Spacecraft/Rocket Suddenly pitches over/Explodes (Debris ejected at light speed)

[SaturnianBlue]

Hello,

I've been working on a MESSENGER spacecraft replica for the past few weeks, when I noticed a few days ago that around 12 seconds into the replica of the Delta II launch, bits off the spacecraft are ejected occasionally at light speed and suddenly exploding the rocket also proceeds to pitch over into a death spiral. I can't seem to find a culprit in the logs, but I've been suspecting tweak scale, which most of the spacecraft are made of. The rocket seems mostly unharmed, but in KER displays, the torque jumps from 30 kNm to around 500 kNm, which is fatal even for the rocket, with ~ (slightly tweak scaled) 8 large SAS modules/ 12 RCS/ 4 Vernors. the flight logs and the Console Unity Logs only really say structural failure between wings, which the spacecraft is made of. The photos below show the flight with most of the mods I usually play with, but the result remain practically the same with a barebones ProceduralFairngs, KAC, Module Manger, Tweakscale, Procedural Parts (Which I seem to notice nozzle placement is weird after rollout more than once) Ubio Part welding (some with Twekscale modules installed), and MagicSmokeIndustries, used in hinges.

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Edited April 25, 2015 by SaturnianBlue

[TheXRuler]

First off, welcome to the forums

You say there are wings on your craft and I do see the effect for breaking wings, however I fail to see any wings anywhere.

8 large SAS modules? I would not be surprised if that is what is tearing your rocket apart since stock ASAS can be a bit wonky with oscillations, have you tried using less, or disabling them in the early launch phase? I usually disable all the SAS Modules on a rocket during launch and let the thrusters gimbal do the steering, if that fails I often just stick 3 small rigid fins right at the back as that can work wonders with stability.

Have you read the full list of the do's and dont's of ubiozur welding? I can imagine that would wreak havoc when used on tweaked parts (just speculating).

Though your screenshots help me rule out a few causes, it would help if you could upload some more detailed screenshots, especially of the offset nozzles and the wing parts. If you are using massive (or in some cases even small amounts) of part clipping that could be an issue, if you do it might help to have a screenshot of the affected section. Also, if nothing else helps maybe you could provide us with the craft file, including a list of dependencies, so we can test ourselves.

Also I know this may seem dumb, but have you tried adding MOAR STRUTS or installing Kerbal Joint Reinforcement?

[SaturnianBlue]

Ah, I forgot! I had NEAR, as else the rocket would have flipped anyway (.90 Aero anyway). Yes, I ended up using a massive amount of offset/clipping. I did try KJR a while ago, but I ruled it out because it kept happening anyway. I did follow the guidelines for the Ubio Part welding (as far as I know). It depends on Magicsmokeidustries, Ubios part welding, Procedural Parts (and the blackheart texture additions), Procedural Fairings, and tweak scale. The wings are inside the actual spacecraft, as its main structure (and its thermal shield). Also, the offset nozzles seem to be a visual affect in the VAB...

Edit: Here's the wing parts. http://imgur.com/zc41hQQ

Edited April 25, 2015 by SaturnianBlue

[ghostbuzzer7]

I may have found the answer to your problems. The 3rd stage (The one after you remove the main engine and boosters) is held together by nothing but a decoupler. Add some support struts to it From the top to the bottom. I experienced that trouble a long time ago when I first started. The tip of the rocket wobbles. So start adding some struts (or just use duct tape instead )

-----Edit-----

Yeah based on those images, your rocket's tip is just way unstable

----Edit of another edit-----

Ohh and about your spinning issue, your booster stages are also held by nothing but manifold detachments. As repetitive as this sounds, use struts at the top and bottom of your boosters to prevent them from caving in to your craft and causing the death roll.

Edited April 24, 2015 by ghostbuzzer7

[TheXRuler]

Ohhh yes, struts and moar struts (i think I said this before, didn't specify where though). I always (literally always) put at least 6 struts between the payload and the rest of the rocket. Also the boosters, the radial decouplers are stupidly weak, always strut whatever you strap on the side as the thrust will move the nozzles, inducing weird kinds of torque. This becomes more apparent when you try strappin 3 of the KW-Rocketry THOR II Large (2.5m, longer than the orange tanks) attached with only a decoupler, they just rip off and pile into the rocket Oo et voilá: rapid unplanneddisassembly

[SaturnianBlue]

Well, more struts to the SRB'S and the upper stages helped, but the spacecraft is still ripping itself apart, and when I did get the rest of the rocket to somewhat fly, I met the 6 Death Kraken

[Chaos_Klaus]

You could check out the Kerbal Joint Reinforcement mod. That way you do not need all those struts.

Also, I do not know if the fairing acually makes all these structural wings unfunctional. It could be that your center of lift is above the center of mass and possibly even shifted offcenter. Thats bad. With FAR/NEAR the center of lift should always be behind the center of mass. Note that the center of mass shifts while fuel is burned.

[ghostbuzzer7]

I figured it out. You realize how fast you thrust in the thick atmosphere of Kerbin. By the time you reach 5,000 meters your going more than 600 meters per second.

----Solution-----

Try thrust limiting the rocket and it should fly a bit better and not explode randomly. Ohh and get the module manager patch. keep that updated too.

[Starwhip]

I figured it out. You realize how fast you thrust in the thick atmosphere of Kerbin. By the time you reach 5,000 meters your going more than 600 meters per second.

----Solution-----

Try thrust limiting the rocket and it should fly a bit better and not explode randomly. Ohh and get the module manager patch. keep that updated too.

I'd wager my money on this as well. Too fast for Stock, too fast for Ferram Aerospace Research, just too darn fast in general.

[SaturnianBlue]

I figured it out. You realize how fast you thrust in the thick atmosphere of Kerbin. By the time you reach 5,000 meters your going more than 600 meters per second.

----Solution-----

Try thrust limiting the rocket and it should fly a bit better and not explode randomly. Ohh and get the module manager patch. keep that updated too.

Huh, even when I go 290ms (NEAR) at 5k, it still has problems with control, also, the bug initiates around 900 meters up, but sometimes this differs, as it happened to me at 500m as well.

Edited April 26, 2015 by SaturnianBlue

[ghostbuzzer7]

After looking back at the screenshots, do you have an aerodynamics on it like wings or what not? The solutions are slowly dwindling. Um... you cant gimbal with Solidfuel so refrain from angling with the solidfuel boosters until they decouple (If this works of course). If not, I think that it must have to do with the mods or part clipping.

Happy flying

[SaturnianBlue]

After looking back at the screenshots, do you have an aerodynamics on it like wings or what not? The solutions are slowly dwindling. Um... you cant gimbal with Solidfuel so refrain from angling with the solidfuel boosters until they decouple (If this works of course). If not, I think that it must have to do with the mods or part clipping.

Happy flying

I do have wings as part of the spacecraft structure, and I added some at the bottom as well. It does seem the spacecraft is somewhat more fly able, but much more 6 death prone with more SAS modules. The wing parts that make up the thermal shield are still vulnerable...

Edited April 26, 2015 by SaturnianBlue

[SalehRam]

I figured it out. You realize how fast you thrust in the thick atmosphere of Kerbin. By the time you reach 5,000 meters your going more than 600 meters per second.

----Solution-----

Try thrust limiting the rocket and it should fly a bit better and not explode randomly. Ohh and get the module manager patch. keep that updated too.

Just to confirm this as 99.9% could be the issue.

Going anywhere near 200+m/s below 5000m is going to cause issues, and sometimes some very serious issues (aka. a big fireworks show)...

How I overcome this issue is, by making my TWR during the first stage below 1.5, this way it will guarantee that the rocket will climb high stable enough to gain speed and not blow up, when I reach about 10,000m up, I just put the thrusters to their max, but I still watch out for my gravity turn not to make it so sharp, otherwise I will flip the rocket and lose it...

Try reducing your ascending speed while below 5000m, and make sure it does not climb above 200 m/s, then when above 5000m, you can start increasing your speed until you either reach 10,000m, or you get to the "blue - middle" part of the atmosphere marker, then after that, you can go full thrust...

Also, make sure you have struts for the SRBs, and make sure you watch your angle while ascending, it should be either 0 or 360 degrees, if it goes anywhere around that, then you have a problem in the top of the rocket, which is affecting the overall stability of the rocket.

Edited April 26, 2015 by SalehRam

[SaturnianBlue]

Just to confirm this as 99.9% could be the issue.

Going anywhere near 200+m/s below 5000m is going to cause issues, and sometimes some very serious issues (aka. a big fireworks show)...

How I overcome this issue is, by making my TWR during the first stage below 1.5, this way it will guarantee that the rocket will climb high stable enough to gain speed and not blow up, when I reach about 10,000m up, I just put the thrusters to their max, but I still watch out for my gravity turn not to make it so sharp, otherwise I will flip the rocket and lose it...

Try reducing your ascending speed while below 5000m, and make sure it does not climb above 200 m/s, then when above 5000m, you can start increasing your speed until you either reach 10,000m, or you get to the "blue - middle" part of the atmosphere marker, then after that, you can go full thrust...

Also, make sure you have struts for the SRBs, and make sure you watch your angle while ascending, it should be either 0 or 360 degrees, if it goes anywhere around that, then you have a problem in the top of the rocket, which is affecting the overall stability of the rocket.

Huh, the NEAR aero has no soup sphere, so it natural to go that fast (300 meters per second) I generally start gravity turn at 1 km to 10 km at 40 degrees in NEAR. What confuses me more is the spacecraft breaking partially tearing off, while the Delta 2 rocket is unharmed. I do have 4 struts on each SRB (9 of them) now. It does have a bad case of 6 death kraken too...

Edited April 26, 2015 by SaturnianBlue