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Chik Sneadlov

Shaking on reload. Ditched on Laythe with Ion engines

Question

My ship had no shaking problems last night but when I load today on any of my 3 or 4 saves with this ship it shakes itself to pieces. Very repeatable. Nobody appears to have a solution on the forums so I guess I have to relaunch. I needed to modify the ship anyway. I used autostrut on almost everything and set it to various modes. I also used rigid assembly on a lot of the ship.

The following was written before I encountered the shaking. Ion engines can be useful.

I meant to build a rocket with some ion engines to fine tune navigation, but I ended up with nothing but ion engines for three quarters of the  trip to Laythe. Set a course near Kerbin with the last of my big fuel engines and then found I was 800,000,000 meters off. The sun was pretty dim. I had 20 ion engines and about 12 gigantor solar that were actually getting sunlight. I could leave all the engines on for about 20 seconds and then the batteries would be totally drained. It seemed to take about ten minutes to recharge after turning the whole ship 90 degrees to get a little more light on the panels. Then I'd have to turn the ship back before the 20 second burn. That got very tiresome so I noticed that I was constantly moving closer to my target even with a little thrust in the right direction. Seemed like if I could just keep thrusting a tiny bit for a little more than an hour I'd be able to skim the atmosphere. I ran the engines at about ten percent power and got the ship on course. Dealing with this kind of problem and rationing my thrust seemed very real, very immersive. Very satisfying when my fiddling about actually got me the precision insertion that I wanted. Too bad I didn't know enough about Laythe's atmosphere.

As my course got closer I shut down all but one engine in each pod of five engines, but that was still too much power. I wanted to hit at 15,000 feet because I didn't want to come back out of the atmosphere and smash into Jool which was huge and right in my path. I shutdown all but one of the ions. Oddly, as I thrusted towards my target I was moving away. The engine wasn't on the centerline of the ship so I guess it was rotating it and pushing me in the wrong direction. I activated the other engine across from it and started moving closer to 15,000. Got it to 14,986. That's what the ions are good for, setting up your encounter with the atmosphere and controlling your entry within fifty feet instead of 50,000 feet. I close the solar and communications dish and inflated the heat shield, pointed it prograde. Not very exciting in real time, even when you're between the two huge bodies. I got closer and things went very fast. The heat shield turned red and then the whole rocket turned sideways. Everything started blowing up and blowing away, but then I slowed down and popped one chute. I was heading for the ocean. The chute slowed me down enough for a water landing where I could watch the sky for a few days. Jool took up a huge part of the sky, but I only saw one, tiny moon. It appeared to be circling, but I don't think that's true. Not sure which moon it was. It popped up behind Jool, a small bead, and moved almost vertically.

If I was going to do it again, I'd go for a higher orbit, maybe 25,000 meters or more, maybe even 40,000. try to slow down and get caught in orbit, but not land. Experimenting with this might have been nice but the ship shakes itself to pieces every time I reload now.  I don't think it did that last night. Pretty sure I reloaded last night.

Originally, what I intended to do with this rocket was control my final stage with a mixture of fuel and ion engines. I'd set the engines to different action groups and when I needed a precise atomospheric insertion, I'd turn off the liquid fueled engines and just use the ion engines. Maybe another action group to turn off all but one ion engine. I started work on that but got all confused by fuel flows and the game changing numbers that I'd tediously entered and doing things that weren't intended or making any sense. 

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Shaking solution: on main menu, go to settings, and activate advanced tweakables. Now right click every part of your ship and autostrut it. It reduces wobble or shaking, especially on large, multi-part ship. You can also enforce the connection between parts using strut connector (available on contruction part tab, it's basically duct tape for rockets)

Also, why ion? It has very low thrust and consumes a lot of power (but high efficiency though). It's intended for small satellites or space probes, not for powering the thrust for something that's carrying liquid fuel+oxidizer, fuel is heavy (well, unless you are trying to do something different). If you make a ship with 20 ions and 12 gigantors, I can guess that your ship would be massive (and unsurprisingly, prone to wobble and shaking). Use nuke instead (LV-N engine). It has high efficiency, consumes only liquid fuel (no oxidizer required), still allows precise orbital maneuver and does not need power to operate. The downside is you need to slap some radiator to prevent overheat, and a rather heavy, large profile engine. But still, using nukes, with it's high efficiency, low thrust (but still higher than ions) is still a more reliable choices for interplanetary travel since it considerably reduces part count compared to ion engine-powered ship

Unless you're trying to do something like @Stratzenblitz75. Check out his mission with ion engines:

 

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Autostruts are most likely the problem, not the solution. They can often end up fighting each other. They work great as long as you have a very low number of them -- like five, at most. If you have shaking, it's best to have any autostruts in "grandparent" mode.

 

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3 hours ago, bewing said:

Autostruts are most likely the problem, not the solution.

Maybe, maybe not. At any rate, autostruts are the only means to fix this without reverting to VAB.

@Chik SneadlovIf you have a few moments before things shake themselves to pieces, reach in and try to apply autostruts.  The last time this happened to me, it took like a dozen reloads until I managed to find a piece where they had a useful effect. IIRC it was a "random" part, that is, not one that I would have suspected. Hence the many reloads.

 

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You guys did read the part where the OP said this, "I used autostrut on almost everything and set it to various modes", right?

 

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