Refueler

[lumpman2]

I've tried several times to make a rocket that can refuel my interplanetary lander, but my designs so far have been unable to go past ~60 km and reach a stable 100 km orbit to dock with my lander. It also does barrel rolls when I start tilting east around the 10 km mark. Here's my last design:

Anyone have any good designs for a refueler? I need something that can fill a large tank and a quarter if I remember correctly.

[Key of door]

Try adding more asas.

[7rex]

For top heavy rockets like yours you'll need to turn later once the air has thinned right out. Also, add SAS wheels, they will help.

[ThePsuedoMonkey]

You have a lot of thrust in your first stage; if you add four large tanks to it you'll still have a TWR around 1.9 and could bring that tank into orbit almost untouched. If you also asparagus them you can take it up completely full.

[rpayne88]

You can try strapping some SRBs to the first stage (make sure they burn out and drop before your liquid boosters, though.) This will allow you to leave the pad with a much lower throttle setting than with out them. This means that when you begin your gravity turn, you have more weight towards the tail o your rocket, helping to keep it stable.

Note: this works for me but I do use FAR.

Edit: As for the "barrel rolls," are all your struts on straight? Misaligned struts have been know to cause phantom torque on rockets.

[Vanamonde]

You could try this one: http://forum.kerbalspaceprogram.com/showthread.php/25779-Orbital-refuelling-tanker

[lammatt]

why would someone want to deliver a stock rockmaxx tank when he can deliver a full 5 X 6 tank with ease...

i mean... why else do we have nova punch for?

a lifter with the 5m 7500kN lifter engine on a 5X9 tank and then surrounded by four 3.75X9 with the 2600kN engine in asparagus can take the payload to orbit already...

it's 53 parts in total and able to deliver a ~70-80% full 5X6 tank to ~100km

why need a 100000000000000000parts stock rocket to do the same easy task?

Edited August 6, 2013 by lammatt

[Johnno]

why would someone want to deliver a stock rockmaxx tank when he can deliver a full 5 X 6 tank with ease...

i mean... why else do we have nova punch for?

Because someone doesn't want to use mods? Or specifically 'easy mode' mods?

Why 'we have' the nova punch mod? Because it was made. There's hundreds of mods, do you have every single one installed?

[shand]

Try putting the fins on the central stack - i imagine the problem you are having is the outter tanks stage off, leaving the inner stack with no aerodynamic assistance. also swap out the outter stacks to skippers if you can, more fuel efficent.

[lumpman2]

You can try strapping some SRBs to the first stage (make sure they burn out and drop before your liquid boosters, though.) This will allow you to leave the pad with a much lower throttle setting than with out them. This means that when you begin your gravity turn, you have more weight towards the tail o your rocket, helping to keep it stable.

Note: this works for me but I do use FAR.

Edit: As for the "barrel rolls," are all your struts on straight? Misaligned struts have been know to cause phantom torque on rockets.

I was thinking it could be the struts, but I'll try that.

[Rondon]

well I rebuilt your refueler based on the picture and I would say that that your design has too much thrust to weight in the first stage, this could be solved by adding an additional stage in between, the final and second stage although you'd probably need struts for that, or you could change the four mainsail engines to skipper engines, but even then I was short 500 delta-v and the atomic engine just cant get manage that in three minutes you have,(although maybe you fly in a different way than I do, that could get the time). after redesigning it I could get a 1 and 1/7th jumbo tanks worth of fuel up to 100km

heres my redesign

As for the barrel roll, dunno the design didn't create any problems like that, probably just need to find the right combination of wings and RCS.

[AnalogAddict]

Add some sets of SRB's to that booster stage from the images, that should give you the extra oomph that you need to get to orbit.

My refueler looks dangerously similar to these. I use Mainsails on the 6 outer boosters, and the new Skipper on the center stage. No fuel lines and the Skipper only fires after the initial booster stage is jettisoned. That usually gets to orbit with more fuel than the one orange tank can hold, I end up piloting an unwieldy rocket with its upper stage still attached.

[Blue]

My mainstay refueler is actually quite similar, though I daresay 'cleaned up' a bit.

The bottom stages are asparagus-- Engines 1 and 3 jettison at around 3800m, Engines 2 and 4 at about 20000m, and the Core stage can get me all the way into orbit as high as 200km without cutting into the payload.

The entire length from bottom to top are struts to keep vertical integrity, since right before the final asparagus staging the seperator for the payload takes some serious Gs and has buckled frequently in the past.

All in all, the launcher I call "Clover", and is a useful all-purpose heavy lifter for anything under 60 tons.

[Xiphos]

If you take what you have in your center stage, and copy that for a 6 stage asparagus rocket you will get that into a 100km orbit with plenty of fuel to spare. Also anything you can do to make the rocket 'shorter' will help. ie: that LV-N really isn't necessary because for the power/weight you can swap it out for something more suited for the task of just docking. You want to be able to do strong, powerful burns to cancel your velocity to match a ship instead of a really long, drawn out burn. And as far as the rotation, add more struts going around your outer booster stages. I think that should help.

Edited August 6, 2013 by Xiphos

[lumpman2]

Ok, thank you all for your suggestions. I put them all into my design and with a bunch of trial and error, I managed to get into a fairly large sub-orbital trajectory. However, the mainsail runs out right after it reaches 100 km (at least I got there) and it takes an immense amount of thrust on the nuclear engine to even see my periapsis. Then, when I gave up trying to expand anymore, the atmosphere caught me and pulled it straight down to the ground. What kinds of engines should I use to keep a large amount of fuel, but still reach my lander easily? I don't want to go sticking engines on there because I need to save as much fuel as possible for when I get to the lander.

[Anton P. Nym]

However, the mainsail runs out right after it reaches 100 km (at least I got there) and it takes an immense amount of thrust on the nuclear engine to even see my periapsis.

That's the LV-N's greatest problem; thrust to weight is dismal, so bad it's just unsuited for circularising in LKO. I'd recommend replacing that with a Skipper, whose lower I(sp) is more than made up for by its vastly higher TWR. (If you're absolutely wedded to having a high-I(sp) engine there, the aerospike is a bit better than the LV-N in this case.) No, forget that bit; just remembered you can't put a stack separator on an aerospike, so that'd require a complete overhaul of your launcher's design.)

LV-Ns are great for getting to other worlds, but can't cut the mustard when just poking around Kerbal orbit.

-- Steve

Edited August 6, 2013 by Anton P. Nym
On second thought...

[Tokay Gris]

I use this one:

The Orbital Tanker "Lumox", in this configuration unmanned.

It can lift 2 Jumbotanks into orbit (Kerbin orbit, with fuel to spare, so higher orbits are no problem), can rendezvous with a vessel, usually has RCS-fuel left and has enough electricity to not run out.

Craft-File is here:

ftp://[email protected]/Craftfiles/OT%20_Lumox_%20MK%203%20raw.craft

Just rightclick and "save as" or "Download linked file as..." if you are on a Mac.

I think I unplugged MechJeb in the craft-file.

I did use this one to excess in the "Glory Road"-mission.

[lumpman2]

I managed to get into orbit - thank you everyone for your suggestions! I replaced the atomic rocket with a skipper and it now can easily acheive a stable orbit, at the cost of burning a bit more fuel.

Now, the problem I have is docking. I had absolutely no clue on how to get close to my target. I ended up burning a ludicrous amount of fuel and got an escape orbit from Kerbin, and then I decided to burn straight towards the lander, but I ran out of fuel and had to revert. I'm not exactly sure how to do this and I have read a tutorial, but I have no idea how to do it efficiently without wasting all the fuel that i'll be using for refueling.

[JohnDoe]

I launch right when the target is over the Space Port and go in a 73km orbit. Then you are behind your target and move on a faster orbit. You just have to do a Hohmann transfer at the right time to get your rendevouz. For the last kilometers i first kill relative vel. than head towards the target. Repeat until youre about 30-50m apart. Then dock.

[Tripzter]

Add more orange. 7 rockets does it for me and usualy the center one is left with 60-70% fuel by the time i'm in good orbit.

This is my space station refueler. The 6 tanks around drop off during launch. The last bottom orange tank gets me 1-2k to my station with fuel to spare, i jettison it to make docking easier, then i use the nuclear engine+rcs thrusters to dock it. At last once i'm docked you see the clamp on the bottom between the remote guidance module and the large orange tank on top? I disconnect from there and leave the orange tank attached on the station and plummet the rest into the planet. (The orange tank on top that leave at the station remains at 100% fuel)

Edited August 6, 2013 by Tripzter

[Corrupt]

Quick question to save a whole new thread. Once I have two craft docked, how do I feed fuel from one to the other?

[lumpman2]

Quick question to save a whole new thread. Once I have two craft docked, how do I feed fuel from one to the other?

Right click one of the fuel tanks, and then alt+right click the other fuel tank, and click "In" on the tank that you want to fill up. You can do this with any two tanks, but they must be the same fuel type and remember that you need to transport the oxidizer in addition to liquid fuel.