Can't get this into Orbit

[scola_p]

Hi All,

I am in the process of trying to build a surface base for the Mun for a contract, but rather than just send up a once piece tall base, I wanted to do something a little more special.

I am planing on a cupola (contractual) and a hitchiker in the central bit with 4 docking ports on the sides, to which I attach 3 sideways R-32s with landing legs and thuds and a MPL sideways with the same legs and engines.

However, when trying to get my R-32s into orbit (one at a time) I just keep flipping over once I get to about 10 degrees pitch. And it doesn't matter how slow or fast I go up or pitch over.

Can someone please tell me what I am doing wrong? I have attached the .craft file here: https://drive.google.com/open?id=0Bw4vIGGr3npPLXF4aVl3SGEzenc&authuser=0. I also have KER on the ship. Not sure if that will break it for non-KER installs.

Thanks in advance,

P

Edited June 5, 2015 by scola_p

[Vanamonde]

It's probably the usual front-loaded drag issue. How about some pics of the ship?

[capi3101]

I'd be willing to take a look at it for you; I've sent an access request.

Meantime, let's talk about your setup. What aerodynamics are you using? Are you using stock fairings, procedural fairings, or sitting there wondering "what's a fairing"? (Just trying to eliminate that as a potential source of your problems there; not trying to be a wise-ass...). I'm assuming your booster is attached to your payload in your craft file; I'll know more about it when I can get access. Could be something as simple as insufficient nose-cones or fins on the booster, or it could be that the mass of the booster is greater than the mass of your payload...you are trying to lift a payload in the vicinity of twenty tonnes, after all, just from the description.

Not sure if it's entirely necessary, but if I understand your grand master plan here, you might want to be sure to include some lander legs for your core. That way the completed structure is fully supported once it's on the ground.

[Justicier]

I'm unable to get the craft file, but I may be able to talk through the issue. Does the lifting rocket use winglets? Is the payload encased in a fairing? Do you pitch over the rocket slightly after clearing the launch clamps? (or right after liftoff to clear the pad) At what point are you starting your gravity turn?

There's a bunch of things that could be going wrong, but in my own experience 9 times out of 10 when my rocket flips out it's due to poor ascent profile. Its a delicate balance because I have had rockets that if I were to launch and perform NO gravity turn and just keep it pointed straight up, it'll flip every time. But... with the same rocket, if I pitch over a few degrees at the pad just after liftoff to prevent possible damage to KSC and also to build up some lateral momentum to the rocket... it doesn't flip at all when I start my gravity turn at 30,000m. Its really tricky to diagnose since I am essentially flying blind.

[scola_p]

I have just made the file available to all. Didn't know you had to do that with Google Drive!

All my parts are stock, and I have a 2.5m fairing around my payload and the pilots return ship.

Under that i have a central mainsail with 2 R-64 tanks, and 4 onion staged mainsails with 2 R-64s again.

I know my ascent profiles are often less than perfect, so I bring extra delta-v to the party.

There is a tug by my station for assembling things.

Shut down for the night, so I can't post any pics.

Thanks,

P

[capi3101]

Vanamonde called it - for the size of the booster, you don't have nearly enough drag-producing parts in the rear. Your CoM shifts towards the rocket in flight, and it becomes a dart thrown backwards; aerodynamic forces spin the wrong end towards space. Moar fins if you want to keep this design. Especially on that core stage...

The booster is definitely over-engineered as well; you don't need five mainsails and a 415 tonne rocket to lift twenty tonnes (unless you're trying to do it SSTO, in which case more power to you; keep adjusting your throttle down in flight once you've made your turn so that your G meter is at the top of the green and you're golden). A good asparagus design would get that up into orbit - the rocket would have a mass of just over 130 tonnes and it'd require 1960 kN of thrust at launch. Though they're quite old now, '>Temstar's guidelines for asparagus are still largely valid; the main differences these days are that you want to shoot for a launchpad TWR of 1.5 in stock (1.2 in FAR) and that nosecones and fins are no longer just a good suggestion. And of course, there's nothing wrong with a serial-staged rocket either, depending on how far up the tech tree you are (the serial staged rocket would almost definitely reduce any problems you have with tumble, as by their very nature the mass of serial rockets stays up towards the nose).

Edited June 3, 2015 by capi3101

[scola_p]

Ahhhh!

My smaller rockets had noodle based problems with extra fins, so I was trying to avoid overdoing the controls.

I will pop some more on and see about reducing the insane liquid boosters to something more cost effective!

Of course, I will post updates when I can. The delta-v sp spreadsheet I have at work will see some use today!

Thanks,

P

[Kryxal]

If you want to avoid over-controlling, use some of the non-control fins ... honestly, I'd consider dropping the side stacks to one orange tank and a skipper each, and using pairwise asparagus.

[capi3101]

^^

This. Though if you wanted to keep it at two booster pairs (five engines total), you'd be able to do the job with an X200-32 in each of the five stacks; change it to three booster pairs (seven engines total) and you could get that down to an X200-16/X200-8 combo easily enough. Plus nosecones and fins and whatnot.

--Asparagus--

Five engines (all Skippers): set the center to 68% thrust and the side engines to 60%. An x200-32 in each stack.

Seven engines (all Skippers): set the center to 68% and the side engines to 40%. An x200-16 and x200-8 in each stack.

Nine engines: The center is still a Skipper set at 68%, but the side engines become Swivels (LV-T45s) set at 100%. The center stack remains an x200-16 and x200-8; the side stacks become two FL-T800s, an FL-T400 and an FL-T100 each.

Couldn't tell you which is the least expensive option...

Then here's a two-stage serial option:

Upper stage: Rockomax Decoupler, X200-32, X200-16, Skipper Engine - 1751.837 m/s, 1.33 TWR

Lower Stage: Rockomax Decoupler, Jumbo64, X200-32, X200-16, Mainsail Engine - 1752.212, 1.30 TWR

Takeoff Mass: 118.2925 tonnes

You'd need fins on the lower stage to keep the rocket steady on course as you approached first stage seperation, which would cut into the TWR a little bit more than what I've calculated here. The TWRs of the design are sub-optimal, but not so low that you wouldn't make orbit. Beauty of the serial design - it's simple, and you wouldn't need nosecones.

Edited June 3, 2015 by capi3101

[Dilli]

I'd put 4 way symmetry delta wings on the core of the first stage - they make good fins; surprisingly I have not had a problem with them being hit by the side boosters on separation in similar setups.

[Acet]

To lift 20t in payload all you need is 1 orange tank with a Skipper under it and 8 side columns of FL-T fuel tanks with a reliant engine under each, paired in an asparagus configuration. Personally I add chutes to the first two or three asparagus booster pairs dropped to try and get some credits back.

This can be scaled up all the way to 35t payloads by replacing the Skipper with a Mainsail, and adding more fuel tanks to both the side columns and the central core.

The equivalent is a central core with an orange tank and a Mainsail and two side boosters made from one orange tank and a Skipper each, but this is slightly more expensive, though less complex.

[Mister Dilsby]

Lots of good stuff on this 'how not to flip' thread, general techniques I and others have used to solve various launch stability problems.

[scola_p]

Thanks for your help, one and all!

I didn't get time for more than a quick fiddle last night, but I did change to asparagus staging and cut down to R-32 tanks and almost made it to orbit until I got spacebar happy.

I also discovered that time warping on the launch pad waiting for a good orbital rendezvous summons a very explosive kraken!

P

[capi3101]

It can summon the Kraken for sure. Launch clamps usually help with that, as does putting moving your rocket up and down in the VAB such that the engines are slightly buried in the floor; the game will automatically set the bottom of them directly on the pad when you go out there.

[scola_p]

Obviously I forgot to stage my clamps properly, so two of my side boosters came off at launch...

P

[capi3101]

Obviously I forgot to stage my clamps properly, so two of my side boosters came off at launch...

P

Not much you can do there besides cut loose with an annoyed grunt, hit "Revert to VAB" and fix it...

Been there. I think there are very few here that haven't been at one point or another...

[scola_p]

Well, it is in orbit!

Massively cut down and with Big old wings on my central fuel tank.

Now I just need to dock it!

Not in front of KSP, but I will update with pics later.

Thanks everyone!!

P