Dealing with very large ships

[king of nowhere]

I have a ship with 900 parts, and i'm afraid that count is going to become higher before it can become smaller. No, don't ask, I need ALL of them, and I already tried to keep the numbers down. I am using kerbalism, so I need to include extra redundancies in case something breaks. I really do need this huge thing. And I spent a couple weeks planning the mission, I'm not keen on giving it up.

As you all know, ships with too many parts, especially when connected by docking ports, are prone to breaking. at some point some parts will start shaking, and the shaking will propagate to everything and get worse, until you lose some parts of the ship. turning SAS off helps, but only mildly. I'm not sure if autostrutting makes things better or worse, but it has some problems with kerbalism, so i'm  trying to use it as little as possible.

Any advice on how to handle ships with huge part count without them disassembling spontaneously?

thanks

[king of nowhere]

I have discovered that when it starts shaking, i can quickly speed up time to stop it. the loss of rotation upon speeding time is considered a bug, or an engine limitation at best, but in this case it's saving me. anything else?

[bewing]

Use grandparent autostruts across each docking port boundary and decoupler boundary, and a maximum of five root part autostruts -- one from each section of the craft. If it has more than five sections, start at the very back section and work forward.

Are you trying to launch this from the ground, or is it already in orbit?

 

[king of nowhere]

also, my behemot is making the game lagging hugely. which is absolutely expected, but not also when i'm not controlling it. i am in the space center, going from the tracking station to the vab, and still it lags hugely. why is that?

[Guest]

Autostrut to grandparent part all through the main structural parts of the vessel, and autostrut to root part from the extremities. Put your root part near the middle of the craft for maximal rigidity.

Note that if you dock and undock a lot, the root part will change, which may summon the Kraken in case you’re using autostrut to root wrong or too much. 

To reduce wobble under thrust, reduce the gimbal limit on your engines. Especially high-thrust, high-gimbal engines like the Vector can cause disasters.

[king of nowhere]

Just now, bewing said:

Use grandparent autostruts across each docking port boundary and decoupler boundary, and a maximum of five root part autostruts -- one from each section of the craft. If it has more than five sections, start at the very back section and work forward.

Are you trying to launch this from the ground, or is it already in orbit?

 

it's already in orbit. the biggest part i launched from the ground was 550 parts, reduced to 330 after staging. to that i added 4 refueling vehicles, because i will have to do a lot of refueling, and with a chance to blow up an engine at every trip i wanted backups. and 4 crew escape pods. and now I will need a few landers, but i'm mostly done

[AHHans]

As @bewing and @Brikoleur already mentioned: use autostrut to grantparent. I personally don't use autostrut to root often - essentially only on craft where I absolutely need it - because of the issues with docking.

If you craft starts shaking and the shaking gets worse and worse, then this may be because your control point (cockpit etc.) and the "torque generators" (e.g. gimbaled engines or reaction wheels) are at different ends of a "floppy" structure. In this case SAS will increase the flexing of the structure: if the structure is bent in one direction, then the control point points off-axis so to point back on-axis again it needs to turn into one direction. But if you then grab the other end of the structure and rotate it in that direction you actually increase the bending of the structure. Because SAS looks only at the direction of the control point it doesn't know about the flexing of the structure and will actively increase it.
My solutions are to a) switch SAS off and b) have the control point close - or at least rigidly connected to - the "torque generators".

[Spricigo]

My usual advice to how to deal with large ships is: don't.  Yes, it can be done, but at a certain point I feel is just simpler to send multiple crafts.

In any case, for big ship is even more important to avoid weak joints.  Give preference for Sr docking port; don'y use tiny parts  for root if you are expecting to use autostrut-root; if for some reason you need to use smaller part mid-stack, put those inside a cargo/service bay for structural purposes ; be careful with autostrut root/heaviest since those parts may change.

I don't know if  struts can be placed with stock EVA construction, but there is the mod option EVA struts. 

[AHHans]

7 minutes ago, Spricigo said:

I don't know if  struts can be placed with stock EVA construction, but there is the mod option EVA struts. 

Good point! That should be possible in stock now. But I haven't had much time to play in 1.11 yet.

[king of nowhere]

ok, putting some autostruts stabilized the structure against shaking. I hope it won't mess too badly with kerbalism. I felt safe in autostrutting to heavier, because

1) I have 4 S4-512 tanks on the main body that are, without competition, the biggest parts. no risk of priority being swapped

2) the heaviest parts were often quite far from the center. as in, the mining vehicles are attached through a docking port, and attached to that is an RGU, 2 food containers, one adapter, a crew pod, a crew living space, a convert-o-tron, and finally a big S3 tank. If I root the S3 tank to grandparent, I fear it may get strutted to a crew pod, or food container, with no gain; i need it strutted to the main body.

Even then, I quickly speed up the game every time i finish manuevering, just to ensure there is no remaining structural stress.

For now it's holding. i never had problems with shaking again. And I am almost done. I only need to attach 2 more pieces, a rather small one with 40 parts, and the big eve lander, that's a 200 parts behemot. On the plus side, Eve is my first stop, so I will drop that pretty fast.

It still lags horribly, but there's not much to be done for it. It's less bad if I restart the pc regularly.

Yes, the smart thing would be to not launch a ship so big. but as soon as i installed kerbalism, I wanted to see if I could run a grand tour mission, dealing with life support, radiations, and malfunctions all along the way. planning and anticipation have been obsessing me for the last couple of weeks, and I will see my dream to the end, successful or not.

 

thanks everyone. any further advice would still be welcome

Edited December 24, 2020 by king of nowhere

[AHHans]

41 minutes ago, king of nowhere said:

Even then, I quickly speed up the game every time i finish manuevering, just to ensure there is no remaining structural stress.

Time-warp doesn't eliminate structural stress / deformation, it only eliminates relative motion. So it does help against the shaking, but not in the way you wrote down. (But probably they way you meant.) But you really shouldn't need^(TM) to do that, just switching off SAS and giving the structure time to relax should be enough. But for something really wobbly (e.g. my Very Kerbal Array after unfolding) I switch time-warp on and off a number of times to speed up the process.

47 minutes ago, king of nowhere said:

It still lags horribly, but there's not much to be done for it.

Not really. The only thing that really helps is getting a faster computer. (Faster single core speed, not just more cores of the same speed.) But if rebooting the PCs really helps, then it might be that you run out of memory, so getting more of that might help. (If you already have 16GB or more, that probably not!)

[Zhetaan]

2 hours ago, king of nowhere said:

any further advice would still be welcome

I have some:  post pictures.

[king of nowhere]

2 minutes ago, Zhetaan said:

I have some:  post pictures.

I will open a detailed mission report for it as soon as i have the whole thing assembled. Several people told me it's impossible to make a grand tour with kerbalism, and I intend to settle the matter one way or another. But first I want to have the whole ship assembled, because I wasn't sure the game would even be playable at all with it. Now I am quite optimistic. As long as I can deal with the roughly 5 frames per second, and the couple minutes load whenever the main ship comes into physical radius.

I like my monstruosity enough to deal with that. the only thing I regret is not being able to put a gigantic  "DREAM BIG" logo on it.

[king of nowhere]

6 hours ago, Zhetaan said:

I have some:  post pictures.

well, the report will be long and wordy and will wait tomorrow, but I can share some pics

This is Home in all its illogic glory

In more detail, the fuel tanks and shuttles

greenhouses and various amenities

the eve lander

A perspective to fully appreciate the number and variety of service ships

but i didn't really realize how goddamn BIG this thing is until I came to this last perspective: an EVA kerbonaut went to repair the engines, and upon coming back, it was faced by a wall of spaceship

1191 parts. 3662 tons when full

 

For a moment it was even bigger, I sent a special fuel tank to replenish it, to start the voyage with full tanks.

it's 400 tons of tanks, but it's dwarfed by the colossal ship

 

[SpaceFoon]

Just use Kerbal Joint Reinforcement. Also use Tweak Scale, UbioZur Welding and Procedural Parts when you can to cut down on part count.

Edited December 28, 2020 by SpaceFoon

[Incarnation of Chaos]

2 hours ago, SpaceFoon said:

Just use Kerbal Joint Reinforcement. Also use Tweak Scale, UbioZur Welding and Procedural Parts when you can to cut down on part count.

Yep, and consider getting mods for parts > 3.5M also. After a certain point having a stack of 20 parts at 5 or 10M is much, much better than 300+ at 3.5M