totm feb 2024 Rendez-vous help?

[Mister Spock]

I used to dock all the time in KSP1, but it's been a while, and I'm struggling here in KSP2. I've matched inclination (after some struggle), and my PE and AP are close to (though not identical to) my target's. I get within 800m of my target, relative speed about 28 m/s. But this is where I get stuck. How do I close the gap? If I point at the target and burn, the relative speed between us increases. I try burning prograde to slow down (if I'm ahead) or retrograde to speed up (if I'm behind), but neither helps. I've watched several videos, and none of them explains precisely which way to burn in this situation, or how to set up my navball. Can anyone advise me?

I did find this video helpful, but he makes it look so easy. He seems to point his ship at the target and use RCS to close the gap and decrease relative speed to zero, but I can't duplicate his feat. 

Also, the UI has changed since that video was made. And maybe not for the better! I often have trouble distinguishing my craft's orbit lines from the target craft's orbit lines -- they're close to the same color. I couldn't figure out whether I was working with an ascending node or a descending one. Likewise, I sometimes have trouble distinguishing between a maneuver node's hypothetical course and my actual course.

Can anyone point me to a remedial rendez-vous course? Once I'm close enough to use RCS to dock, I've got Docking Alignment D. installed, and I'm hopeful I'll be able to handle that. It's the getting to 100m range, 0 m/s relative speed, that's tripping me up. Thanks in advance.

[Bej Kerman]

1 hour ago, Mister Spock said:

I get within 800m of my target, relative speed about 28 m/s. But this is where I get stuck. How do I close the gap? If I point at the target and burn, the relative speed between us increases.

It helps to kill all your speed before pointing at the target (or slightly off to the side so you don't bump into it) and burning. And when you are burning, your relative speed should increase as you move towards the target.

1 hour ago, Mister Spock said:

I try burning prograde to slow down (if I'm ahead) or retrograde to speed up (if I'm behind), but neither helps.

I assume you mean retrograde to slow down and prograde to speed up. Either way, I'm not sure what you mean by "ahead" and "behind". Do you mean in terms of the orbits?

1 hour ago, Mister Spock said:

I've watched several videos, and none of them explains precisely which way to burn in this situation

Where and when to burn is very situational, so there is no "precisely which way". Getting within a few kilometers, killing your velocity and burning at the target generally works.

 

Finally, can you record a video of yourself docking so I know precisely what you're having trouble with? Thanks

[The Aziz]

3 hours ago, Mister Spock said:

. I get within 800m of my target, relative speed about 28 m/s. But this is where I get stuck. How do I close the gap? If I point at the target and burn, the relative speed between us increases. I try burning prograde to slow down (if I'm ahead) or retrograde to speed up (if I'm behind), but neither helps. I've watched several videos, and none of them explains precisely which way to burn in this situation, or how to set up my navball. Can anyone advise me?

I'd finetune the rendezvous so you get within 200m or so first. Just don't get closer than your ship's size, I already caused some explosions like that. Then, as you get close, and that's really depending on your ship TWR, set your navball to target mode (the same way as you switch between orbital/surface), point retrograde  and burn where you think you'll stop the relative movement while close enough, watch the speed, as it is the relative speed so stop firing when it goes close to 0.

From there it's a matter of switching both ships into "point at target" and slowly RCS your way towards the target.

[Dakitess]

I don't understand what could be the problem in KSP2 if you're handling that perfectly in KSP1. Where do you struggle more, what do you find different ?

[gluckez]

just because it's behind you doesn't mean burning retrograde will decrease your relative velocity. It might increase if you target behind you is already going faster than you. like @The Aziz said, change the mode of the navball so it says Target, then burn retrograde relative to the target to match it's speed.

[Bej Kerman]

1 hour ago, Dakitess said:

I don't understand what could be the problem in KSP2 if you're handling that perfectly in KSP1. Where do you struggle more, what do you find different ?

Explained within the first sentence.

"I used to dock all the time in KSP1, but it's been a while, and I'm struggling here in KSP2."

[Kerbart]

2 hours ago, Dakitess said:

I don't understand what could be the problem in KSP2 if you're handling that perfectly in KSP1. Where do you struggle more, what do you find different ?

The navball monumentally blows in this regard. It's very hard to see the target and velocity markers in the first place, or distinguish them.

[steveman0]

My Rendezvous procedure:

1. Use maneuvers to arrange an encounter to within 1 km of target - ideally less than 100 m.
2. Switch navball to Target mode and flip SAS retrograde to target.
3. Time warp/wait until near the planned encounter distance and burn to as close to 0 m/s as possible.
4. Flip SAS control to Target.
5. Burn to a few m/s - usually 1-3 if I'm really close but up to 10 if I'm far away.
6. Flip SAS back to retrograde.
7. Let it spin me around and flip SAS to stability control only.  I perform my final approach braking manually so that I can "push" the retrograde marker onto the target marker with small burns as usually the standard approach alignment will be a bit off.
8. Once I'm basically at my target, finish burning retrograde to stop.
9. Set my target docking port, flip SAS to Target.
10. Switch ships with [ or ], control from target docking port, set nav ball to Target mode, set SAS to Target orientation.
11. Wait for alignment, switch SAS back to stability.  This is important otherwise it can lead to the ship turning and getting you into a weird kind of orbit due to the SAS controls fighting each other.
12. Switch back to my small docking ship with [ or ].
13. Set SAS to stability assist only.
14. Press Delete to enter docking mode.
15. Double check to make sure RCS thrusters have Pitch, Yaw, and Roll disabled.  I find it much easier to do this only with translation and this saves on monopropellant as the SAS tends to eat tons of it.
16. Press R to enable RCS.
17. Press E to begin RCS translation to target.
18. Use W, A, S, D to adjust translation to keep my prograde nav ball marker aligned to target.
19. If you continue to make these fine adjustments and keep approach speed low, you should slowly drift to target.
20. If your angle ended up weird or things shifted due to orbital drift or other effects, you may need to leave docking mode with Delete, disable RCS, and do some angular orientation adjustments to get the docking ports lined up again before returning to docking mode.

[Meecrob]

Click on your velocity display on the navball twice so it displays "target." This screwed me up too, lol.

 

Edited January 12 by Meecrob

[Meecrob]

1 hour ago, Bej Kerman said:

Explained within the first sentence.

"I used to dock all the time in KSP1, but it's been a while, and I'm struggling here in KSP2."

Couldn't be KSP2, it must be the player who could dock in KSP1's fault!

 

[Bej Kerman]

3 minutes ago, Meecrob said:

Couldn't be KSP2, it must be the player who could dock in KSP1's fault!

Are you insinuating the OP is blaming either game?

[Mister Spock]

OP here. Thanks for all those helpful replies. I appreciate that you all took the time to respond.

OK, as a first step, I'll enter target mode and burn retrograde with respect to the target. That's what I was doing wrong -- I was burning prograde with respect to the target. As I mentioned, I haven't docked in KSP1 for a while -- I last played KSP1 a couple years ago. So I'm out of practice, and I'm not blaming either game, and it's mostly user error, lol. I watched videos to get me up to speed, but they contradicted each other and left me confused. Some follow-up comments and questions.

1. Should I be trying to match the target orbit PE and AP? Or is just one of those two enough?

2. If I need to match both, is there an easy way to see the target's PE and AP? My dim recollection is I used to use a mod to help me see that info without switching to the target craft -- maybe KER? For now, in KSP2, either I switch craft to check, or I try to find the AP/PE numbers that don't match my current craft's orbit displays in the lower-left. Those methods work, but they're a bit cumbersome. As I explain below, I have a lot of trouble reading orbit lines and icons.

3. Is there a mod that increases the size and readability of AP/PE AN/DN A1/B1 icons and, especially, the numbers associated with them? They're so tiny.

4. Likewise, is there a mod that changes color or readability of orbit lines? When setting up a maneuver node to change inclination, for example, I have to understand three orbit lines: my current orbit; my target orbit; and the planned post-maneuver orbit. I may have a touch of colorblindness that makes it hard for me to tell which is which. I'm using the Maneuver Node mod, which helps, but it doesn't make orbit lines more readable.

5. @Bej Kerman  My comment about "retrograde to speed up" was not a typo, heh. I was trying to "catch up" to the target (or "slow down" to meet it) by staying in Kerbin-orbit mode and speeding up or slowing down by burning retrograde or prograde, respectively. The theory being that burning prograde produces a larger, slower orbit that slow one down, whereas burning retrograde shrinks the orbit, making one's ship go faster. I used to do my initial rough "catch up to target" maneuvers this way in KSP1 -- if I was behind the target I was chasing, I'd burn retrograde (relative to Kerbin) to get lower altitude, to speed my craft, then circularize and match the target's orbit once I was closer. I recognize this was probably inefficient, lol. I'm now trying to use maneuver nodes to match the orbits.

6. @steveman0 Thanks for that step-by-step summary. Hmm, I'll think about disabling pitch/roll/yaw on my RCS thrusters.  I assume you do this only after you enter Docking mode by hitting delete. (Presumably SAS needs pitch/roll/yaw for its stablization maneuvers.) I would disable them using the parts manager, I assume.

Thanks again to everyone for taking the time to reply. I'll give it another go later today!

Edited January 12 by Mister Spock

[steveman0]

1. For the initial encounter? Doing both will minimize relative velocity, however burning retrograde to target at the encounter will intrinsically match your orbits. Doing it early will simply reduce the burn required to match speed. Because your position won't be identical to the target, there will be some assymetry to your orbit that will manifest as small changes to your relative velocity over time. The closer your initial orbit and distance of the encounter, the smaller this effect will be. If you dock quickly after the encounter, you might not even notice this drift.

2. Once you have a close encounter, you shouldn't need to worry about either crafts' AP/PE. Velocity relative to target will take your focus. Your orbit will change a bit as you move about in your rendezvous, but the time and spatial scale should be irrelevant until docked as long as you don't time warp for a long duration. This drift is why you may need to continually apply corrective translations as you approach your target - especially if you time warp due to a slow approach speed.

6. For small craft that only need RCS for docking, I try to remember to do this in the VAB before it ever launches. Sometimes I forget and rarely I will dock a large craft that needs RCS outside of docking. Checking has become a habit because it is annoying to turn on RCS on a craft that only has stock monopropellant from the capsule only to have the SAS start blasting out much of it while it wobbles around nearly uncontrollably due to the weird stability issues with SAS currently.

 

Edited January 12 by steveman0

[Kerbart]

5 hours ago, Bej Kerman said:

Explained within the first sentence.

"I used to dock all the time in KSP1, but it's been a while, and I'm struggling here in KSP2."

I'm not smart enough to figure it out based on that sentence.  @Mister Spock perhaps clarify:

• You were a docking shaolin in KSP1. Docking would take 3 minutes real world time, spending .1 units of mono prop. But you forgot all of that. What was the trick again?
• Same docking shaolin. You can still do it like that in KSP1 but how on earth do you do it in KSP2?
• After rendez vous you're just trying random things and it's not working
• And so on

Docking is counter intuitive. Yes, move towards the vessel you want to dock with, but if that's from a few km away you don't want to do that too slow. Because different velocity means different orbits and those will eventually result in the exact opposite of what you want to achieve. There's tons of good advice here but it would help if we know with a bit more focus what exactly it is you are struggling with.

[Mister Spock]

25 minutes ago, Kerbart said:

There's tons of good advice here but it would help if we know with a bit more focus what exactly it is you are struggling with.

Thanks for your reply. I think my main issue was remembering what to do once I was about 800m away -- and it turns out I was burning in the wrong direction. I was able to match inclination and (mostly) match orbits up to that point, though I struggled to see the tiny icons and numbers on the orbit screen, as I detailed above. (I really am enjoying KSP2, but many of its fonts are too small for my aging eyes.) Anyway, I'll try again this evening and report back.

Yes, I used to dock all the time in KSP1 (manually, not with any autopilot), but it's been two years since I played, and I'd forgotten what to do once I was within, say, 1 km of the target. And I certainly wasn't a docking shaolin; I docked a lot because I enjoyed making space stations, but I recall a number of spectacular collisions. I remember what I need to do to use RCS for the final docking maneuver, but I'm guessing it won't be pretty! For that matter, it took me a few launches in KSP2 to perform a proper gravity turn, even though I knew perfectly well what I had to do, and I'm still rusty. I did manage to land safely on the Mun on my first try, mirabile dictu.

49 minutes ago, steveman0 said:

burning retrograde to target at the encounter will intrinsically match your orbits.

Ah, I see. That's very helpful.

51 minutes ago, steveman0 said:

Checking has become a habit because it is annoying to turn on RCS on a craft that only has stock monopropellant from the capsule only to have the SAS start blasting out much of it while it wobbles around nearly uncontrollably due to the weird stability issues with SAS currently.

As it happens, both my test craft have monopropellant tanks on board, because I anticipate much wasteful use of RCS as I thrust in the wrong direction, overshoot my target, etc., lol. But I will try your advice anyway, because I need to become more efficient managing my RCS fuel. And everything else in life, really. 

[Scarecrow71]

The very first thing I will say is to use the mods Flight Plan and K2D2.  Flight Plan literally has a function to match the speed of the target vessel, while K2D2 does the burn for you.

Sans that, pretty much everything else that's been said in this thread will help.  Especially the part about changing the navball to say "Target", then clicking anti-target on SAS and doing a burn (as anti-target will make you point away from the target, thereby allowing you to do a burn in the same relative direction as the target, which will decrease your speed relative to the target).

[The Aziz]

Not exactly. It would be if you were heading straight on towards the target (as in: minimum distance on intercept=0), but since it isn't, it's better to point at retrograde as you will cancel all relative velocity even at larger distances.

Picture it with a marble rolling towards a point but slightly off, so it will miss by a small margin, its vector is straight. If you apply stopping force towards the target, it won't cancel the current velocity completely, even worse, it will add some in opposite direction of target. The marble will not only keep rolling but it will be further off than it would be at closest approach.

Locking to target makes sense only in final phase, as in, docking.

[Mister Spock]

OK, so I succeeded in getting a close rendez-vous, following the advice in this thread. It was quite easy once I burned the right direction, lol. My ship is now hovering 50m away from the target.

My trouble now is that my RCS placement seems to be suboptimal. I translate fine along the Z axis (forward and backwards, if you will). But X and Y translation also rotate the ship, regardless of whether I have pitch/yaw/roll enabled. I've used 4 omnidirectional RCS thrusters, no doubt placed too low on the ship's abdomen. I think I was trying to keep the rocket's center of mass low, but I forgot about positioning the RCS at the orbiter's center of mass. Here's a picture:

But I'm wondering if it's not just their placement. When I hit the translate-Z keys, the fore or aft thruster fires alone (one on each thruster block), as expected. But when I hit X or Y translation keys, multiple thrusters on each block fire. Is that how it's supposed to work? Should I be using linear thrusters instead? My issue with linear thrusters has always been: where do you put the Z-translation (fore and aft) thrusters? One would conflict with my engine; the other with my nose's docking port.

Finally, I'm not sure I prefer docking mode to normal flight mode. In KSP1, I think I used the JKL keys. What's the advantage of docking mode? I'm also using the Docking Alignment mod for KSP2, but I don't know if it's any better for me than the navball.

Edited January 13 by Mister Spock
Clarity.

[The Aziz]

The thrusters are a bit wonky now and like to compensate for player input for whatever reason when SAS is on, or sometimes they don't fire in some directions. In general, for long vessels, it's wise to use two sets, one on the top, one on the bottom, in case of short ones, near the CoM so they don't act weirdly trying to self correct while translating. I often just turn off the SAS for those few seconds when I'm translating so I don't end up in undesired position.

And by the time you're there, assuming you can control both ships, you should set them both targeting each other's ports, so you don't have to do too much sideways translation, if you're somewhat aligned and don't move anywhere other than forward/backward.

[Mister Spock]

Thanks for your reply. Maybe I'll try moving the RCS thrusters to the CoM of this little ship, then.

So does anyone ever use linear thrusters? Again, I think they'd be great for X and Y translation, but I'm not sure how I'd set them up for Z translation. Maybe three arranged  radially, pointing down and up out of a ring around the middle of the vessel? I'm half-tempted to try.

[Scarecrow71]

9 hours ago, Mister Spock said:

Thanks for your reply. Maybe I'll try moving the RCS thrusters to the CoM of this little ship, then.

I always place RCS thrusters both above and below CoM, equidistant from it.  Depending on the size of the craft, I may place an additional set of thrusters at CoM as well.  I generally go in x4, but larger ships may require x6 or x8.  YMMV.

[Superfluous J]

This thread makes me miss RCS Build Aid. Can't wait for an equivalent in KSP2.

[Mister Spock]

2 hours ago, Scarecrow71 said:

I generally go in x4, but larger ships may require x6 or x8. 

Just so I understand: you mean one set of 4 multidirectional thrusters around the center of mass? By contrast, if you go with 6 or 8, then you might have 3 or 4 attached radially at the bottom and top of the craft?

If I attach the four-pronged RCS thrusters radially, as you can sorta see I did in my screenshot above, do they work together, or do they fight against each other? I'm worried that they're fighting each other for X and Y translation. That's why I'm thinking of experimenting with linear thrusters.

[Vanamonde]

If they're over the center of mass a set of 4 will not be working against each other. Larger craft might require two sets, in which case yes, 2 sets of 4 works pretty well. 

[HebaruSan]

14 hours ago, Mister Spock said:

So does anyone ever use linear thrusters? Again, I think they'd be great for X and Y translation, but I'm not sure how I'd set them up for Z translation. Maybe three arranged  radially, pointing down and up out of a ring around the middle of the vessel? I'm half-tempted to try.

I tried them with my lander, with mixed results. Here are the fore and aft thrusters (composite screenshots so I could outline-highlight multiple parts):

Spoiler

Those worked fine, but the lateral thrusters placed on the decoupler at the COM never worked, and I was not able to figure out why. Obstructed? Fuel-deprived? A bug? No idea. If anyone has tried a similar design and encountered and solved this issue, please reply.

Spoiler