Kraken-resistant stations

[Guest]

In my ongoing career, I've had a number of brushes with the Kraken when dealing with space stations. There are three scenarios in play:

1. Docking. The Kraken strikes immediately after docking. The giant invisible tentacles wrap around it and shake shake shake until it falls apart.
2. Undocking. As above, but on undock, and only one craft is directly affected (although the other might get damaged by flying pieces of rocket).
3. Fuel transfers. This starts with a tiny insidious little vibration as fuel is transferred from one craft to another. Sometimes it stops if I quickly stop the transfer, at other times not. If I'm connected with the Klaw, setting Free Pivot may or may not help.

Some hypotheses I've come up with:

Scenario 1 happened with a long skinny station when I docked another long, skinny, but heavy craft to a port near its centre. Even though the docking event was at a low speed (0.6 m/s or so), the bump appears to have induced an oscillation along the length of the station, which then amplified into a full-scale Kraken attack. Possible solutions: don't make long skinny stations? If you do, don't dock heavy craft near their centrepoint?

Scenario 2 happened repeatedly when undocking a heavy spaceplane from a station, or when undocking a cargo module from a heavy spaceplane. I believe I traced this down to excessive use of Autostrut to Heaviest Part. When I undocked, the heaviest part was removed, the autostrut reconfigured itself, and the rapid changes summoned the Kraken. Possible solution: don't use Autostrut to heaviest part, or only use it sparingly?

Scenario 3 happened repeatedly in scenarios where I had a heavy craft docked to the station orthogonally and was transferring fuel between the two, which shifted the CoM laterally. I'm not quite sure what the contributing factors to this are, except that Autostrut to Heaviest Part certainly makes it more likely.

What techniques are you aware of that would make stations less prone to summoning the Kraken, apart from being very careful when using Autostrut to Heaviest Part? Which geometries are more Kraken-resistant? How do you configure a station that has lots of docking ports to accept different kinds of incoming craft, but doesn't summon the Cosmic Dread Lord when large craft dock with it?

[drhay53]

I guess I have two thoughta really. 

1) the mod kerbal joint reinforcement should help with the wobbly death spiral

2) likewise, minimize the use of reaction wheels on the station. In my experience attitude stabilization is a common source of the wobbly death spiral kraken. 

[Guest]

That's a good observation. So switching off SAS just prior to docking, undocking, or doing fuel transfer would help?

[monstah]

Another thing, always have a probe/command pod/docking port near the station's CoM you where can "control from here". Having the station's control point be near an extremity makes it feel a lot more vibrations, and compensate in incorrect ways throughout the station.

[MaxwellsDemon]

I tend to use Construction "docking ports" to weld modules together if I'm not planning to swap them out or move them-- that cuts down on some of the flex in the structure.

If I see the wobbling start, I shift to another vessel out of physics range and then back again-- seems to settle things down.  (This works for "dancing" landers, too, though sometimes KSP will object to switching "while moving over the surface.")

And, then there's good old KAS EVA-applied strutting.  Give those engineers something to do!

Edited March 1, 2018 by MaxwellsDemon

[LordFerret]

I've stated this many times before, turn the station's SAS off. The station doesn't need SAS.

I use docking cameras when I dock. Can't live without'em. As I near the docking collar, close, real close, velocity is cut to 0.1m/s... when the docking port's magnetics kick in, the collar gets bright (lights up)... at that point, I kill RCS and SAS. The ship just snaps into place. With everything already off, I don't have to worry about changing/messing with SAS/RCS states on the station itself. I also keep a chart of what action keys are in use by which craft that are docked, because not thinking and attempting an action (like opening/closing cargo bay doors while docked) could have unwanted consequences elsewhere on the station. I myself do not find 'long' stations an issue.

Ice Station Zebra (300km orbit)...

[drhay53]

2 hours ago, Brikoleur said:

That's a good observation. So switching off SAS just prior to docking, undocking, or doing fuel transfer would help?

As others have said, it's best to just have SAS off entirely. On fuel transfer, you're redistributing the mass, so it's really kind of the same as docking in some sense. These are all symptoms of the same problem, which is that the attitude control systems are causing wobbling (my guess is that it's likely because it takes some time for the torque to actually transfer through the craft). When you're about to dock, you want to have all sources of potential attitude control off as well. 

 

[MaxwellsDemon]

I have gotten into the habit of shutting off SAS and RCS once the docking ports have clearly "locked on" to each other-- I noticed that otherwise there can be some mutual "shimmying" that was (1) annoying, (2) wasteful of monoprop and time, and (3) reminded me too much of Soyuz 10.   Looks like there's an additional benefit to it (noted above)...

[Atkara]

As you deduced, your troubles with undocking are most propably a result of autostrutting to the heaviest part. Also, if your fuel transfer is enough to make another part as the heaviest, autostrut will comply. Not sure what happens afterwards, as I always autostrut to the grandparent part, to avoid possible complications. Has worked well so far, no matter the extent of it.

As for the 1st problem you described, leaving SAS on after docking can have a similar effect -but I'm not sure if this is the case with your station.

Edited March 1, 2018 by Atkara

[Mike Mars]

I too have learned to disable reaction wheels after docking.  This practice has eliminated the wobbles.

I have noticed lately though, that when I undock from a station, the craft which has undocked does a shake and a shimey.  I don't activate reaction wheels until after I undock so I am not sure what is causing this problem.

MM

[LordFerret]

11 hours ago, Mike Mars said:

I too have learned to disable reaction wheels after docking.  This practice has eliminated the wobbles.

I have noticed lately though, that when I undock from a station, the craft which has undocked does a shake and a shimey.  I don't activate reaction wheels until after I undock so I am not sure what is causing this problem.

MM

I don't know for sure, but if I had to guess (and I am), the shake could be related to physics kicking in (taking over) the undocked ship having now become a separate entity of its own.

[Mike Mars]

2 hours ago, LordFerret said:

I don't know for sure, but if I had to guess (and I am), the shake could be related to physics kicking in (taking over) the undocked ship having now become a separate entity of its own.

That could be, but why doesn't it happen all the time?

I have different kinds of craft docked to my station; probes, spaceplanes, landers and pods.  There is no pattern I can detect.  Most of the time there is a clean, smooth undock.  Other times the undocking craft dances like Chubby Checker. One poster mentioned struts might have something to do with the problem, but I never use struts.

I always follow the same undocking procedure.  All reaction wheels and MechJeb are turned off until the craft has safely undocked.

More of a nuisance than a problem so far.  Just wish I knew why.

MM

[LordFerret]

10 hours ago, Mike Mars said:

That could be, but why doesn't it happen all the time?

I have different kinds of craft docked to my station; probes, spaceplanes, landers and pods.  There is no pattern I can detect.  Most of the time there is a clean, smooth undock.  Other times the undocking craft dances like Chubby Checker. One poster mentioned struts might have something to do with the problem, but I never use struts.

I always follow the same undocking procedure.  All reaction wheels and MechJeb are turned off until the craft has safely undocked.

More of a nuisance than a problem so far.  Just wish I knew why.

MM

Well, speaking of nuisances, at least you get to see your ship undock... for some reason, when I undock a ship, the view always snaps around to 'elsewhere' (as in anywhere else other than where I was viewing from at the time), and I have to rotate around back to place.

[radonek]

On 1. 3. 2018 at 2:49 PM, monstah said:

Another thing, always have a probe/command pod/docking port near the station's CoM you where can "control from here". Having the station's control point be near an extremity makes it feel a lot more vibrations, and compensate in incorrect ways throughout the station.

True, but in my experience position of the controlling part is also a factor. Radially attached parts can induce feedback loop that is much more dangerous then wobble from far-off control.

On 1. 3. 2018 at 4:21 PM, MaxwellsDemon said:

And, then there's good old KAS EVA-applied strutting.  Give those engineers something to do!

Struts can also make things worse. I learned the hard way to not attach any struts to klaw, landing legs or wheels. There may be other sensitive parts, I'd certainly be careful around anything with moving pieces.

My personal antikraken checklist is along these lines:

1. Turn of SAS. If Kraken continues to attack, ship is doomed. Switching vessels may help now, but Kraken is part of ships desing and will wake up again sooner or later.
2. Turn off all reaction wheels.
3. Pick a "major axis", enable reaction wheels directly at this axis. Avoid radialy attached parts.
4. Set control to part in this axis, preferably close to CoM. Again, avoid radial.
5. Turn on SAS. Kraken should remain calm.
6. Enable other reaction wheels one by one. If Kraken wakes up, turn off SAS before disabling offending reaction wheel again. (This is all kinda optional, as space stations should not need much of control authority, but I like to keep things close to operational status if possible.)
7. Quicksave, play around a little and look for design lessons to be learned. So far I've found that  there is such a thing as having too much control authority, "rigid attachment" helps if used sparringly, autostrutting is no substitution for actual struts, clipped parts may cause trouble if not fixed in place…

[Hotel26]

This is good stuff, especially as I spent the day constructing my old-style fuel dump ("Rolling H") for a video.  I'd found some magic combination recently with auto-strutting to reduce the Kraken, but not this day...

I actually suspect things like just bringing in one too many ships close by slows Physics down enough that its invisible fingers start to shake their grip.  I've learned to turn SAS off but it only goes so far.

Long story short, I followed some advice and built something that has no internal docking.  All one piece and flagrant use of clipping but brilliant fuel capacity.  It's the single heaviest item I've ever lifted even when its empty.

Computer physics is great but it doesn't scale up well as a calculation.

Not mentioned above: when the Kraken starts, hit warp factor 2 and back to freeze everything.  It may buy you enough time to rectify/rescue the situation.

[Nazalassa]

Or you could just "dock" by getting your vessel very close to the station, then going in EVA and putting a strut connector between the ship and the station. This could work, or not. I'll try it next time I'll play KSP.

EVA construction mode has a lot of potential!

[Wizard Kerbal]

I’m stealing the solutions from this, and you never realize how wobbly a shuttle is until you try to dock at a small station

[jimmymcgoochie]

4 hours ago, Nazalassa said:

Or you could just "dock" by getting your vessel very close to the station, then going in EVA and putting a strut connector between the ship and the station. This could work, or not. I'll try it next time I'll play KSP.

EVA construction mode has a lot of potential!

This won’t work, you can’t put struts between different vessels, only between parts of the same one. You’d have to be docked first to add struts and undocking breaks the struts automatically.

[Nazalassa]

3 minutes ago, jimmymcgoochie said:

This won’t work, you can’t put struts between different vessels, only between parts of the same one. You’d have to be docked first to add struts and undocking breaks the struts automatically.

Sadly… So you can't strut kerbals together.

But you said undocking breaks the struts — what about the Advanced Garbage Unit?

I'll try it with all the possible ways to dock or attach two vessels!

[Mahnarch]

21 hours ago, jimmymcgoochie said:

This won’t work, you can’t put struts between different vessels, only between parts of the same one.

Aww, seriously?

I usually build fairly large orbital fuel depots but, I position them when they're smol and embiggen them from there.

I had never thought about strutting my tanks together until recently - when I thought about getting fancy with designs - so, I guess you saved me some time. 

[jimmymcgoochie]

55 minutes ago, Mahnarch said:

Aww, seriously?

I usually build fairly large orbital fuel depots but, I position them when they're smol and embiggen them from there.

I had never thought about strutting my tanks together until recently - when I thought about getting fancy with designs - so, I guess you saved me some time. 

You can strut stuff together once you’ve docked (or grabbed with a Klaw) but not while they’re separate, using EVA construction. KIS/KAS work differently and you can connect different vessels up using that, though stability varies wildly and those mods aren’t (yet?) compatible with the stock inventory system.

[Nazalassa]

Well, I tried it and it definitely don't work.

But I have another idea for Kraken-resistant space station: put them as bases on the ground with a Ground Anchor ! 

Just kidding  , my idea is to put an asteroid where you want your station, then install a plugin that allows you to move anything in EVA construction mode and build your station by attaching parts to the asteroid.

Why not making "Kerbal Komet SPA" ? Would be fun!

     ***

I'll try it.

[modus]

Having done that a couple of times, I can say that asteroid stations are more Kraken-inviting than resistant

[Mahnarch]

On 12/15/2021 at 12:21 PM, jimmymcgoochie said:

You can strut stuff together once you’ve docked (or grabbed with a Klaw) but not while they’re separate,~~

Ah! OK. I see what you're saying.

Thank you for clearing that up.

 

Now, to plan my overly ridiculous contraptions!

[Nazalassa]

On 12/16/2021 at 2:09 PM, modus said:

Having done that a couple of times, I can say that asteroid stations are more Kraken-inviting than resistant

Yeah, I'm experiencing bizarre things. I've started a "base" on a class C asteroid and I lost almost 2 hours of hard work in EVA construction mode when I got one of the shuttles back to Kerbin .

In fact, all the base parts placed on the asteroid were placed, say, 50 meters away, and at the same 3D position (screenshots coming).

I've found an old save, when I only placed the cupola from K&K planetary inc. So now I have to rebuild almost everything.

Also, when I said "station", I meant "something that looks like a planetary base, landed on an asteroid".