Help in adapting to 1.0

[davidpsummers]

I was trying lift a space station module into orbit. I made a design as I would have for 0.9 (see below, it does, in fact, launch fine in 0.9). However, in 1.0 it has all sorts of problems. It looses stability (even at moderate TWR). (Somewhat around 8km to 15 km.) I also had a huge problem with the first stage of the central stack overheating.

Now the point of 1.0 is that it is suppose to be different. My problem is that I don't understand what is going wrong. What is the source of the instability? Why is the rocket overheating?

Any help would be great.

Edited June 7, 2015 by davidpsummers

[imaspacestation]

You ought to re-think your rocket designs. Long and sleek. Flat and broad no longer works.

Your stability problems are due to drag. If you push your angle of attack too hard on your turns, you will stall and spin out.

[capi3101]

Do me a quick favor - go back into the VAB and take another screenie with the CoM indicator turned on. Drag is indeed the issue.

A big contributing factor is the position of the CoM. If I'm looking at your first screenie correctly, your payload (the station core) is about 25 tonnes all told, tops. So that means out of your 337 tonne tocket, the vast majority of it is in the rear. You've also got waaaaaay more thrust than you need at this point; 1.5 at launch is plenty.

What's going on is the old "throw a dart backwards" problem - you need the majority of your mass up near the top. Failing that, you need fins down towards the bottom. Now, you have them, but look where they're attached - to those SRBs, which you're getting rid of toot-sweet. Fins on your LF tanks would help matters tremendously.

I might suggest you look at the Optimal Rocket Calculator for KSP 1.0 site; it'll help you out with designing a more reliable booster better suited for the new drag conditions. As for flying - stay going straight to 5k, then slowly begin to pitch over; have your nose pointed at 45 degrees by 15k (instead of shooting over hard to 45 degrees at 10k - doing that's gonna kill ya in 1.0.x). After that, it should be the same as it was pre-1.0.

Edited June 4, 2015 by capi3101

[EtherDragon]

Even better, any chance of getting a YouTube of a launch?

[11of10]

Reduce your TWR on the pad, you really don't need 2.06.

[Prepper-Jack]

In addition to what was said above..

As for the engine overheating - it seems to be one of the traits of the Twin Boar. It's not as noticeable if used as a single stage, but it will get quite hot in asparagus staging as it runs longer.

For aerodynamics, consider something other than the large cones for your big orange rockomax tanks. They're apparently no better than a flat surface at the moment, and this may be causing significant drag issues.

Otherwise, what speeds are you hitting at the flip altitude? For stability on large loads, I've been trying to keep things only a little above 300 m/s below 10k, max of around 500 m/s by 15k, and max of 800 or 900 at 20k.

Are you heading straight up, or doing a gravity turn? Large and long, unaerodynamic loads may benefit from later turns (where there is less air). Aerodynamic shear can cause massive instability if you step outside the prograde vector with such a craft (even sometimes within the circle itself).

Are those control surface wings on the bottom (it's a bit hard to tell)? Between engine gimbal, electronic steering, and control surface - the SAS may not be able to handle it, and you'll begin to wobble back and forth as it overcompensates every movement. Try deactivating gimbal, or electronic steering, or replacing fins with some immobile wing.

[davidpsummers]

You ought to re-think your rocket designs. Long and sleek. Flat and broad no longer works.

Your stability problems are due to drag. If you push your angle of attack too hard on your turns, you will stall and spin out.

I'm not clear one why long and sleek is better. They do have less over all drag, but the drag occurs at the "front" (ie the top). If you make the rocket long, you give that drag a nice long lever arm to spin your rock with.

(note: I was being very gentle on the angle of attack, in fact, one problem occurred when the started to loose control in a direct perpendicular to the direction I neede to lean the rocket over at).

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Note, that TWR is at full throttle. When I actually launch, I go full up to about 100m/s, then I pull back to a TWR of about 1.4-1.7.

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The COM is indeed low, I will post a picture below.

I have fins on the central stack also (and the liquid boosters). I was worried the fins on the inner parts wouldn't help until the boosters dropped away and they were better exposed to the airflow, so I stuck another set on the boosters.

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Note: I'll look to see if I have a video of the failure. I have some, but in some of them (I tried 3 times before getting to orbit more by luck than anything) I made mistakes I do understand.

[davidpsummers]

OK, I tried a launch. It actually worked, but showed some of my problems.

https://www.dropbox.com/s/t59d83rm7nv8r99/Screen%20Recording%203.mov?dl=0

At about 5,000 m I have a lot of "wobble" problems. The rocket is not esp. wobbly in 0.90. I don't know if it is "real wobble" or starting to have control problems.

In one failed attempt, I tried no turning until I was up around 30,000m (ie basically up out of the all the atmosphere and drag), but I lost it before I got there because I couldn't control the wobble/control.

I'm late with my turn. (Because of the problems). I try and turn slowly but I struggle not to loose while turning at a rate that would get me over enough (I am late, but I tried to turn at a rate I would have if I wasn't late in turning). Also, I don't just struggle to control it in the direct of the turn, I also encounter significant control deviations north/south.

[mrclucks]

In my expirence I have greater success with com being closer to the top or middle rather than the bottom.

Try stacking another orange fuel container on top of your asperagaus staging and get rid of your solid boosters, so your rocket is more triangle shaped and less T shaped.

I see you have an engine staged with radial decouplers which I will assume is your bottom slcenter engine. Try staging it with the rest of your liquid rocket boosters for more twr control.

Lastly you could take off your puny wings and add larger wings to help with stability and heat. Reduce gimbal to 50 for your central engine, disable for the outer engines and add control surfaces to the end of your wings.

[davidpsummers]

Regarding the COM. Long rockets are wobbly. One reason I went to this was that I had hit a limit with how much dV I could get before the thing just wobble too much. But apparently it doesn't take too much asparagus staging before you have control problem? So the answer is you need more science to get the bigger tanks and engines?

[guitarxe]

Drop me a craft file of your monstrosity. I'll see if it can get to orbit and show you how to fly it if it can. I'll also show you how you can redesign it to fly much easier (and probably cheaper, too).

[FancyMouse]

Wobbling does not directly come from how long the rocket is, but rather how many parts are stacked. I can stack dozens of batteries that wobble like crazy even if it's shorter than normal fuel tanks.

And it does seem that your main stack has too many parts - you indeed need to do some structural enforcement.

[cybersol]

Tip I haven't seen mentioned here:

Don't use SAS on long (many part) rockets with weak joints until you get above 40km.

Really, you should not need SAS very much at all during the gravity turn. If you have so much control that the rocket is twitchy when flown manually without SAS, then reduce gimbal, wheels, or even swap some control fins for stabilizing (lift-only) fins.

[Harry Rhodan]

I'm not clear one why long and sleek is better. They do have less over all drag, but the drag occurs at the "front" (ie the top). If you make the rocket long, you give that drag a nice long lever arm to spin your rock with.

Because your lever will rotate around the CoM which will always be extremely low with pancake lifters.

[Whippler]

Those look like control surface wings. Use static wings to reduce the wobble, and have thrust vectoring/gimbal only enabled on the main center rocket. Also when it starts to wobble, just disable SAS for a bit and keep the rocket straight yourself using wasd, wobling should calm down.

This monstrosity i created for a space station contract (8 seats + ISRU + science module + have over 6000 Lf left on Minmus orbit). Ascend went pretty well. Just wait until 15-20k altitude to start the gravity turn. Some extra parachutes for early stage recovery mod in there.

Edited June 5, 2015 by Whippler

[capi3101]

Watching your YouTube video, OP. So this is going to read like a running commentary.

Just out of curiosity - is there any reason why you have your launch clamps in a stage other than the initial stage? You do know they'll work just as well if you let them loose at the same time you light your rockets up (and you won't blow up your launchpad in the process). Seriously - if you've never tried it before, put the launch clamps in the bottom stage. I guarantee you that you won't be disappointed. Unless for some reason you forget to throttle up first...

The nosecones on the bottoms of the internal booster units are a complete waste of mass. Just saying.

You should not be getting your gee meter that high that early in your flight. Too much thrust - you're losing delta-V to excessive drag. 100 m/s by 1000 meters was good enough even in the old soup.

Floppy rocket beginning around 2500; you start fiddling with the gimbal controls. Struts between the boosters and the payload would help here. A fairing covering the entire payload would also not go amiss (I don't know if you can do that or not in 1.0.x, though - I use Procedural Fairings and haven't bothered with the new stock fairings at all, so I don't know how they work). It also looks to me like you're using a fairing to connect the payload to the booster; I'll go ahead and tell you that it doesn't really work - you still need good old-fashioned space tape to keep things steady when you're connecting things up around a narrow little point (like, for example, a Clamp-O-Tron).

You should be starting your turn sooner, though given your stability issues I certainly understand why you'd want to hesitate...

Floppy rocket stops around 15k. By 20k you're 50 seconds to Ap; I'd ordinarily be flying about 20 degrees above the horizon at that point trying to pick up horizontal velocity. You've definitely got enough vertical velocity to coast up for a bit.

27,000 you cut lose the second stage and light the twin boar. There's another source of instability there - you don't light a central engine up until that point.

35,000 and the video stops.

----

Okay, so summary then - a big part of your problem is bad asparagus, made worse by the changes to the aero model in 1.0.x.

You can still go with an asparagus design, but you'll need to re-engineer it for your payload, which in my previous post I figured was somewhere in the neighborhood of 25 tonnes. If you go with Temstar's Guidelines for Asparagus (which are still valid for 1.0.x despite the vast number of changes to the game since they were written way back in 0.21), a 25 tonne payload can be lifted with a 166.67 tonne rocket. You need 1.5 TWR on the launchpad, so calculate that and you get 2450 kN of thrust - that's all you need on the pad. Now you put 22% of that in the core - 539 kN - and take the other 78% - 1911 kN - and distribute it among...let's go with three booster pairs...so six more engines - so that comes out to 318 kN a piece. Pick a set of engines capable of that level of thrust - Skippers all around - and now tune them to the appropriate thrust levels, about 83% for the core engine and 49% for the side boosters. Seven skippers weigh 21 tonnes total and your payload is 25 tonnes, which means out of your 166.67 tonne mass budget, you've still got 120.67 tonnes for fins, nosecones, decouplers and fuel. Let's say 6 Protective Nose Cones, 6 TT-78s, a Rockomax Decoupler, and six Tail Fins (which move nowadays and make excellent fins IMHO). That comes out to 2.68 tonnes, so let's just round up and say three tonnes for sundry junk. You've got 117.67 tonnes left for fuel - which you divide evenly into seven stacks. That comes out to 16.81 tonnes of fuel each...so let's look and see here......X200-32 tanks hold 18 tonnes of fuel. What you could do there is go ahead and use just one X200-32 tank per stack and then up the thrust on each engine to compensate for the slightly higher than needed fuel amount, or go ahead and drain down each tank to 1345 LF and 1644 LOX.

Now, long rocket designs - why would one be better? Less overall drag for one. Less cost for another. Lower part count for yet another. If they're floppy, add more struts; there used to be an old trick where you could put Cubic Octagonal Struts out on the sides of a stack decoupler and a matching set above, and then connect them with space tape - you could try that to see if it'd shore up the connections and make the rocket sturdier. If you wont have them, you could go with Modular Girder Segments instead (though those would add mass so don't go nuts with them). First solution of the Calculator says - Rockomax Brand Decoupler, Rockomax X200-8 Fuel Tank, Rockomax X200-16 Fuel Tank, RE-I5 "Skipper" Liquid Fuel Engine; then TR-38-D, Kerbodyne S3-3600 Tank, Kerbodyne S3-14400 Tank, Kerbodyne KR-2L+ "Rhino" Liquid Fuel Engine. And that's it. 4,040 ms of delta-V, √46050, 16.4% payload fraction. Good design if you've got the tech. Add a few fins to the bottom stage to keep the rocket steady.

As for keeping the mass of the rocket up higher, that goes back to the physics of levers. For the basics, I'll direct you to

- and don't laugh at the haircuts, pay attention to what he's talking about. A rocket is a lever, and the CoM is its fulcrum point. The end of the rocket that's got the bulk of the mass - that's the one that takes more force to move around. Edited June 5, 2015 by capi3101

[davidpsummers]

Tip I haven't seen mentioned here:

Don't use SAS on long (many part) rockets with weak joints until you get above 40km.

Really, you should not need SAS very much at all during the gravity turn. If you have so much control that the rocket is twitchy when flown manually without SAS, then reduce gimbal, wheels, or even swap some control fins for stabilizing (lift-only) fins.

I'll try not using SAS. I'm in habit from small rockets, but since large ones take a lot more effort to turn.

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Because your lever will rotate around the CoM which will always be extremely low with pancake lifters.

Well maybe that is one of my problems. I picture the rocket being pushed at one end (by the rockets) and the other end (by the drag at the front). But I guess the rockets alway (absent gimgaling) push in line with the rocket, so it is drag in front vs. COM?

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Those look like control surface wings. Use static wings to reduce the wobble, and have thrust vectoring/gimbal only enabled on the main center rocket. Also when it starts to wobble, just disable SAS for a bit and keep the rocket straight yourself using wasd, wobling should calm down.

This monstrosity i created for a space station contract (8 seats + ISRU + science module + have over 6000 Lf left on Minmus orbit). Ascend went pretty well. Just wait until 15-20k altitude to start the gravity turn. Some extra parachutes for early stage recovery mod in there.

http://puu.sh/iaP28/1b71e54663.jpg

There are enough sources of wobble, that I never know what to look at first. I'll check these out.

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Drop me a craft file of your monstrosity. I'll see if it can get to orbit and show you how to fly it if it can. I'll also show you how you can redesign it to fly much easier (and probably cheaper, too).

Note, I've gotten it into orbit and what I'm looking to do is learn why it was so hard and I failed multiple times, rather than about making this one rocket work. But it is not a bad idea to post the craft file for general advice.

https://www.dropbox.com/s/fctxjwpa5vjivq4/Galileo%20Station%20v7.craft?dl=0

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On the comments about the video, thanks. I'll digest them, on some specific questions....

"Just out of curiosity - is there any reason why you have your launch clamps in a stage other than the initial stage?"

There is that jerk when the solids light up. This lets me give it a second to let the worst of that dampen. Don't really need it here, but I've found it useful.

"The nosecones on the bottoms of the internal booster units are a complete waste of mass. Just saying."

It looks better.

"27,000 you cut lose the second stage and light the twin boar. There's another source of instability there - you don't light a central engine up until that point."

Why? Does the central engine give more stability than radially mounted ones?

"35,000 and the video stops."

My apoapsis was high enough that I could cost up and burn to reach orbit. (Or would have been in just a few seconds, don't recall correctly.) Since that is a trivial exercise, I called the launch successful at that point.

"If you go with Temstar's Guidelines for Asparagus (which are still valid for 1.0.x despite the vast number of changes to the game since they were written way back in 0.21), a 25 tonne payload can be lifted with a 166.67 tonne rocket. "

I'll check it out.

Some good tips on how to strengthen a single stack. I has assumed I just had to live with it.

Edited June 5, 2015 by davidpsummers

[MarvinKitFox]

Ok, took a look at your file.

Here it is back, with the bare minimum changes.

This is now solid as a rock!

https://www.dropbox.com/s/pe5mh5fbo6yl6lw/Galileo%20Station%20v8.craft?dl=0

Never mind the CoM vs Drag issues.

Never mind the excessive TWR

Never mind the cute but ridiculous reversed-nosecones on your drop tanks.

The only insoluble problem with this ship is that you are a poor seamstress.

Meaning, you do not use struts correctly.

changes:

I removed your monkey-cage struts from around your hourglass, and replaced it with cross-strutting.

I added 1 strut from each outboard tank to the core

I added 3 struts to the top probe, it was bobbling.

Total addition:9 struts.

I have also moved your launch clamps to first stage, this is a stylistic preference of mine. move em back if you wish.

Try it please.

[davidpsummers]

I give your changes a try. It is good to know that the cross struts work better.

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So I guess, other than the struts, the main lesson is don't let your COM get too low and limit the use of fins for active control.

[cybersol]

The only insoluble problem with this ship is that you are a poor seamstress.

Meaning, you do not use struts correctly.

Struts are an art form, and I find there is always more to learn. I rewired it the way I would have currently struted it and ended up with 34 fewer struts. I also ditched the interstage fairing which did not seem to reduce drag and the BACC control fins. Personally, I would lose the BACCs entirely as they are nerf-tastic in 1.0. The craft file is here.

...and limit the use of fins for active control.

IMO, if you need fins then control fins will do the anti-spinning job better with less mass than other mere lifting surfaces. The one time I found if can make sense to have non-control lift is when you need to counter higher up lift (wings, radiators) and already have too much control (symptom is SAS freaking out).

[davidpsummers]

So control fins on the central stack, slipped in between boosters, are as effective as ones mounted on the out most boosters?

[cybersol]

Good question. Control fins on the outside and further are away from the center of mass are more effective. However, your BACC booster stage is so short in burn time that those fins are not carrying their weight. To be honest, the BACCs themselves are probably not carrying their weight. Confession that I might be biased since I started a thread about how SRBs were overly nerfed in 1.0 (BACCs got 15% less Isp in a relative sense to most LFO engines, 30% less burn time, and 50% increased cost).