extra long parts .... how to gravity turn?

[mellojoe]

Every attempt I've made to launch a habitat arm for my space station attempt has failed. I cannot seem to make a long arm get into orbit. Essentially what is happening is that as I go for gravity turn, the whole thing goes arse-over-teakettle. I've tried putting more RCS thrusters near the top. I've even put small actual thrusters near the top. I've stabilized the thing with girders and struts, so it doesn't wobble. I can fly the thing straight up no problem. As soon as the engines go a little sidways for a turn, however, spinning ball of death.

I've tried an early, gradual turn at around 5k meters. I've tried waiting until 25k meters, dropping 2nd stage, and relying only on 3 of the 7 (asparagus staged) mainsails.

Is there a trick to launching these long parts? Seems like everyone else has managed it.

I guess I can split it in half and use docking clams to connect it in space. But that means double the launches and double the docking...

[rryy]

Pictures please?

Try attaching the lifter radially to the payload. This should make it shorter, wider, and more stable. Also, try starting your gravity turn early and do it gradually during your ascent, keeping close to the surface prograde.

[whatisthisidonteven]

If it's that long, you could try building the rocket around the arm instead of underneath it. Another thing you could try is rotating the arm on its side and building the rocket underneath it as opposed to launching the arm in a vertical position.

[Mr Shifty]

Do you have air control surfaces on the rockets? Put one winglet each, radially outward, near the base of each of the outer rockets. Then put 4 more symmetrically around the base of your inner rocket.

Make sure you've got RCS thrusters near the top and the bottom of your inner rocket stage. That way, it can use them to pivot around the center of mass.

Also, lock the gimbals on all of the mainsails except your innermost rocket.

Here's my long rocket. I launch with 4 asparagus connected mainsail+2 orange tank boosters clustered around the outside. I have no control issues until the last set of boosters falls away, then I have to turn on RCS to make it turnable.

Edited June 13, 2013 by Mr Shifty

[steffen_anywhere]

And if launching in one part does not work at all, split it in three and use a tricoupler. This way you get a compact package, which you can then "unpack in orbit". Then just assemble it

PS: Don't forget to equip every armpiece with a probe core and am RCS system, otherwise you will find yourself cursing, deorbiting the whole thing and starting allover again as you cant assemble it.

If you want to attach the arm to a space station, then I suggest rendevousing the package with the station and then unpacking it and docking the arm piece by piece.

[kinnison]

one trick that worked for me was to click on something at the tip of the rocket and "Control from here". no idea if it will help you, but maybe the game needs to know which part is pointed up

[iEvermore]

Pics please. Also, seems your doing this manually, just confirm you are not using Mecheb.

Make sure you check where your center of mass is. If it's above the half way mark that's your problem. In VAB, take off the stages up to where you normally get the problem, (ie: if stage 3 is your problem, click and drag off only stages 1 and 2), then check your center of mass, it will be different than checking your craft as a whole. If so, adjust the ship to bring the center of mass below the half way mark of the ship. Also, try some winglets. I'm sure COM is your problem though. Happened to me enough.

[mellojoe]

I'm at work currently (shhhhhhhh, don't tell anyone I'm looking at spaceships at my desk). But when I get home, I'll snap a screenshot.

I tried using MechJeb, but that kept failling, so I've been attempting to launch manually. My main idea was to get a decent launch system, save it into Subassembly, and then just pull it out and strap anything to it. I finally got a launch system that did well (I thought) and had it all stitched together with struts for stability, parachutes on the stages, and even a probe body on the main seperator so that I could always deorbit it to return to Kerbin. I mean I had FINALLY built something with some sense of realism. And now it looks like it won't work.

I'll grab some screenies at home and post them up tonight.

[iEvermore]

I have a few lifters that I can use for most payloads. However in some cases it's better to build your lifting stage around your payload instead of under as rryy mentioned. Sometimes too tall is your problem.

[maackey]

Long ships have more mass at the bottom usually, which means more drag at the top. Imagine trying to parachute down from a plane, but with the (rigid) parachute out below you. You want to keep your attitude as close to the prograde vector as possible until you get out of the atmosphere, no more than 5 degrees maximum, and even that is pushing it at significant speeds. Control surfaces as low or high as possible will help a little as well.

Alternatively you can try to place your payload in between two lifter stacks instead of on top. I typically don't like to do this as I use subassembly and FAR, which means I can re-use realistic rockets without re-designing the lifter stage every time, but if the payload is large enough you save a lot more time building a custom lifter stage than trying to fly perfectly.

[mellojoe]

I've successfully launched it. I added a TON more bracing, and then just took the gravity turn as slow as humanly possible. Really went little by little. That did the trick.

Here are some screenshots:

Here is my heavy lifter base, with a Minmus lander on top. This thing was a piece of cake to launch, and everything was perfecto.

Here is the habitat module with arms and docking tug that I have been trying to launch. Nothing too extreme I thought.

Here's a shot of my success so far. You can see the rib-cage of struts I put around the central stalk. It kept breaking on my near-successes, so this rib-cage tied everything together.

So, it is sort of working. Just looks REAL UGLY doing it.