Trying to build a space station

[oanto80]

So with th new workshop features some cool crafts have been shown just like this space station made by Llandon : https://steamcommunity.com/sharedfiles/filedetails/?id=1418085963

My idea was to try to bring it into orbit piece by piece but whenever I tried I was not able to do it. Im not new to the game but I havent played a lot recently and I havent been able to figure out how to build a rocket to firstly launch the left part on this picture

 

All the rockets i haved trIed weren't stable and i'm not sure why here is some pictures of what i have made : 

 

 

I have added an antena at the other side of the rocket to prevent it to flip over and over but it havent helped at all and the rocket wont go strait. I have tried to take of the assimetrics parts and add some "blanket" on the top but same problem...  the total weight of the payload is 18 tones

 

It will be awsome if you could help me to find out a rocket design

thanks a lot

 

ps: I'm not a nattive speaker sorry fo all the errors

Edited June 28, 2018 by oanto80
imgur newbie

[Vanamonde]

Welcome to the forum, oanto80.

Unfortunately, Imgur updates keep breaking album posting to this forum. How about linking the individual pictures? 

[oanto80]

Yep it seems all good now thank you 

[Aeroboi]

Use Search function 1.0: Most of these questions about rocket stability and cargo delivery are common questions with often near identical answers that can be found in multitude using the search function.
Anyway, I do want to address it. My advice may be quite in depth but there's so much to say for this when I see that picture, here goes.

Stuts and joints 1.1: Docking port connections are unstable. Better attach a decoupler to a docking port for more rigidity. I'm referring to the docking port connection of the center Kerbodyne S 14400 tank to the cargo there above. When doing this you may not need these struts sticking out. I myself use autostruts when in need for sstructural integrity. I find them more rigid then the strut parts. You have to enable advanced tweakables in the main main menu general settings to use autostruts. Then right click and use "autostrut" to enable it on a part in the editor. 
If you grandparent autostrut the docking port to the stage that pushes it and the parts above that to the heaviest parts you should solve most of the wobbling, which I suspect you experience.

Lift, and drag 1.2: A secondary part of stability especially when going through the atmosphere is the Center of Lift (CoL) The Center of Lift is visualized in blue by clicking the right most icon in the vab/sph next to CoM (yellow) and CoT (purple) 
In almost all cases you want this blue marker to sit below the yellow com marker. You haven't activated CoL and it should be seen in your picture if you want to receive the best advice.

A third part of stability is drag. A engine creates more drag then a nosecone since it isn't pointy. You have the LV-N Nerva atomic rocket motor on top of your rocket that catches a lot of air more so when going faster. That forces the rocket to pivot due to drag. Even if you have a lot of weight near the bottom of your rocket to counter act that drag you can expect a lot of wobbling on the ascent.

If you had to go with this design you want to use the fairing to shield parts from unwanted aerodynamic forces, protect parts and to make the rocket go faster. In a nutshell: Using a fairing is a triple win.
You can press F12 in flight for aerodynamics overlay. This will visualize the forces on your rocket that cause instability. Pay specific attention to red stripes which are drag indicators when your rocket gets up to speed with the overlay activated. 
These drag indicators should especially be visible once the rocket wobbles, wants to pitch or yaw on its own or have any other stability issues during the ascent.

I see you have fins on the center stage but aren't they small in comparison to the whole rocket? I would just use large wing pieces there myself, ones without control authority which you don't need as you have gimbal on those engines. 
Remember that drag isn't visualized by CoL and hasn't got a indicator in the editor. What you want is to have the lift indicator in the VAB well below the CoM. And by 'well' I really mean as far down as you can get it because the lift has to counteract the drag at the top. In stock KSP you can only guesstimate how far down you want the fins to be but if you want to use a mod to calculate this you could use Correct COL.

This let's you visualize stability in the editor while taking aspects of lift, drag and Center of weight into account.

Wett/Dry Mass 1.3: A rocket at launch has a lot of fuel (Wett mass) As it burns fuel it looses this weight and only the weight of the structure (tanks, cargo etc) remain (Dry mass). The center of mass is usually not similar between Dry/Wett states unless you particularly optimize your rocket for it. In your case this difference is likely a great contributor to instability. The LV-N nerva rocket motor weights a lot. Unfortunately it is all they way at the top of your rocket. When you have unstable aerodynamics the dry weight of a engine near the top that catches drag will create a strong pivoting force causing the top of the rocket to flip. As you burn more fuel, the center of mass will shift further and further to the top. For stability reason you want your dry mass to stay as low as possible. In your case I would rotate the cargo stage by having the Nerva near the bottom conneted to the 1st stages with a decoupler in between and put a fairing over the entire section of cargo to reduce drag.

[Atkara]

59 minutes ago, Aeroboi said:

If you had to go with this design you want to use the fairing to shield parts from unwanted aerodynamic forces, protect parts and to make the rocket go faster. In a nutshell: Using a fairing is a triple win.

This.

[Kesa]

Welcome aboard!

Some general things you should be automatically thinking of when failing to launch an unstable playload :

1. Where is the fairing? Where is it?
2. Use ailerons. They are barely visible. If the craft is not stable, use bigger ailerons
3. Use engines with vectoring abilities. Skipper has a decent gimballing for stable rockets, but for unstable rocket, you probably want to complement it with thud or vector engines.
4. Check the torque. It's good that you checked it, but thrust offset is usually the smallest issue. I see you still got some thrust offset in the tens of Nm but I think it should be well within skipper gimballing capacity.

 

Some advanced tips to launch stuff into space

1. Empty the fuel tanks of your playload. You got way too much Dv, 4,000 m/s should be more than enough to go to LKO. You can half the weight of your playload by just emptying the three LF tanks and the big monoprop one. You don't seem to even use the Nerva as our upper stage, which would increase the playload mass but reduce the overall weight of the craft. Think BFR. Refueling the empty playload/the station with an aerodynamic tankers should be a trivial task, especially compared to launching a heavy unstable playload.
2. If all else fails you can launch a very unstable playload between two rocket rather than on top of one.

 

TL;DR use fairing, empty fuel tanks which do not contribute to orbit.

Edited June 28, 2018 by Kesa

[Vanamonde]

And now that we can see what sort of question you're asking, the thread has been moved to Gameplay Questions. 

[oanto80]

Alright thanks to your good advices I figured to send into orbit and dock two parts as you can see bellow but I still have some issues  firstly I have a strange bug that makes the earth always dark in the close view even if the sun is just infront of it it ( as we can see in the map view) it feels like if my station were a geostationary satellite always in dark which is not. the second issue is that I never get electrical power with my panles maybe it is linked ? have you ever eared of this strange bugs ? I haven't found anything like this on the web.

 

 

Thanks again for your help !

[FireKerb]

Probably an issue with scatterer. Try removing it.