Need advice on how to get this to orbit.

[zeanomourph]

Hey all, I know it's kinda frowned on asking people to help design a rocket because that's half the fun of the game.. but I'm really stuck with this one. I spent about 7 hours last night trying to get it into space with probably 20+ different launch stacks and didn't even come close, not a single one got it above 10km before I totally lost control and started flipping around like crazy. Tried everything from smallish rockets with super slow acceleration to crazy overpowered beasts pushing it up at over 5G's, SRB's, asparagus, no fins, some fins, crazy amounts of fins, with and without aero nose cone fairings over the whole thing.. I just don't know what to do short of having to redesign the whole segment from scratch, which I'd really rather not do because I spent a lot of time on it and think it looks pretty cool.

I need (/want) to get it up to a station I'm building in a 450km circular orbit around Kerbin, should be able to handle it once I get it to orbit but I just haven't even been able to get it close, I've got intercepting and docking pretty much down to an art by now but this is my first time trying to launch something this heavy (I've already dumped half the fuel out of every tank on it because I can refill them once I get it connected to the station). I know it can be done because I've seen videos of people launching things much bulkier and lopsided, this is all done with symmetry except for a single Jr Docking Port (0.02t IIRC) on the back of the capsule (for an escape pod).

Running the game 100% stock 1.1.3 if that makes any difference. I don't need a fully designed launching stage (I wouldn't be against it if someone wants to do that for me though ) but I could really do with some advice or new ideas on what I could possibly do just to get this up there, because It's got me completely stumped.

[James Kerman]

It sounds like you might be pushing the rocket too fast through the lower atmosphere.  I generally try to have my rockets moving at 250m/s at 10,000m. 

Ok so your launcher will need about 3500dv.  If you are set on playing stock you can use the Tsiolkovsky rocket equation or if you don't want to do the maths you can install this mod that will give you the figures in the VAB.

Also you could look in the spacecraft exchange for a lifter that can get 26 tons into orbit

Edited September 8, 2016 by James Kerman
Edited for more info

[DD_bwest]

how heavy is it?   id go tri-core design.  3.75m.  7 of the vectors bolted to the bottom. cross feed fuel to middle core. and finish it with a "smallish" rhino to help finish it off.  large fins.    

 

i find the tri core helps keep it stable

do you use any mods for extra data?

[zeanomourph]

12 minutes ago, James Kerman said:

It sounds like you might be pushing the rocket too fast through the lower atmosphere.  I generally try to have my rockets moving at 250m/s at 10,000m.

Ahk, I will give that a go, I'd heard not sure where that it's best to keep it under 350m/s til 10km so that's what I was mostly aiming for, but it definitely does seem less stable the faster it gets so that might be on the money.

8 minutes ago, DD_bwest said:

how heavy is it?   id go tri-core design.  3.75m.  7 of the vectors bolted to the bottom. cross feed fuel to middle core. and finish it with a "smallish" rhino to help finish it off.  large fins.    

 

i find the tri core helps keep it stable

do you use any mods for extra data?

Currently at ~25.5T with all tanks only half filled, . You've kind lost me a little there, how do I get 7 vectors mounted to a tri-core, and which is the middle tank with a tricore design? You mean crossfeed from outer tanks to all three of the middle ones, or crossfeed to a rhino transfer stage above the launching stage? Or a rhino center of the launching stage with 3 more cores mounted around it being the tri-core? Sorry, I am still pretty new to the game.. I've only been playing about a month so far and not quite up to scratch on all the lingo.

Not running any mods at all either, prefer to eyeball it or trial and error because I find it more fun that way, but if I can't get this one up tonight I might just cave and grab KER or find something on the spacecraft exchange as James suggested.

[DD_bwest]

by tri core i mean a design like the falcon heavy.   and the large vector engines can be placed on the bottom  of a 3.75 tank without using a node. so with 6 symetry you can strap 6 to the bottom, and then a 7th on the node.   if you put them on a small 3.75m tank, you can save it as like its 1 large engine.   the tri core would have 3 of these powerhouses,  and cross feed to the middle will give a small delta v boost

[zeanomourph]

Ok cheers, never knew you could mount vectors off the node, that's pretty cool.

For now I gotta head off to work (damn job getting in the way of my Kerbal time! lol) but I will give it a shot tonight as well as trying a slower launch as per James' suggestion, and I'll let you guys know how it goes.

Thanks for the help  

[HebaruSan]

2 hours ago, zeanomourph said:

Hey all, I know it's kinda frowned on asking people to help design a rocket because that's half the fun of the game..

On the contrary, some of us enjoy building lifters and see questions like yours as opportunities to have fun. Thanks!

I copied your payload the best I could (leaving the tanks full) and ended up with this; spoilered in case you prefer to try it on your own instead...

Spoiler

First stage is a central Mainsail crossfed by twin Skippers (similar to a "tri core" design), aided by 4 Thuds because the pad TWR was just slightly too low. Struts from the upper stage to the payload are important because docking ports and decouplers tend to be structural weak points, and this has two of them in a row. Luckily placing these struts was made easier by the bulging shape of the payload.

The side tanks drop when empty as usual. Fins at the back of the upper stage, combined with more larger fins at the back of the lower stage, provide stability through the whole flight.

When the Mainsail's tanks empty out, a Skipper-based upper stage takes over. It would be nice to use a "true" vacuum engine for this stage, but a Poodle would be too weak and a Rhino would be overkill for this payload.

This was an unusually efficient launch for me, as my periapsis was nearly positive before I even left the atmosphere.

I circularized at 80 km with a healthy margin of fuel to spare. It should be relatively simple to add enough delta v to get to 450 km; worst case scenario, you could transfer fuel from the payload to the upper.

 

[DD_bwest]

ya my suggestion would have been overkill for a load like that lol, but its a great design for much much heavier payload lol

[Norcalplanner]

3 hours ago, zeanomourph said:

Ahk, I will give that a go, I'd heard not sure where that it's best to keep it under 350m/s til 10km ...

This is old advice.  With the current aero in the game, you want to do a real gravity turn - go straight up until you're going somewhere between 20 and 50 m/s, then nudge it a little bit to the east (about 5 to 8 degrees).  Then lock your controls on prograde hold.  If you're having trouble flipping then add more fins to the bottom and/or put the whole payload in a fairing.  Don't worry about going too fast in atmosphere - ignore the flames, but pay attention to the temperature gauges when they pop up.

Regarding the lifter, a single Mainsail plus four Kickbacks should be plenty.  Here are pics of a cost-effective lifter I did which puts 41 tons into orbit.

Edited September 8, 2016 by Norcalplanner

[zeanomourph]

3 hours ago, DD_bwest said:

by tri core i mean a design like the falcon heavy.

Ohhhh lol things are pretty quiet at work today so I just googled the falcon heavy, that's very different to what I had in my head, I was picturing it using the tri-coupler to mount the three cores and like what where do you get a middle engine with that, and the tri-coupler only supports 1.25m tanks. All makes a hell of a lot more sense now.

1 hour ago, DD_bwest said:

ya my suggestion would have been overkill for a load like that lol, but its a great design for much much heavier payload lol

I was kind of thinking that, I tried it at some point with 4 vectors mounted on a quad-coupler and it was way overpowered and was running through fuel crazy fast too. I'll definitely keep it in mind for when my payloads start getting heavier and heavier, this is just the beginning

 

1 hour ago, HebaruSan said:

On the contrary, some of us enjoy building lifters and see questions like yours as opportunities to have fun. Thanks!

I copied your payload the best I could (leaving the tanks full) and ended up with this; spoilered in case you prefer to try it on your own instead...

  Reveal hidden contents

First stage is a central Mainsail crossfed by twin Skippers (similar to a "tri core" design), aided by 4 Thuds because the pad TWR was just slightly too low. Struts from the upper stage to the payload are important because docking ports and decouplers tend to be structural weak points, and this has two of them in a row. Luckily placing these struts was made easier by the bulging shape of the payload.

The side tanks drop when empty as usual. Fins at the back of the upper stage, combined with more larger fins at the back of the lower stage, provide stability through the whole flight.

When the Mainsail's tanks empty out, a Skipper-based upper stage takes over. It would be nice to use a "true" vacuum engine for this stage, but a Poodle would be too weak and a Rhino would be overkill for this payload.

This was an unusually efficient launch for me, as my periapsis was nearly positive before I even left the atmosphere.

I circularized at 80 km with a healthy margin of fuel to spare. It should be relatively simple to add enough delta v to get to 450 km; worst case scenario, you could transfer fuel from the payload to the upper.

 

Glad to provide the opportunity then  hah I think it was a reddit page I found through google I saw someone had asked for help designing their rocket and got ripped up by people saying something along the lines of 'figure it out yourself ya lazy bum that's the whole point of the game' lol.

That's an awesome design, thankyou! I did try something similar but still very different, and it was probably the closest I got all night (5x 1.25 tanks/swivels instead of 3 orange tanks with bigger engines, after decoupling the first set of boosters it looked just like a much smaller version of that.. but after decoupling the second set leaving only the middle tank with 1 swivel still only maybe 30km up I guess it was just too top-heavy and that's when that one started flipping) (edit: come to think of it I think that design MAY have been for a different module I launched before this one.. would 5 swivels even get this off the ground?). But I ended up scrapping it because everything I tried was just failing so horribly, instead of attempting to refine any of them I just completely remade the whole launcher with a totally different concept every time.

Including proof of launch, and with a full fuel load and everything! Thank you for that, I will most likely just completely copy that design tonight and see if I can make it work. I realised after posting this topic, and it totally skipped my mind last night, but the whole time I was doing it with no SAS as well, there's no control module and was trying to launch it with an engineer so I don't need to send another ship up to bring back one of the few pilots I have left.. massive facepalm on that one now I think of it I'm sure at least one of my attempts would have worked if I had even basic stability control  derp lol.

Edited September 8, 2016 by zeanomourph

[Harry Rhodan]

Dat aliasing ...

 

The key usually is to have your main stage running well above the 10km mark. This thing keeps going to 30-40km before staging to the upper stage. At that point you don't need additional fins on the upper stage.

[Plusck]

7 hours ago, zeanomourph said:

...I've already dumped half the fuel out of every tank on it because I can refill them once I get it connected to the station...

This actually might be the cause of all your problems.

The lighter the top of the rocket, the less stable it is. Leaving all the fuel in the payload raises the CoM (especially in the crucial phase when the first stage's uppermost fuel tanks are empty, but aero forces are strongest), so that torque from the draggy payload doesn't have a long lever arm to work on.

If that still doesn't work, even if you stick perfectly prograde all the way, you can also accept the inevitable costs and simply add more drag to the bottom of the lifter: bigger fins obviously, but less obviously not staging your SRBs or even adding a quartet of small, unstreamlined SRBs at the bottom just to add drag until you get to a safe altitude.

[zeanomourph]

Thank you to everyone for your valuable inputs, I definitely feel like I've learned a lot today.

In the end I went with @HebaruSan's design just because it was already there, nice and easy.. it still got a bit wobbly on me especially with the SAS on prograde hold it would get pretty out of control, so I had to baby it all the way up there but it worked a charm, twice. (side question- does anyone else have problems with quicksaves? I got a 0.0km intercept node but then overburnt ever so slightly up to 0.7km, figured I can do better than that so I quickloaded and it bumped me back to a save from last night and I had to roll out to the pad again  not the first time it's happened either).

Second attempt got the transfer burn perfecto and had the actual intercept at 0.0km even after closing the node, right on the target apoapsis.. super happy with that, best I'd done before that is 0.2km after the burn.

What a beautiful thing! But wow trying to dock that thing controlling it from a port on the side of the module was interesting lol, second hardest docking maneuver I've done. First was using the little construction probe you can see on the mid-right side to catch and connect the solar panel module which has no control of it's own... so unbalanced lmao.

It's not much compared to some of the epic stations I've seen pics of, but I'm pretty happy with it so far, first station I've even attempted in the 4-5 weeks since I bought the game... and it all started from that tiny little science probe on top of the research bay, first thing I sent into space with a docking port on it haha.

Thanks again for all the advice and information, I took the easy route on this one but I have no doubt it will help a lot for future launches.

[Sharpy]

Well, if you don't need all that fuel in orbit, you can significantly reduce the complexity of the launcher.

Here, 70km orbit with 255m/s left, in 6 parts.

Docking port has staging and crossfeed enabled. Twin Boar has gimbal limit 20.x

Flying instruction: Immediately after take-off, tilt to 80 degrees west and keep it there. Switch SAS on, set it to prograde and let go of everything once the prograde marker catches up with center of navball. Switch engines off when apoapsis is over 70km, then perform circularization.

If you need more delta-V to reach the target, replace the tank with orange one, and begin gravity turn a little bit more shallow.

Of course if you need *all* that fuel... but then you're better off launching a dedicated fuel delivery in a less unwieldy package. Or just catch an asteroid

 

[zeanomourph]

9 hours ago, Sharpy said:

Well, if you don't need all that fuel in orbit....

Hah yeah, TBH I really didn't need any of the fuel in orbit as of launch, I'm just kinda prepping the station for use as a kind of orbital gas station for future missions that I haven't even planned yet, so I can launch bigger landing vehicles with lighter/no fuel payloads and just fill them up once in orbit. I've already got fuel delivery systems designed to refill as it's needed (similar to the 2 pods connected at the bottom of the research module, but a bit bigger because those are LF only to run the NERV). Launching them to refill it once in orbit was the original idea when I half emptied the tanks to lower weight on this launch, but Hebaru's launch vehicle got it up there fully loaded so that saves me an extra launch or two

It's probably still not as efficient as just getting my launch windows right and sending the missions straight where they're meant to go, but that's difficult with no mods and hey I'm having fun so that's what matters

Thanks for the idea though I hadn't even thought of the twinboar. There's a lot I didn't think of lol as I mentioned it was my first time launching something this heavy (even half empty it was still roughly twice the weight of my previous heaviest payload), and most of the rockets I was trying were either too small, or got frustrated at the "small" ones not working and just skipped over reasonable size straight to absurdly big.

I think my major problem was that I was thinking along completely the wrong lines, that my failures were more due to the shape and weight of the payload than my actual rocket designs, because I can get most of my lighter and more aerodynamic payloads into orbit first go almost every time now. Definitely learned a lot from this experience, and from you guys.

[Jarin]

19 hours ago, zeanomourph said:

First was using the little construction probe you can see on the mid-right side to catch and connect the solar panel module which has no control of it's own... so unbalanced lmao.

I'm impressed you managed that at all without any mods. I rate Docking Port Alignment Indicator as my second most important mod, after KER. I figure, real space programs don't have to dock by Mk. 1 eyeball and the seat of their pants, so why should I?