until time to intercept is about 10-12 seconds and then burn hard retrograde. Or you take it a little easier, start at 30s out and burn retrograde until you're down to 20 m/s difference or so. You might need to "push the marble" again to get retrograde over anti-target. Wait a few seconds (since you've slowed, the orange chevrons will have moved along the orbit some more) then when you're about 10 seconds away (10 x 20 m/s = 200m), burn retrograde again until you're down to 5 m/s. Now switch to outside view. You should see that you're about 100m away and heading directly to target at 5 m/s. Burn retrograde gently until it's down to 1 m/s or less, turn the ship around to face the target and use RCS and keys IJKL-HN to do your final approach.

If you do all that right, you will have matched orbits with the target as efficiently as possible, in the minimum amount of time and the minimum fuss.

You can find some examples (for an older version of KSP) here: https://imgur.com/a/vGrJx

There is also a bit of "pushing the marble" in this orbital rescue album, but without ever actually getting the retrograde marker over the anti-target: https://imgur.com/a/c1QJR

1 hour ago, hhatch said:

I'm going to put plan B into operation. I'm replacing mono propellant with beer.

Less monoprop wasted = more space for beer.

[Ty Tan Tu]

Another tip that might help you is limiting your engine's thrust. If you right click on your engine you can limit the trust. It will give you finer control in adjusting your inclination. With practice you should be able to get it to NaN, which I think stand for "Not a Number" meaning dead on zero.

As Plusck says, don't worry about the node for inclination. If you right click on the AN/DN chevron the numbers will stay visible. Wait until you are almost right on top of the AN/DN chevron to fire normal/anti-normal. 

Docking was the hardest thing I had to master in KSP. When I finally did it the first time, it freaked me out. BOTH ships raced away from me. I was like "NOW what did I do wrong." Then I realized "Oh, they are docked." 

When you get there, savor the moment. Then separate the two ships, let them drift a bit apart, and dock again using RCS. Pretty soon you will be launching ships off of Minmus' surface straight up to your space station without having to orbit at all.

Edited December 20, 2017 by Ty Tan Tu

[hhatch]

3 hours ago, Plusck said:

You can use either set, whichever is closest. However, the real answer is probably more like "neither"... because if you do the right job of "pushing the marble" as you approach the first orange set, you'll end up with the intercept point being somewhere between the two. I'll explain a bit further down the page...

And this shouldn't make any difference to the difficulty of docking.

The main "trick" is just to do about 95% of your burn at normal thrust, then delete the node and finish up the burn while watching the map view at minimum thrust. You should see the chevrons get closer and AN/DN drop to zero.

The next trick is to fine-tune using RCS keys IJKL-HN. When finishing the burn, as soon as the chevrons and/or AN/DN start getting further from what you want, stop immediately. Turn on RCS and use "N" to reverse thrust. Then try each of the directions IJKL in turn to see which one(s) you need to bring the chevrons and AN/DN down to where you want them.

This is where you really have to learn to "push the marble". And keep your eyes on map view all the time. RIght-click on your target and on the orange chevron so that they both show up and you can see (a) distance to target, (b) time to intercept, and (c) distance to target at intercept.

Then don't do anything until you're a minute or so out (unless relative velocities are in the hundreds of m/s, then start earlier).

At one minute from intercept or so, turn to target retrograde, look to see where the anti-target (pink upside-down Y) is, and thrust on the other side from prograde. On the NavBall, your markers should therefore be aligned as follows:
(where you point)   (target retrograde)   (antitarget)
       -v-                 O         Y

As you thrust, the target retrograde icon will be pushed away from where you're pointing and over the anti-target marker. Looking at the map, this should increase your time to intercept and bring intercept distance down to zero.

For the next bit, a quick bit of arithmetic is always useful. You should have a rough idea of acceleration from the last manouvre node you burned (unless you have KER or MechJeb to tell you exactly what it is). Let's say it's about 8 m/s². Now look at your relative speed to target and divide. So if it's 100 m/s then that makes 12.5 s that you need to get down to zero.
Therefore, if you have got the chevron down to 0.0 km, you need to wait until time to intercept is about 10-12 seconds and then burn hard retrograde. Or you take it a little easier, start at 30s out and burn retrograde until you're down to 20 m/s difference or so. You might need to "push the marble" again to get retrograde over anti-target. Wait a few seconds (since you've slowed, the orange chevrons will have moved along the orbit some more) then when you're about 10 seconds away (10 x 20 m/s = 200m), burn retrograde again until you're down to 5 m/s. Now switch to outside view. You should see that you're about 100m away and heading directly to target at 5 m/s. Burn retrograde gently until it's down to 1 m/s or less, turn the ship around to face the target and use RCS and keys IJKL-HN to do your final approach.

If you do all that right, you will have matched orbits with the target as efficiently as possible, in the minimum amount of time and the minimum fuss.

You can find some examples (for an older version of KSP) here: https://imgur.com/a/vGrJx

There is also a bit of "pushing the marble" in this orbital rescue album, but without ever actually getting the retrograde marker over the anti-target: https://imgur.com/a/c1QJR

Less monoprop wasted = more space for beer.

Thanks for all the info. I just tried again using some of the techniques you suggested. I was within 3 m of docking but could not make it. I'm just not comfortable with RCS controls yet. Can RCS be used in conjunction with SAS ? I'm assuming when real close I would not use SAS. My problem seems to be that I'm disoriented. I don't know what's up, down. left , right and so on.

[Ty Tan Tu]

NavyFish has a Docking Port Alignment Indicator mod that can help. It is not an auto docker, but gives you a good display to help you move in the right direction when get that close.

https://spacedock.info/mod/543/Docking Port Alignment Indicator

[James Kerman]

7 minutes ago, hhatch said:

I don't know what's up, down. left , right and so on.

If you're getting to 3m from docking you're nearly there, mate.  I use SAS to hold target or anti target, depending where the port is and the I use RCS to keep prograde lined up with the target.

I only use the navball information when docking.  The only thing I worry about is that my prograde and target marker are lined up (trial and error with little pulses using (I K J L) and speed relative to target (to set your speed information to target click on the speed box on top of the navball until it says target).

When you are close (100 - 50m) cancel your relative speed (either H or N, depending on if you are holding target or anti target) while adjusting (I K J L) to keep the prograde and target markers lined up.  Just before you push in to dock, switch to your target vessel, right click on the docking port you wish to dock and select control from here.  Then target your original vessel and select the target SAS option.  Now switch back to the docking vessel - your ports should be lined up and orientated.  Push a little (H or N) to close the distance, I usually do this at 1 or 2m/s and slow to 0.2m/s to actually  dock.

 

[hhatch]

Look what I found.

 

[FrostedShoe]

11 hours ago, hhatch said:

 My problem seems to be that I'm disoriented. I don't know what's up, down. left , right and so on.

Put the camera in chase mode

[Zhetaan]

This video is old enough to be an archaeological study, but it is still the best docking tutorial out there.  That's because when this was made, there simply weren't any good docking aids in KSP yet (not only was there no prograde/retrograde hold, there weren't any normal/antinormal navball markers, either), so if you wanted to dock, you had to do it with a minimum of help.  What this means for the current player is that if you can learn to dock this way, then it will never trouble you again.

 

[hhatch]

1 hour ago, Zhetaan said:

This video is old enough to be an archaeological study, but it is still the best docking tutorial out there.  That's because when this was made, there simply weren't any good docking aids in KSP yet (not only was there no prograde/retrograde hold, there weren't any normal/antinormal navball markers, either), so if you wanted to dock, you had to do it with a minimum of help.  What this means for the current player is that if you can learn to dock this way, then it will never trouble you again.

 

I looked at this video and it looked a lot like some other older videos I have seen. I was not even aware until very recently there were aids you mentioned above so I was trying to dock basically using the procedure outlined in the video. It became much easier once I started using those aids. However, I went back and used the chase camera view and tried maneuvering again without aids. One of the things I did not do was when I wanted to go in one direction I did not do enough of a counter thrust to stop the motion. Moving in a vacuum is a lot different than my flight simulators. Looking at the direction of the thrusts helped me stay oriented. I think with some practice I might be able to do it.

Thanks to all for the help. I think there is a need for updated videos although the basics of the old ones are still valid.

[Corona688]

1 hour ago, hhatch said:

Moving in a vacuum is a lot different than my flight simulators.

One of our standard questions ought to be "have you used other flight simulators", I think.  It never occurred to me to wonder if you were fighting old habits.  Or else we might explain how that works, rather than just "how to move the correct direction".

Edited December 20, 2017 by Corona688

[Plusck]

13 hours ago, hhatch said:

Look what I found.

Hah, congratulations.

I've often wanted to do an updated docking tutorial but I've never managed to get good video capture.

Personally, I always use "locked" view on the camera for the last few metres, and "SAS hold" on. I don't like target hold because any deviation from lateral alignment will automatically cause you to move out of rotational alignment. And in "locked" view only up and down are reversed, just like on a standard flight sim, so it's easy to eyeball.

But above all, it's the NavBall you need to watch. Once the two ships are aligned (even if it's 200 metres away), give warp a short blip to stop them moving, then just concentrate on keeping the prograde marker over target with IJKL-HN. if you don't rotate, you'll still be perfectly rotationally aligned with the target... you might have to move sideways to compensate but that's just the other part of "pushing the marble": moving the prograde icon around to push the target marker towards you.

 

It's not very easy to get your head around the NavBall, but its information is priceless. For some people it helps if they imagine standing in a room, with the navball marking painted onto the walls.

So if the target is above and ahead of where you're pointing, then you need to head upwards at a slightly sharper angle. As you do so, the target icon will drop until you're pointing straight at it: therefore you use RCS to push prograde up, and that makes the target icon drop.
If, on the other hand, you thrust forwards, the prograde icon will drop down below the target, and as you approach the target will sail over your head: prograde is "pushing" the target icon away.

[hhatch]

2 hours ago, Corona688 said:

One of our standard questions ought to be "have you used other flight simulators", I think.  It never occurred to me to wonder if you were fighting old habits.  Or else we might explain how that works, rather than just "how to move the correct direction".

I do think experience with flight simulators did help me.Like docking, landing a plane requires continuous small adjustments and a light hand on the controls. It helped  a bit with the navball but the environments are quite different.

[foamyesque]

The tricks with docking's final approach are these:

 

1. Point your docking ports normal and anti-normal to your orbit (on an equatorial orbit, that means North/South), using the 'control from' to make sure you're aligning the docking ports and not the ship. That means that your docking adjustments should have the least possible impact on your orbits, since you're effectively trying to do a plane change, and it also means that they will never change direction relative to the horizon of your navball, which makes it much easier to align them.

2. Once you've set the alignments, ignore everything except the navball. The main view is a distraction; the navball is everything. Your job is to get three markers to line up: The center of the navball, the pink target marker, and the green prograde marker. The trick here is to 'herd' the target marker with your prograde marker; the target marker will always try to slip away from the prograde marker (unless they're precisely lined up), so what you want to do is chase the target marker into the center of the navball by putting the prograde marker on the same line, but further out from the center. This will guarantee that you will be lined up and oriented to your target port before you get there, though you might be floating only 10m from the thing. Once the target marker's centered, just put the prograde marker inside of it and gently thrust forward. At this point, if rotational relative to the docking port is important (usually isn't, but can be), you can then pay some attention to the main view in chase mode to fix that.

 

 

[Ty Tan Tu]

20 hours ago, hhatch said:

Look what I found.

 

That most be some kind of a bug. I am sure it will get fixed in the next version. :-)

You never mentioned you were using the Clamp-O-Tron Jr. I am sure that made it a bit harder for you on your first attempt at docking.

Anyways, Cheers!