Best way to get an orange fuel can in space w/o using its fuel?

[Hour Hero Yes]

I'm in the middle of adding fuel tanks to my space station for refueling, and I always struggle with making an efficient launcher for getting orange cans off the ground. They get very top heavy, or long and wobbly, or just hugely inefficient. I also like to try to be as minimalistic as possible, for practice when money and resources actually become an issue in the game.

My current design is this. It gets to orbit and eventually gets to my station, but it's really inefficient and a horrible klutzy thing to adjust in space for pre-docking maneuvers.

I assume this is a pretty common maneuver, so I'm just wondering if anyone has favorite fuel-launcher designs!

[austin4050]

Mainly I just have spare fuel and divert it into the orange tank, it may take several trips however it does work.

[Hour Hero Yes]

I'm a somewhat impatient sort, so I like to try to save it all to get into space

My current design DOES get a completely untouched orange tank up there, I'm just not sold on the launcher.

[allmhuran]

The large RCS tank actually weighs quite a bit (4.5 units IIRC?) which will be hurting your rocket's performance more than you might think, and you certainly don't need all that RCS just for this rocket.

[Hour Hero Yes]

The large RCS tank actually weighs quite a bit (4.5 units IIRC?) which will be hurting your rocket's performance more than you might think, and you certainly don't need all that RCS just for this rocket.

Ah good point, I should have mentioned...I included the RCS tank for monopro refueling needs at the station as well. A one stop shop, if you will.

[austin4050]

although rcs is not really needed for orbit achivement, maybe just a tad-bit. I would suggest taking off RCS unless the station is orbiting another planet.

[SkyRender]

As you clearly surmised, that is a very over-designed launcher. Here's a much simpler one that will get the job done.

Its design uses asparagus staging to get the most out of fuel efficiency, and plenty of struts to keep things stable. It also features power generation and a spare battery, just because it can. It has around 4400dV in the launch stage, more than enough to get it to orbit. In fact, that's enough to get it halfway to the Mun... If you really want monopropellant, just jam 4 large side-mounted RCS tanks on the side of the fuel tank.

EDIT: Here's the .craft file, if you want to see for yourself. I took the liberty of adding 4 large-size monopropellant side tanks to it, so it has 600 RCS now too (at the cost of about 100dV; 4300 is still more than enough to get to orbit). Also, there's no RCS ports on it, so if you don't feel comfortable docking without it, you may want to add a few...

Edited August 2, 2013 by SkyRender

[dlmarti]

https://www.dropbox.com/s/uovsk0a8jazgcqt/Fueler%20Mk6.craft

Jumbo 64 in orbit, with RCS and engines, with another 1/2 Jumbo + engine to help get it to where it needs to be.

Look at the way it is struted, this makes the entire thing ultra stable.

Edited August 2, 2013 by dlmarti

[Duxwing]

I put plenty of Sepratrons atop the orange tank and then put it directly (no decoupler; you'll see why) atop a core lifter that has a three meter RCS tank, four RCS blocks at its top and bottom, and two fixed solar panels that has six Mainsail motors in asparagus staging around it. Two orange tanks are above every motor, and a strut connects the top of each radial engine to the payload tank; I bind the '1' key to an action group that locks the gimbals of the radial engines and strut them to the core engine so that the lifter stays together, and I keep the whole rocket in place with radial launch clamps attached to the radial engines at the level of the center of mass and engage the action group before launch. The design flies smoothly, has plenty of fuel and maneuverability at high and orbital altitudes, and its Sepratron motors can deorbit the craft after all the tanks (lifter tanks included--use their fuel to refuel craft as well) out of fuel.

Be sure to disable fuel flow from the payload tank if you absolutely must have it reach orbit untouched--tapping into it is unlikely, but better to revert to launch lower than higher

-Duxwing

[nimbim]

First a general tip for your rocket designs: Winglets need to be near your thrusters, the sets you have installed in the mid- and top-section actually make your rocket less controllable.

An easier to fly design could rely on a smaller last stage, i.e. just 1 orange tank with a Mainsail. Use 2 orange tanks stacked as boosters, that will give you a longer, consistent burn to get most of the way into orbit. Disable gimbal on everything except the center Mainsail that you use the entire time. And struts.

[aNewHope]

This one is pretty efficent and can get a full Jumbo Tank to Minimus and beyond (with some luck maybe to Duna/Eve).

[Hour Hero Yes]

Awesome tips, thanks everyone. I didn't know that about winglets being near the actual engine.

[BigDog]

Why send just 1 orange tank when you can send 8!

It might just be the way I design things, but I find once I get past a very simple rocket having winglets at the top and bottom works best.

[Captain Sierra]

This rocket seems overdesigned. I was planning on releasing my Nova launcher family which can orbit an SSI fuel can (similar in design) with ease. Suggestion: Less center stage, more boosters. Also don't forget you need a docking stage to dock it and then preferably deorbit itself.

[Hour Hero Yes]

Suggestion: Less center stage, more boosters. Also don't forget you need a docking stage to dock it and then preferably deorbit itself.

Definitely going to take a look at the center stage. The top and bottom of the orange can/RCS section are Sr. Docking ports.

[Captain Sierra]

no, I mean a small final stage that has a probe body and RCS thrusters to dock the fuel tanker to the target station/ship/base/whatever or else you will have to orbit it then have a tug rendezvous with it and take the fuel tank back. EDIT: I may post a pic of the Nova II which is what I use for just this. It has the thrust to put anything under 50 tons into at least a 150km orbit and still rendezvous and dock the payload. It's how I build space stations and deliver my fuel tankers.

[arq]

Look into asparagus or onion staging (I use onion, which is slightly less efficient but much easier to build) if you want to put heavy things into space. Actually I would recommend Kerbal Engineer Redux or Mechjeb to get the readouts of TWR and delta-V if you want to go about building efficient launchers. You want a TWR around 1.7-2.2 (lower is okay in the last stage) and about 4500dV to get to orbit. So if you can design a launcher with those stats and whatever payload you want on top (not counted in the 4500), it should get it to LKO.

One of the above posters suggested that 4400dV would get you halfway to Mun. The user is likely using FAR, which changes aerodynamics dramatically and reduces dV to LKO. In stock 4400dV is just barely enough to get to LKO. A carefully designed and flown launcher could maybe do it for 4200, but likely no less, and most require 4400-4600.

[SkyRender]

One of the above posters suggested that 4400dV would get you halfway to Mun. The user is likely using FAR, which changes aerodynamics dramatically and reduces dV to LKO. In stock 4400dV is just barely enough to get to LKO. A carefully designed and flown launcher could maybe do it for 4200, but likely no less, and most require 4400-4600.

Actually, that 4400dV is at sea level. The vacuum dV is closer to 5000.

[Kerbonautical]

Another little tip. Get that huge RCS fuel tank off the top and replace it with a couple of radials placed further down instead. It will be easier to control and you will shed some weight overall and more importantly from the very top of the rocket. Personally I've found it's a lot easier to send up a larger RCS fuel supply with a lighter part like the payload and then exchange it back and forth between between the vessels sections as needed. Plus even 4 small radials will supply you with enough RCS to perform at least two docking maneuvers.

[antbin]

I didn't know that about winglets being near the actual engine.

Not so much "near the engine" as "near the back of the rocket". Anything that steers generally works better at the back. Things that don't steer (like non-gimbaling rockets: LV-T30, aerospike) it doesn't matter where they are.

[TinfoilChef]

A while before the great crash of 4-13 I saw a thread with a challenge to lift a full jumbo 64 fuel tank to orbit. This was my entry.

X-Ddrive mk2 (STOCK) craft file: http://pastebin.com/rPaKChAC

Video of the proof flight:

It can reliably deliver a full Jumbo-64 and a full FL-R1 to an 80 - 150 km orbit. (or the 60 ton payload of your choice if you replace the jumbo 64) along with a crew of two kerbals.

I continued using it not only to deliver fuel to orbit but also as an interplanetary transfer stage. The launch stage has proven useful for lifting heavy payloads in general.

Later I modified it some, adding solar panels, batteries, a second docking port for chaining multiple ships together, forward and aft facing lights for docking, Aviation Lights and Quantum Struts.

Importing it to 0.21 I added reaction wheel units (possibly too many, I don't yet know how much force is needed per ton of ship).

XDD mk6 (Modded) craft file: http://pastebin.com/9vuEcvRb

[Vanamonde]

This http://forum.kerbalspaceprogram.com/showthread.php/25779-Orbital-refuelling-tanker is a robotic refueling tanker that can deliver an orange tank to a ~300km orbit without calling upon the fuel in the tank itself.