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herbal space program

Can't asparagus anymore -- what gives?

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Hello everybody,

So I spent a couple of hours yesterday building an asparagus-staged lifter for the Jeb's Junkyard challenge. When I launched it, I discovered to my dismay that all of the engines were able to reach all of the fuel equally and that each of my bundled stacks ran out of fuel at the same moment, no matter how I placed my fuel lines. Turning off crossfeed at the decouplers did not help. I then noted that there were now new right-click options for fuel management, and when I turned on the flow overlay I saw that fuel was flowing every which way, even though AFAICT the adjacent tanks were only connected via one-way fuel lines. So far, my fiddling blindly with these and my searches through this forum and the Wiki for an explanation of how all this works have been fruitless. Could somebody please point me to one if it exists?

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23 minutes ago, herbal space program said:

So I spent a couple of hours yesterday building an asparagus-staged lifter for the Jeb's Junkyard challenge. When I launched it, I discovered to my dismay that all of the engines were able to reach all of the fuel equally and that each of my bundled stacks ran out of fuel at the same moment, no matter how I placed my fuel lines.

Screenshot please?  Hard to diagnose what you're doing wrong when we can't see what you're doing:wink:

I can tell you that asparagus works just fine.  Always has, and still does in 1.3; I use it from time to time.  The only changes I've noticed lately are that the new fuel-flow options actually make it easier to build asparagus, in some ways (it's possible to make a functioning asparagus-staged vehicle without any fuel ducts at all, just using crossflow-enabled decouplers and setting the tanks' fuel flow priorities).

In any case:  yes, asparagus works just fine, so if you're having problems, either there's some devil in the details of how you've built your ship, or else (less likely) there might be some mod that's getting in the way.  A screenshot of your ship, showing how it's put together, would really help to diagnose whatever it is that you're (presumably) doing wrong.

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1 hour ago, Snark said:

The only changes I've noticed lately are that the new fuel-flow options actually make it easier to build asparagus, in some ways (it's possible to make a functioning asparagus-staged vehicle without any fuel ducts at all, just using crossflow-enabled decouplers and setting the tanks' fuel flow priorities).

^this.

The only thing missing is the hint that it's time to ditch the booster (engines stops). You need to open the part info window to see when the tank is empty. 

If the challenge allow it (I know it's unlikely) Smart Part mod have the Drainex that trigger a staging even when you reach a previoly set % of fuel in the tank.

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2 hours ago, Snark said:

Screenshot please?  Hard to diagnose what you're doing wrong when we can't see what you're doing:wink:

I can tell you that asparagus works just fine.  Always has, and still does in 1.3; I use it from time to time.  The only changes I've noticed lately are that the new fuel-flow options actually make it easier to build asparagus, in some ways (it's possible to make a functioning asparagus-staged vehicle without any fuel ducts at all, just using crossflow-enabled decouplers and setting the tanks' fuel flow priorities).

In any case:  yes, asparagus works just fine, so if you're having problems, either there's some devil in the details of how you've built your ship, or else (less likely) there might be some mod that's getting in the way.  A screenshot of your ship, showing how it's put together, would really help to diagnose whatever it is that you're (presumably) doing wrong.

 

Asparagus may still work fine, but it sure as heck doesn't work the same way it used to!  :/ I have done it exactly as I did it this time about a thousand times, going all the way back to 0.19, without any problems, and now that doesn't work anymore. Anyway, here's a screenshot:

https://imgur.com/a/XoepB

There are three side boosters connected to the central stack by a chain of radial decouplers, with a chain of fuel ducts going from the far stack to the center. It used to be that the outermost tanks would empty first in this configuration and then those engines would stop, with everything else still full. Now everything just keeps running until all the connected stacks are empty, as if the fuel ducts are not one-way anymore. As I said before, disabling crossfeed on those couplers made no difference. Anyway, I was mostly just hoping for somebody to point me to a tutorial on how to set tank priorities for asparagus staging, because there appears to be no detailed explanation of this new system anywhere on this forum, KSPedia, or the Wiki.

 

53 minutes ago, Spricigo said:

^this.

The only thing missing is the hint that it's time to ditch the booster (engines stops). You need to open the part info window to see when the tank is empty. 

If the challenge allow it (I know it's unlikely) Smart Part mod have the Drainex that trigger a staging even when you reach a previoly set % of fuel in the tank.

So now there no way to make it so that a stack can feed fuel to another one in only one direction? IOW,  even after I figure out how to set the priority numbers correctly, I'll still have to watch the fuel levels in those tanks to see when to jettison them? Bummer !

 

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Turn on advanced editor options, then turn off crossfeed on your radial decouplers. That should allow you to build old-style asparagus without monkeying about with fuel flow priority.

(The new method does work better, but hey, you do you)

Edited by Jarin

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Are you attaching the fuel hoses correctly (from first expended tank to the second expended.. Etc?) I can't make out the arrows of the feed lines from your screenshot.  The arrows on the green line seem to indicate you might be feeding from the inside out.

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1 hour ago, herbal space program said:

So now there no way to make it so that a stack can feed fuel to another one in only one direction?

AFAIK 'old' asparagus (fuel lines, crossfeed disabled) should still work the same. Maybe check your settings [fuel transfer obey crossfeed rules] ?

What I mentioned is the 'new' asparagus. Engines are able to use all tanks that are linked (attached directly or by decoupler/docking port with cross-freed enabled) and flow priorities define which  tanks are emptied first. 

The booster keep being used until the very moment you drop then, just getting fuel from the next tank available. The fact you can run the booster for more time is advantageous, while the lack of a more obvious clue that tanks get emptied is indeed a bit annoying.

Edited by Spricigo

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Just now, Spricigo said:

AFAIK 'old' asparagus (fuel lines, crossfeed disabled) should still work the same. Maybe check your settings [fuel transfer obey crossfeed rules] ?

Thanks, I'll check that the next time I get a chance to play. I also noticed that my outer stacks weren't actually separating the way they are supposed to, so maybe there was some  part clipping between adjacent tanks that was allowing fuel to flow in both directions. Unless struts can now transfer fuel.... can they? 

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Thanks for the screenshot, @herbal space program, but it's such a complex ship that it's hard to see anything at all-- just a jumbled mess (not your fault, it's just that it's hard to glean detailed 3D info from a single screenshot sometimes).

fCVTc8I.png

I'm not at a KSP computer at the moment, so I can't test this myself right now.  I'd love to see a really simple example you have that doesn't work, like this:

  • Center stack that has 1 fuel tank with 1 engine under it
  • Two (no more!) radial boosters, attached by radial decouplers that have crossfeed turned off
  • Radial booster is 1 fuel tank with 1 engine under it, and a fuel duct running from the radial tank inwards to the central tank

That seems to me like it ought to work exactly as you want and expect:  the radial boosters should drain completely before the central stack is touched at all, and the radial-booster engines should go dead as soon as their respective fuel tanks go dry.  If that's not what's happening for you, then something odd is going on here.

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2 minutes ago, Snark said:

That seems to me like it ought to work exactly as you want and expect:  the radial boosters should drain completely before the central stack is touched at all, and the radial-booster engines should go dead as soon as their respective fuel tanks go dry.  If that's not what's happening for you, then something odd is going on here.

Thanks for the input. I will try that the next time I get a chance to play.  As I noted above, one other thing that is going wrong is that those side stacks aren't decoupling properly, so maybe they are clipped into each other somehow. I doesn't really look that way in the VAB, but I dunno. I can try assembling the whole stack again and see. There are also a bunch of struts going this way and that. The other thing is that everything is put together with 4-fold symmetry, with the center stack attached using 4-fold symmetry to a single quad coupler above. I think maybe that type of configuration may cause some issues too. I guess putting together a Tylo lander using only items found in Jeb's Junkyard is not going to be a easy as I had hoped!

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One thing I noticed a few months ago is that it's quite easy to mess up putting six boosters around a same-size core on radial decouplers-- instead, getting (some of) the boosters stuck directly on the core tank.  If that occurs, not only won't the fuel flow work the way you expect (it'll act like one big tank feeding all the engines under it), the boosters won't stage off when you fire the decouplers.

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3 hours ago, herbal space program said:

As I noted above, one other thing that is going wrong is that those side stacks aren't decoupling properly, so maybe they are clipped into each other somehow.

Ah.  Now there is what looks to me like a smoking gun.  If decoupling isn't working as expected, it means you've got your decouplers set up wrong.  And since those decouplers are what you're counting on to interrupt fuel flow, it's not surprising if you've got problems there.  My guess would be that you've got a tank stuck to another tank, rather than being on the decoupler.

BTW, I just now had a chance to test asparagus staging, and it works just fine.

Here's a very simple ship that has just two boosters, asparagused to the central stack:

cFIPWn8.png

...This ship has crossfeed turned off for the decouplers (i.e. the default), and then as you can see, it has fuel ducts connecting the outer tanks to the inner one.  (The ducts go from the outer tanks to the center tank-- direction's not visible in the screenshot, just trust me that I got the direction correct.)  :wink:

Result?

vG6NzC2.png

All three engines fire.  The outer tanks drain first, as the inner tank is untouched.  When the outer tanks run out of fuel, the outer engines go dead and the center engine starts draining the center tank.  So, everything exactly as expected.

(Note that with the new crossfeed options available since 1.2, it's also possible to build this ship without fuel ducts-- just turn on crossfeed on the decouplers.  The one drawback in that case is that when the outer tanks run dry, the outer engines will keep firing, using the inner tank.  So in that case, you have to actually watch the fuel content of the tank in order to know when to jettison the boosters; you can't just watch for the radial engines to die.)

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6 hours ago, herbal space program said:

Unless struts can now transfer fuel.... can they? 

Fuel can in fact flow through struts and girders. If you mean strut connectors however, no it cannot.

Edited by Cpt Kerbalkrunch

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2 hours ago, Snark said:

 

...This ship has crossfeed turned off for the decouplers (i.e. the default), and then as you can see, it has fuel ducts connecting the outer tanks to the inner one.  (The ducts go from the outer tanks to the center tank-- direction's not visible in the screenshot, just trust me that I got the direction correct.)  :wink:

Result?

vG6NzC2.png

All three engines fire.  The outer tanks drain first, as the inner tank is untouched.  When the outer tanks run out of fuel, the outer engines go dead and the center engine starts draining the center tank.  So, everything exactly as expected.

(Note that with the new crossfeed options available since 1.2, it's also possible to build this ship without fuel ducts-- just turn on crossfeed on the decouplers.  The one drawback in that case is that when the outer tanks run dry, the outer engines will keep firing, using the inner tank.  So in that case, you have to actually watch the fuel content of the tank in order to know when to jettison the boosters; you can't just watch for the radial engines to die.)

Thank you for putting so much effort into this. I think my problem must be that either my tanks were touching or they are somehow not properly mounted on their decouplers. I guess in the past, having tanks touching or marginally clipped into each other did not result in actual resource flow, so maybe this is a new thing to me. In my own defense, I did check for this sort of thing in the VAB and it didn't look like any of that was actually happening -- but maybe I just need to look harder :blush:?. I'll get back to those who kindly replied when I figure out the truth of it....

28 minutes ago, Cpt Kerbalkrunch said:

Fuel can in fact flow through struts and girders. If you mean strut connectors however, no it cannot.

That is what indeed I meant, so I can eliminate that possibility. Thanks!

Edited by herbal space program

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2 hours ago, herbal space program said:

I think my problem must be that either my tanks were touching or they are somehow not properly mounted on their decouplers. I guess in the past, having tanks touching or marginally clipped into each other did not result in actual resource flow, so maybe this is a new thing to me.

Clipping or "touching" is (and always has been) irrelevant. The game neither knows nor cares whether one tank has any physical ( i.e. visual) contact with another.

What matters is *attachment*, which is another thing entirely. When you place a part on a rocket, it can only be attached to one part, a.k.a. the "parent" part. (I'm speaking of regular parts here, not struts or fuel ducts.)

It may be that you tried to attach a tank to a radial decoupler, but accidentally attached it to the decoupler's parent instead (i.e. another tank) in such a way that it looks as if it were on the decoupler. I don't actually know that that's your problem here... but suffice to say that if it were, you would not be the first person to encounter that particular issue. :wink:

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4 hours ago, Snark said:

It may be that you tried to attach a tank to a radial decoupler, but accidentally attached it to the decoupler's parent instead (i.e. another tank) in such a way that it looks as if it were on the decoupler. I don't actually know that that's your problem here... but suffice to say that if it were, you would not be the first person to encounter that particular issue. :wink:

I'll testify how easy it is to do this by accident.  I ran three launches in my science game before I figured out why my own asparagus was acting like a big dumb booster.

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7 hours ago, Zeiss Ikon said:

I'll testify how easy it is to do this by accident.  I ran three launches in my science game before I figured out why my own asparagus was acting like a big dumb booster.

Well, all I can say is those tanks sure looked like they were attached to the decouplers properly, and I did try taking them off and re-attaching them several times, but maybe they're still not on there correctly. I guess if they were, the tanks would decouple correctly, so there's that, Anyway, Like I said before I'll try rebuilding the whole assembly and see if it still doesn't work right for me. I have a feeling maybe the 4-fold symmetry of my core stack interfacing with the quad coupler above is causing some kind of "attachment issues" in the building interface. I  think I'll change that configuration as well and see if that produces better behavior.

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Checking if the attachment is correct is pretty simple. try to remove the decoupler and see what else come out together that is what is what you have further out in the tree structure of the craft.

Sometimes re-rooting may mess a bit with the routing. In any case it would be detectable with the testing above.

 

 

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4 hours ago, herbal space program said:

Well, all I can say is those tanks sure looked like they were attached to the decouplers properly, and I did try taking them off and re-attaching them several times, but maybe they're still not on there correctly.

One simple way to get bunches of tanks in place with the correct decoupler attachment is to attach one -- heck, build the whole booster in "one only" symmetry mode -- then duplicate the decoupler (which will duplicate everything depending on it) and put it aside in the bay, once for each additional pair of boosters you'll have (i.e. stash two dupes for a six-booster setup).  Then pick the single one off the core, change to 2x symmetry, stick it back on, attach your fuel pipes to the core, and (watching the staging order for the radial decouplers) put each of the duplicates on in 2x symmetry as well, and attach their fuel pipes.  This will ensure it's actually the decoupler you're sticking to the core tank/booster.

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8 hours ago, Spricigo said:

 

Checking if the attachment is correct is pretty simple. try to remove the decoupler and see what else come out together that is what is what you have further out in the tree structure of the craft.

Sometimes re-rooting may mess a bit with the routing. In any case it would be detectable with the testing above.

 

 

That was the ticket. Even though it totally  looked like everything was attached properly, the decoupler did not take anything with it when I pulled it off. Checking carefully, I can confirm that the tanks were not visually connected in any way, i.e. the VAB editor showed light through all their points of close apposition, yet still they are somehow connected. I'm pretty certain I never used the offset tool on those tanks either, so I guess it's just bad behavior by the building UI.  I know for certain there was a time when this sort of side-to-side attachment of tanks did not result in automatic transfer of resources, because I've had this issue many times before in earlier versions, and while the tanks didn't separate as expected, the engines attached to them still stopped when the tanks above them were drained, and they were drained in the correct order.  Since around 1.1 though, I've played almost exclusively with single-stage craft, so I guess that's why this is new to me.

Edited by herbal space program

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On 9/26/2017 at 6:47 PM, herbal space program said:

That was the ticket. Even though it totally  looked like everything was attached properly, the decoupler did not take anything with it when I pulled it off. Checking carefully, I can confirm that the tanks were not visually connected in any way, i.e. the VAB editor showed light through all their points of close apposition, yet still they are somehow connected. I'm pretty certain I never used the offset tool on those tanks either, so I guess it's just bad behavior by the building UI.  I know for certain there was a time when this sort of side-to-side attachment of tanks did not result in automatic transfer of resources, because I've had this issue many times before in earlier versions, and while the tanks didn't separate as expected, the engines attached to them still stopped when the tanks above them were drained, and they were drained in the correct order.  Since around 1.1 though, I've played almost exclusively with single-stage craft, so I guess that's why this is new to me.

That actually sounds to me like symmetry shenanigans borked your craft file. It happens sometimes when you try to symmetrically clone parts that themselves have symmetry on them (which sounds like what you've done with the quad-coupler). I've had that happen a few times before. See if there's other parts you can remove without taking the things that are supposedly "attached" to them. Sadly, if that's what's going on, your only option is "rebuilding from scratch in a new craft".

Edited by Jarin

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8 hours ago, Jarin said:

"That actually sounds to me like symmetry shenanigans borked your craft file. ... Sadly, if that's what's going on, your only option is "rebuilding from scratch in a new craft".

Yes, I think the root cause was that I tried to do unnatural things with symmetry and the editor wigged out.  I think maybe if you try to close a symmetry expansion back up, i.e. if you try to go from a single stack to a quad coupler attached to a 4-fold symmetrical stack of tanks, and then back to an upside-down quad coupler,  it makes some routine in there start to chase its own tail. I did that in my upper assembly, and thinking back I believe I did start to see some odd things after that. Quad couplers are a good way to interface 2.5m command parts with 1.25m stacks, which is what you have to do for this challenge, but I think you have to place each stack attached to them separately to avoid trouble. What happens in that case when  you open and close a symmetry bubble is that the upper and lower connectors end up being attached to only one of the 4 tanks in between, but you can easily paper over that with struts. I think that's how I'll proceed if I stick to that approach. 

Edited by herbal space program

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17 hours ago, herbal space program said:

if you try to go from a single stack to a quad coupler attached to a 4-fold symmetrical stack of tanks, and then back to an upside-down quad coupler,  it makes some routine in there start to chase its own tail

Actually that's just not possible at all. If you try it, only one of the four nodes on the bottom actually attaches. (I recall a mod that could make this work, but it may have been a fever dream). The reason is, the craft file is a tree. Like a tree, once branches split, they can't merge back together (well, like most trees anyway). There has to be a single path from every single part through its parents to a root part. Couldn't see any couplers in the image or I'd have brought that up earlier (as would a bunch of other people, I suspect).  So... probably looking at a number of issues then.

Edited by Jarin

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10 hours ago, Jarin said:

Actually that's just not possible at all. If you try it, only one of the four nodes on the bottom actually attaches. So... probably looking at a number of issues then.

Yes, I get that ships are all trees, although I did build this once! https://imgur.com/a/3UtXF

I'm sure that station is actually a tree too, but docking port magnetism can make structures behave mechanically as if they are in a circle. Anyway, I think in this case, it wasn't necessarily the logic of the ship that got corrupted, but just that the visual rendering engine failed to represent  the way things were connected faithfully.  I've long since scrapped that ship, and the rebuilt version seems to be behaving as expected. I still don't quite understand how the new tank priority system works, but I'll figure it out. I appreciate all the help though!

 

Edited by herbal space program

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47 minutes ago, herbal space program said:

I still don't quite understand how the new tank priority system works, but I'll figure it out.

  1. Tanks with higher numbers drain before tanks with lower numbers.
  2. By default, all the tanks on a stage have the same priority, unless you tinker with it manually.
  3. They've done a clever thing:
    • The actual number that a tank gets is the sum of two things:  a "stage" component, and a "manual" component.
    • The "stage" component is a multiple of 10, and is purely controlled by "what numbered stage is it on".  The higher the stage number, the higher the number.  10, 20, 30, 40, etc.
    • The "manual" component is the delta you apply by clicking the + and - buttons.  Each click is 1.
    • So, if a tank had a priority of 30 (because of the stage it was on), and you click the + button, now it has 31.

That "manual + stage" idea is remarkably clever, IMO.  It means that in most cases, things just naturally do what you want:  for example, if you attach a tank radially with a radial decoupler, and enable crossfeed on the decoupler, then the radial tank will drain first and then you can jettison it-- which is almost certainly what you want.  It also means that you can tinker with settings, and they get preserved if you change the staging on your ship.  Let's say you have a stack of two tanks and you want the bottom one to drain first, so you give it a +1.  Then you change your mind and you move the whole stack to a different stage of the ship:  they all change wholesale by 10, 20, 30 etc. so they have the right overall sequence number relative to the other stages on the ship, but it still preserves "bottom one drains first" because it still has that +1 on it that you gave it.  And if a rare oddball case comes up where you actually want a higher-numbered stage to drain *after* a lower-numbered stage, you can just click the +/- button a lot to give it any priority you want.

I really like how they've set it up.  It means that most of the time, I don't have to mess with it at all and it just naturally does what I'd want it to do anyway.  The few times I do use it are when I've got two or more fuel tanks stacked vertically, and I want the bottom one to drain first (for stability's sake); so then I just put a +1 on the bottom tank and I'm done.

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