Stabilization Help

[Just1ChanceFree]

Not really sure what I'm doing wrong here. SSTO works great up until 10,000m at which point it becomes almost entirely unstable whenever I attempt to make the gravity turn. If I wait until past 30,000m it is completely stable as well, but I don't quite have the fuel differential to wait that long to begin circularizing the orbit. Any ideas why I lose control and how I could fix it? I've done everything I can think of - adding wings to every part, removing parts, ect. Fuel drains out of the top first before the bottom orange tanks and finally the nukes. Main engines are all aerospikes which is part of why control is difficult, but it shouldn't be impossible right? Would SAS or ASAS help? if so, where do I put them? 7 units weren't enough to make me stable (on top of orange tanks and top of rocket). If you want the .craft just ask (uses kethane)

Edited May 2, 2013 by Just1ChanceFree

[Eric S]

The first thing that came to mind looking at that was that those control surfaces should be below your CoM. Having control surfaces above the CoM will result in exactly the kind of problems you're describing, though from your description, it sounds like you put them there after you started having problems.

The second thing I thought was "Huh?" It looks like you've got fuel lines going all over the place. You've got drills on the radial big orange tanks, which isn't a problem, but it really looks like you're trying to asparagus stage engines/tanks that you're not dropping. The extra fuel lines are probably creating fuel loops, which can cause non-symmetrical fuel usage, and that can cause some of the problems you were seeing. However, that source of problems wouldn't happen only when you're doing the gravity turn, so I'm not sure that's the root of the problem.

You should have one fuel line running from each of the orange tanks to the center stack (doesn't matter where you connect to it), and one fuel line running from the center stack to each of the atomic engines (or the fuel tank they're attached to). Yes, that's how the Kethane converter works, with fuel lines from the fuel tank to the converter, if that's why you've got so many extra fuel lines. The converter consumes a negative amount of fuel, so the fuel lines transfer a negative amount of fuel from the tank to the converter.

Also, where's your power to run all those drills and the converter? I see some batteries, but no stock power generation parts. It could be a mod part I'm not recognizing, but I just wanted to check.

[Just1ChanceFree]

I'm realizing I may have loaded the wrong image of the rocket I'm currently working on, the current one has 12x giant solar panels and everything else where it should. Good catch though.

On fuel lines: It was something weird about the kethane mod and this specific design that when I have a fuel line that goes from outside orange tanks into the center converter, it uses the fuel from the top-part orange tank last and makes the whole craft overly top-heavy. As the fuel is currently set up, it does in fact drain from the top first, then the outer orange tanks, and finally the small tanks near the nuke. Not entirely sure why it does work correctly, but I've checked it by right clicking on tanks mid-flight. I think since each of the orange tanks is connected to each other and it won't drain from the same tank twice it will now finally see the top tank as the furthest away from the engines.

On winglets: for some reason when I put winglets on the orange tanks at the bottom it will shift my center of lift outside of the center line (to the left). Even if I place them using the symmetry feature. The original design had 2 at the bottom of each tank on either side of the drill. No dice. It still acted like the top was receiving too much drag while the bottom wasn't experiencing enough air resistance to keep it aligned. My guess is what I'm experiencing is something odd from how the game calculates the drag on parts like the aerospikes.

[mewp]

I've made a video that might actually help a bit here:

..but perhaps you already know what's going on with the COM and COL.

First off, it's ok to put control surfaces ahead of your COM, it is only the static aerodynamic surfaces (wings, fins, etc..) that should be aft of your COM. That being said, control surfaces ahead of your COM should be strictly controlled using ASAS (or some form of control system) as without that they're just the same as a static wing (and thus detract from your stability if they're ahead of the COM).

My first thought about your setup is this: you're using aerospikes, which have no gimbaling ability. As your rocket fly's through the atmosphere your control surfaces slowly become less and less effective - what I suspect is happening is at 10000m or so you're hitting a point at which your forward control surfaces can no longer keep you stable (they just can't grab enough air to keep the rocket stable) and your aerospikes, unlike other engines that can gimbal, aren't doing anything to help keep your rocket in the right direction.

My recommendation: get some more control surfaces aft of your COM, and one thing that should help is having RCS for when you reach higher altitudes. For rockets without gimbaling nozzles there is no form of control when you're in the vacuum of space without RCS and SAS torque (which isn't a whole lot to begin with).

Hope this helps!

[joppiesaus]

Your problem with your SSTO is that the engines have no gimbal. That makes it hard I think. Maybe you can add more control surfaces and a ASAS, and if you use a probe(they can't move very good), try to add some pods, that will work.(maybe it isn't a SSTO anymore )

[magnemoe]

One tips is to turn on rcs just before doing the turn and turn it off afterward. Adding an lander can for more torque might also help, bonus is that it make the ship optionally manned.

Finally never make an loop out of fuel lines, you can however use two lines and make it bidirectional against an central hub.

kerthane generator will feed tanks who are directly attached over or below the generator or connected with an pipe going from tank to generator.

I would used line from upper tanks to the six bottom tanks then to the six small for the nuclear engines and then to the kerthane tank.

Only downside of this is that the top tank would fill first making the ship very top heavy. One change might be to use six small tanks on top of the orange.

[Just1ChanceFree]

Here's some of the mods I've tried based on your recommendations and this is the best I've been able to come up with so far. At 10,000m I shut down aerospikes so I only have the LVT-45s (vectoring) and the nukes (vectoring) running and then turn on RCS before attempting the gravity turn. I'm able to stabilize after spinning laterally about 2160 degrees (6 full revolutions). I still feel like something odd is going on here. Also it is no longer SSTO but that might only be due to steering losses while spinning. You can also see how the center of lift is oddly displaced even though I have added is winglets on the external LVT-45 tanks using symmetry function.

[RoboRay]

Get rid of the fins up on the top of the central tank. They are decreasing your stability.

Also, if your LV-N engines are above the center of mass (it looks like they may be, when you activate them), their gimbals are reversed because KSP assumes that all engines are at the back. This makes them steer away from prograde when you turn on ASAS.

So, either move them down lower or disable their gimbals.

Edited May 2, 2013 by RoboRay

[rryy]

It looks like you're using aerospikes, which for some reason like to make your rocket flip over. Try replacing the aerospikes with the LV-T30s.