What to do when a naughty rocket won't do what it is told?

[space_cowboy]

Hi Rocketeers

I am trying to get a Stayputnik and SC-9001 with a couple of goo units, 2 x Communotron 16 and about 20 z-100 batts to Mun and Minmus Oh and back again. I am using asparagus staging basically a central staging of 2 FL-T800's and an FL-T400 powered with an LV-T45 and LV-909 respectively. This is surrounded with 6 x 2 FL-T800's linked with fuel duct to core staging and powered by LV-T30's however when it comes to doing my gravity turn at 10km it doesnt want to play and goes out of control and I end up ditching most of it in order to recover. I am using SAS but no fins. Any ideas on what I can do to keep this naughty rocket under control?

Even if I do get it back under control and make it into orbit it is normally very inclined and with the core of 2 FL-T800's and an FL-T400 it is very slow to maneuver around the Navball and line up my nodes which means more often than not I miss them or I'll carry out the maneuver even though I'm not aligned and end up just wasting fuel without accomplishing anything.

Would it help my maneuverability to ditch the 1/3 full 2 x FL-T800's and just go straight to my final stage (with larger 800 tank) as soon as I am in orbit around Kerbin?

Is there any trick to finding these nodes quickly on the Nav ball that I'm missing?

Any other tips for controlling a rocket that is reluctant or very slow to comply?

[theend3r]

Is there any trick to finding these nodes quickly on the Nav ball that I'm missing?

Mechjeb's Smart A.S.S. If your craft is too slow I suggest adding more control surfaces for atmosphere and more RCS thrusters (and tanks if needed) for space.

[Whirligig Girl]

A naughty rocket? Oh my... DO you have any SAS modules or RCS?

[qromodynmc]

Add more rcs,and more control surfaces.

[SkyRender]

Providing the .craft file would help with diagnosing the problem. Often it's possible to figure out if it's a design flaw or a problem in lifting technique by observing the vessel in question.

[Tank Buddy]

As usual, photos would help. Take a screen shot, upload it to an image hosting site, like imgur, and put the URL in BB code. Imgur gives you this format, so you can just copy it from the dialog box that pops up by clicking on the image.

From the sound of it, you need some gimbaling engines and/or more reaction wheels. Your orbit is inclined most likely because your "naughty" rocket lacks controllability. If you need to turn while in orbit and reaction wheels won't suffice, use RCS.

[Pecan]

I am trying to get a Stayputnik and SC-9001 with a couple of goo units, 2 x Communotron 16 and about 20 z-100 batts to Mun and Minmus Oh and back again. I am using asparagus staging basically a central staging of 2 FL-T800's and an FL-T400 powered with an LV-T45 and LV-909 respectively. This is surrounded with 6 x 2 FL-T800's linked with fuel duct to core staging and powered by LV-T30's

If the 6 sets of tanks + T30s are all connected to the core stage then that's not asparagus and will be fairly inefficient. With 7 asparagus stacks the first two to be jettisoned feed fuel to the next two, which feed to the next (penultimate drop) two, which feed to the core. Thus the fuel runs through all of them to the core and the outside ones are emptied and jettisoned quickly.

There is no point in carrying multiple communitrons as they are resusable. Similarly, if you have large batteries than the z-100 they will mass the same for a given capacity but incur lower drag. On the other hand, if you have solar panels just one fixed one and a battery will be all you need.

I'm just going to build what I think you mean to see how it goes ...

ETA: Yes, it's a pig isn't it! It behaved well during the ascent but once it was drifting engine-off to the cicularisation burn I couldn't get it lined-up at all, despite leaning on the key for nearly 30 seconds^^. Adding an ASAS unit between (I assume) the SC-9001 and FL-T400 sorts it out nicely. Your design is otherwise sound, a standard ascent using a 10km gravity turn puts it in orbit with over 5km/s deltaV left. It might be a bit over-powered but that's better than the alternative.

Edited February 11, 2014 by Pecan

[SRV Ron]

Try a payload like this which was sent to Eve, Duna, and Laythe.

Note, one SAS module will be more then enough to control this Career Mode launch vehicle.

Edited February 10, 2014 by SRV Ron

[Kryxal]

I've noticed a tendency for my craft with 6-tank asparagus staging to rotate once they drop the first pair of asparagus tanks, might this be similar? I usually mount extra SAS on the final two asparagus tanks and just live with it ... and maybe throttle down a a bit when the spin gets a bit much. If it's a similar problem, start your gravity turn early and make it shallow, don't try to maneuver in an excessive spin, and just fix things once you steady out.

[Pecan]

One SAS should be enough for this sort of sized vehicle. Better ways to reduce (can be impossible to remove) roll are to add struts so nothing is wobbling around - look at SRV Ron's - and, possibly, aerodynamic surfaces/fins. Personally I've never used those and haven't needed to, struts have always been enough.

[space_cowboy]

Thank you for your replies.

Apologies...What a nab I am...I feel a little bit silly This was my first attempt at a rocket with more than 6 x FL-T800 fuel tanks and I just expected the Stayputniks built in RCS to do the job as it has always done up till now. I never even considered that adding a reaction wheel would make all the difference, but obviously that was what was required for a rocket this size.

I was at work so no access to screenshots and I got myself a bit confused. After my failures with this in career mode I had been messing with this build in the sandbox trying to improve it forgetting I dont have the fuel ducting in career mode yet. So yes the original was not proper asparagus staging it was just those 6 x 2 800's as an initial boost stage to get to my gravity turn.

Now I just gotta work on getting more Kerbin based science done till I get some solar panels as even 24 Z-100's are enough to get my science back from Mun.

Thanks again

Edited February 11, 2014 by space_cowboy

[SRV Ron]

Check out the bracing pattern in the design without the SRB ring. Note, only the one SAS is needed. Spin is all but eliminated;

What little spin that does occur is easily controlled by the q and e key.

[Lunknumb]

The Stayputnic has a very tiny amount of torque compared to any alternative.

So yea, an extra reaction wheels below the final stage is always a good thing with it.

[AletzN1]

Pics, gotta hav'em! Apparently most don't know how to get'em. F1 if you didn't know.

O and yeah SAS gotta hav'em aswell.