Rocking Swaying/Spiralling before kaput

[Jestersage]

So my second attempt+revert of my launch of Nautilus-X clone (while satisfying career contract, hence the ISRU and extra large monoprop tank) on a Jupiter-III clone ended with failure.

This is my craft: http://pastebin.com/S5jeTNYK

Situation: After launch, the rocket begin to rotate or sway quite a bit. I am sure I did not clip anything into it that caused such issue. KER indicate TWR is more than enough with starting at 2.

Proposal

1) MOAR structs? I have heard sometimes moar structs/autostructs causes more issues
2) As of now Jupiter III is a straight clone of Teamvision's proposal, and thus all the first stage thrusters is in the main stack. I actually have a version of Jupiter-III that use conventional-KSP asparagus staging, such that each parallel stage contain a Mammoth.
3) Remove the Nuclear service module and thus decrease weight
4) remove the Senior docks in some area

Question: Which one should I pick?

Sidenote: Jupiter-III design originated from TeamVision's 2006 DIRECT proposal. People speculate the Hab-ring is the only purpose for such Kerbal-like contraption on Earth.

Edited February 26, 2017 by Jestersage

[bewing]

A: your control point is one of the sideways cupolas, which points your navball sideways, which will usually cause your SAS to misbehave.

B: your vector engines are somehow ending up getting heated by exhaust from other engines and blowing up -- which is messing with your thrust vectors and CoM, of course.

C: yes, the top end of your stack is bending and wobbling all over the place. Placing ONE autostrut from the MPL to the Heaviest Part fixed it.

Edited February 26, 2017 by bewing

[Jestersage]

2 minutes ago, bewing said:

A: your control point is one of the sideways cupolas, which points your navball sideways, which will usually cause your SAS to misbehave.

How do I switch it in VAB/Editor?

As for B, I guess that means going back to the conventional Asparagus Staging...

[Mad Rocket Scientist]

11 minutes ago, Jestersage said:

How do I switch it in VAB/Editor?

As for B, I guess that means going back to the conventional Asparagus Staging...

You re-root the craft to a control point that is facing in a normal direction. Re-root is a editor gizmo, I think it's the last one.

[helaeon]

Not really seeing a huge problem with your rocket. I'd just move the SRBs down so all your first stage rocket motors are even. TWR off the pad might be high, so you might want to just keep your throttle down. I usually want to take off at a TWR of about 1.6 and start the gravity turn about 100m/s

With high gimbal engines, sometimes the gimbals point the wrong way when added in symmetry (happens on low gimbal too, but it's not as big of a deal). You might want to add them on one at a time. I'm also seeing too much control authority there. Many of the vibrations are caused by the vectors occillating back and forth setting up a harmonic. Might want to turn down the gimbal range.
Some aero fins are probably a good idea too. Not 100% necessary but I find they can make a big difference, and don't have a huge loss of Delta-V when they don't. I'd put those on the core stage, and two on the drop tanks.

Location of your root part matters too. I've built space stations with their root part far away from the SAS and on the edge of the craft and it vibrates itself apart. If I move the root closer to the center it's better. It's also better if your SAS modules are near the center of the craft as well.
Definitely autostrut across any docking ports or decouplers.

Those LV-Ns should be moved out away from the core of the ship just so those nozzles are clear before decoupling that rhino stage (I'm assuming the reason you did that is because that's not meant to be staged right away, or is meant to be replaced later. If you're not making a replaceable stage use a normal decoupler rather than the seniors)

This thing I'd be using autostruts across any docking ports, and on those boosters and drop tanks. the swaying is from the payload in the fairing, so autostrut that for sure.

For flight I'd use that docking port at the very top as my control point. You just draw the camera inside the fairing and do "control from here" I don't know of a way to change it in the VAB.

Hope that helps Doing the above just real quick I was able to fly it to a 150x150 orbit without too much problem. Little wobbly at the start but then  it's fine. Ended on the Rhino stage with about 1100m/s delta-V

 

[bewing]

Just adding the one autostrut from the MPL enabled me to get it to orbit.

FYI -- your sidesaddle tanks actually run dry just before your kickbacks flame out. So you can actually stage them all at once.

And you don't really need ANY of that monoprop to get to orbit, so it's just wasted mass. (yes I understand you still need the tank) From 40km to 70km it can help keep you facing prograde, though -- so maybe 100 units of it isn't a terrible thing.

Edited February 26, 2017 by bewing

[Jestersage]

The monoprop is for the contract (1650 in your "station"... which is actually a tourist ship o_O) There are no station around Munar orbit, so may as well do the "expansion".

So what I ended up doing is:

• Autostructing to grandparent, especially the area around the ringhub.
• Changed from Jupiter-III "Main-stack-contain-all-thruster" to conventional Aspargus staging. Jupiter-III actually discard the atmo rocket to reveal 5x J-2X (VAC rocket)

though Technically speaking, that will make them into Paris-III. At least that give me an excuse to make the Paris-VII.

Edited February 27, 2017 by Jestersage