Problem with Asparagus Staging/Question regarding interplanetary tugs

[condraj2]

First off, I'm having trouble configuring asparagus staging correctly. I'm not sure what I'm doing wrong.. I understand the basic principle, attach radial engines in pairs around the main engine and connect them together with the last engine in the chain being connected to the center engine and then break them off working outside in. What I don't understand, however, is why it seems to work upon liftoff (all engines fire and all tanks stay full aside from the furthest ones along the chain), and then after I detach those, the center engine burns out completely and then stops while the outer engines, which are attached via fuel line, keep burning. As a result, the center isn't lifting while the sides are. I'm obviously doing something wrong, but I can't figure it out. I've also had similar situations where everything works perfectly until the first pair are ejected and then the center engine AND the last outer pair begin burning fuel.

What am I doing wrong!?

In regard to my second question, I've gotten to the Mun/Minmus back and forth and earlier today completed my landing (manned) on Duna using a one-manned capsule and an interplanetary nuclear tug (with 1 NERVA). Obviously, the burn took forever and while I eventually got there, I've used up a lot of fuel and probably won't have enough to get back (assuming I need roughly the same amount, which may or may not be accurate). My question is: what is the most efficient engine configuration for interplanetary NERVA tugs? Is one NERVA really the way to go or are two or three? For the record, I'm not using any mods, so I'm sure that plays into things a bit in terms of accuracy/wasting fuel.

Thanks in advance!

[zanzibar196]

Sounds like you got a fuel line or lines in there going backwards... pulling from the center tank to the outside ones... pay attention to which way the arrows on your fuel lines are going...

[stupid_chris]

For the fuel lines, there's two things: One, you might've, indeed, routed fuel in the wrong way. Double check your lines to be sure. Second, you might've created a fuel loop and the game hates those. A screenshot of the craft in question would greatly help.

Second, you are getting to the core of the tyranny of the rocket equation. If you add another LV-N (NERVA) To your craft, you will have a higher acceleration, but you will also be carrying more weight, meaning less delta V. It's a trade off of TWR for delta V, you have to choose what you can afford really.

And coming back doesn't take more fuel by the way If you consider that you will come back straight to reenter Kerbin, the only fuel you will expend is the one to achieve Duna's escape velocity, which is much lower than Kerbin's, and the orbital adjustments. Basically, as much fuel as it took you to circularize your orbit if you didn't aerobrake.

[Cheebsta]

This doesn't work 100% of the time, but it is a useful trick:

Place your first radial tank. Flip your view around until you can see through the main tank to the side of the radial tank facing it. Use the decoupler to estimate where the tank center is, and place the fuel line as close as you can to that, about a decoupler length below the decoupler. Spin your view around the other way, and do the same for the other end of the line into the main tank. Now just hold Alt and pick up the radial tank *at the decoupler*. When you place the next tank the fuel line should already be there. The decouplers should stage properly without you having to fool with them too.

Also works with struts, but be careful, I am fairly certain using it on them has caused spontaneously dis-assembly on a couple of my rockets.

[HoY]

To simplify the build you can watch the second video in my signature. I know you already know how to build asparagus but just in case

[Cheebsta]

To simplify the build you can watch the second video in my signature. I know you already know how to build asparagus but just in case

Not sure you actually meant me, but I did this, and I think my way is actually simpler... Though maybe not "asparagus"? I am not sure what defines that.

I only set up 1 tank, with engine, decoupler, and fuel line the way I said above. 2-3x symmetry. Dupe the tank assembly, and stick it to the side of the tank I just duped. You can add a ton of tanks this way if you want... doesn't really do anything, but is fun to set off 25 mainsails at once.... And for some reason it doesn't take half the struts sticking them to the main tank, or in rings, does. Fuel lines add themselves (apart from occasionally sticking to the end of themselves for some reason), and you just have to move engines to the bottom stage, or wait to add them till the tanks are on.

[stupid_chris]

Not sure you actually meant me, but I did this, and I think my way is actually simpler... Though maybe not "asparagus"? I am not sure what defines that.

I only set up 1 tank, with engine, decoupler, and fuel line the way I said above. 2-3x symmetry. Dupe the tank assembly, and stick it to the side of the tank I just duped. You can add a ton of tanks this way if you want... doesn't really do anything, but is fun to set off 25 mainsails at once.... And for some reason it doesn't take half the struts sticking them to the main tank, or in rings, does. Fuel lines add themselves (apart from occasionally sticking to the end of themselves for some reason), and you just have to move engines to the bottom stage, or wait to add them till the tanks are on.

You mean you're dropping all the tanks at the same time? That means you're not really doing Asparagus, more like simple fuel crossfeed, or onion staging as some people like to call it.

[Cheebsta]

You mean you're dropping all the tanks at the same time? That means you're not really doing Asparagus, more like simple fuel crossfeed, or onion staging as some people like to call it.

No, no, they drop 2-3 at a time, depending which symmetry I use to put them on. I just only have to place 1 fuel line, 1 tank, 1 decoupler, and 1 engine (with symmetry of course). Only the first set of radial tanks is actually connected to the main tank via decoupler, and the fuel lines get duplicated with the tanks and attach themselves to the previous tank, so long as they are placed near that center line.

Edit:

Like this, where blue line is decoupler with fuel line directly under it.

Edited July 20, 2013 by Cheebsta

[stupid_chris]

Hmm, that is asparagus indeed, but that honestly smells like a lot of wobble and structural instability to me. But heh I bet it works, that's the important part.

[FleetAdmiralJ]

There are two things that always bite me when doing asparagus:

1) make sure that when you're adding fuel lines, you're doing it for both sides (or if you add tanks in, say, a group of six, that you link the fuel pods together correctly one-by-one), and

2) make sure you are connecting the fuel lines in the right order. Fuel always runs from the tank you start the fuel line from to the tank you connect to. If you connected the line from the center tank to the last asparagus stage, then the fuel will be running the wrong way.

Edit:

Fuel lines add themselves (apart from occasionally sticking to the end of themselves for some reason)

Do you mean you're alt-clicking the tanks to copy them, pasting them next in line and letting the fuel lines attach where they may? that could be part of the problem...

Edited July 20, 2013 by FleetAdmiralJ

[Cheebsta]

The exact design in the pic would be a little hairy because of stage 5, I was just whipping up general concept in 30 seconds in Paint without putting much thought into function. You wouldn't want that stage stuck between the next and main like that because you'll likely be in gravity turn when it goes, and it's probably not going to come out of that hole without taking something else with it, likely an engine, which equals disaster pretty quick.

It really should be a giant disaster... I built the first one just screwing around... and it flew brilliantly. Been using it ever since for heavy rockets.

[Cheebsta]

Do you mean you're alt-clicking the tanks to copy them, pasting them next in line and letting the fuel lines attach where they may? that could be part of the problem...

The trick is what I said about lining them up on center using the decoupler as a guide. This makes sure that when the duped line goes looking for an attachment point it looks in the same direction the decoupler is, which sort of has to be the tank you attach to, and if you always attach the next tank to the previous tank they stay in order.

The exception is when the fuel line doesn't connect to anything and ends up just a nub on the side of a tank. I am not sure why this happens, but once in a while it does.

[FleetAdmiralJ]

The trick is what I said about lining them up on center using the decoupler as a guide. This makes sure that when the duped line goes looking for an attachment point it looks in the same direction the decoupler is, which sort of has to be the tank you attach to, and if you always attach the next tank to the previous tank they stay in order.

The exception is when the fuel line doesn't connect to anything and ends up just a nub on the side of a tank. I am not sure why this happens, but once in a while it does.

I wouldn't assume that (though I suppose one could build a rocket in that way, but I would think it would be extremely unstable). When I do an asparagus of 6 orange engines outside a center orange engine, all 6 of those engines are attached to the center, but only two of their fuel lines attach to the center.

[Cheebsta]

It doesn't work because it's logically or realistically stable. It works because this is a video game.

[Torch]

I think it's all been said, but I'll add my 2 cents anyway, and tell you how I do it. I think the previous posts where correct, if your center stage is running out before the "asparagus" bits, then you probably have a fuel line running from the center to the last stage in your asparagus, as opposed to from the last stage TO the center. Anywho, to help that, here is how I do it. Lets say I want a center large fuel tank with 6 radial large fuel tanks. For the first radial tank, I add the decoupler, tank, engine, and struts with 2x symmetry. I don't add fuel lines as they have to run from the tank you just placed (with 2x symmetry) to the tank you are ABOUT to place, which doesn't exist yet! I then dupe the first tank at the decoupler and place it next to the first tank. This gets the decoupler, tank, engine, and any struts I placed. I do this a third time to get all six radial tanks. To place the fuel lines, since you used 2x symmetry vice say 4 or 6x, when you connect the first placed tand to the second, 2x symmetry will automatically be applied. Do the same for tank 2. For tank 3, which is where I think you went afoul, make sure the line runs from the third tank, to the center tank, and all should be welll An added benefit to this method is that your staging should reflect your 2x symmetry, ie, you should be able to move the respective decouplers in short order to the correct staging location. hope this helps!

[Cheebsta]

View from inside main tank, fuel line is there, but obscured by the lines built onto the tank coming down.

Connecting to main tank:

Symmetry added, everything from here is just duping (except the cone and control bits):

Ready for launch, whopping total of 12 struts:

~7000m, and I still haven't pushed a button besides spacebar:

Finally here it starts to wobble, but again, not a single input from me other than spacebar. It rolls back and forth a little, but doesn't complete a full rotation till in around this mark either.

I placed only 1 fuel line myself in this build.

I did have to set the staging for the decouplers though.... Somehow I had it doing that itself too at one point... Just not sure now how.

[condraj2]

Thanks guys.. in the few minutes I had between when I created this thread and when it was actually posted, I figured out the asparagus issue. I was indeed ignoring the direction of the arrows on the fuel lines. Subtle changes made a huge difference. I experimented a bit with more nuclear engines and managed to get to Duna and back with relative ease once I settled on a configuration that I liked. Thanks for the help!

[Max Grant]

Thanks guys.. in the few minutes I had between when I created this thread and when it was actually posted, I figured out the asparagus issue. I was indeed ignoring the direction of the arrows on the fuel lines

I get burned (literally) by that one too, but I have an excuse: I need bifocals.