Farsyte

When I get a chance, I'll rerun trying to match your configuration, and see if I can isolate which change in particular causes the crossfeed to stop. Might be a while (too many irons in the fire!). It will probably be something really stupidly simple. I have this sixth sense of when a "headdesk" moment is coming ... The fuel tank priority coupled with cross-feed is definitely preferable to running ducts around. [EDIT after reproducing Sir Frost's configuration] Yeah, it *was* something stupidly simple. All this is still KSP-1, of course. 1. Yes, The tanks that are connected by cross-feed do indeed drain strictly in priority order. This is visible if you actually show the fuel levels in each tank. 2. When the first pair of tanks is empty, the cross-feed and fuel-duct configurations have a critical difference: the engines attached to the drained tanks still have access to the fuel in the others. This leads to 3. The staging display shows fuel available to the engine, not fuel in the tank stack it is attached to. Even after a decade, this one is still learning how to read the User Interface. 4. Since the engines in the drained stages still have access to fuel, the engines are not marked as "flamed out" and they still provide their full thrust to the available thrust totals. My personal conclusions: A. I like the idea of using cross-feed and tank priorities (but note, this does not exactly match the fuel duct use case). B. I am going to need a more complicated auto-stager since I can't use "flameout" or "availablethrust" to detect that staging is a good idea right now. I'll have to identify which tanks are jettisoned by each staging event, and trigger staging when those tanks are empty (probably by watching the vessel mass total). C. Until I work out the new autostager, I'm personally stuck with fuel ducts, as I do a lot of mission automation. [k-OS fan]

This is all KSP-1 stuff. I'm hoping that the situation laid out below did not flow into KSP-2. Since I don't see fuel tank priorities in KSP-2, it seems like KSP-2 Asparagus configurations will need fuel ducts. If I see fuel tank priorities in KSP-2 I will certainly try to use them instead! TLDR: cross-feed and tank priorities would obsolete fuel ducting, except that cross-feed in TT-38k and TT-70 is broken in KSP-1. I did not check other radial decouplers, since Asparagus staging is most critical to me in early career when few parts are available (it makes hitting Mun and Minmus massively easier). More explicitly before more "you need to unlock it" and "you need to enable it" and "did you check the fuel feed overlay" ... ( As a software engineer, I spent a lot of time writing "did you turn it off and on again" style replies. we can skip that part of diagnosis, thanks. ) With cross-feed unlocked in R&D, and the option visible, and the option turned on in each mounted decoupler, and fuel priorities set for the tanks, and the fuel overlay showing fuel should flow where I want it to, I launch and observe all tanks in the asparagus staging set-up are being drawn down at the same rate. Historically I have depended on a seven-engine configuration using TT-38k, FL-T800 and FL-T400 tanks, and a mix of Reliant and Swivel engines. I just crosschecked with the TT-70 obtaining the same result. Options set, overlay in VAB shows it should flow, but tanks drain evenly in flight. So. At this moment, when it comes to Asparagus configurations in KSP-1, fuel ducts are needed and not actually obsolete. https://wiki.kerbalspaceprogram.com/wiki/TT-38K_Radial_Decoupler lists the following changes relating to fuel ducting, radial decouplers, and cross feed: > 0.9 - August 12, 2011 - (undocumented) Radial decouplers can now cross-feed fuel >0.13.1 - January 11, 2012 - Removed parent-wise fuel cross-feed from Radial Decouplers. Fuel Lines made that obsolete https://wiki.kerbalspaceprogram.com/wiki/TT-70_Radial_Decoupler Size aside, the TT-70 functions identically to the TT-38K Radial Decoupler > 0.18 - 1 December 2012 - Initial Release https://wiki.kerbalspaceprogram.com/wiki/FTX-2_External_Fuel_Duct has wording that agrees with what you say, and what I remembered, but see below: Fuel lines used to be a vital part of asparagus staging designs allowing for use of all engines available where fuel is first drained from external fuel tanks allowing them to be jettisoned (severing the FTX-2 External Fuel Duct) when they become empty. By the time the last external fuel tanks are jettisoned, the central or main fuel tanks left on the vessel will be at a full fuel level. Nowadays, most of this is done by setting the flow priorities appropriately, and fuel lines are no longer necessary for asparagus staging. relevant change log entry: >0.13 - December 16, 2011 - initial release So why do I still use fuel ducts? Because fuel cross-feed in the TT-38k radial decoupler is broken. Yes, I've upgraded R&D. I see the option in each decoupler placed, and I've turned it on (it defaults to off). I have double checked that the tanks have their priorities set. Despite all indications in the UI that it should work, all of my tanks are draining equally; no fuel is being cross-fed, in any direction, between any of the tanks in my asparagus launcher.

So very very glad you are working on this! Time to study your .TO2 language

You know, I never attempted to use the crossfeed system, in favor of always laying out explicit ducting. Will have to try it. quick update to save anyone time who is following in my footsteps: the radial decoupler I use in KSP-1 (TT-38k, the first one we get) briefly supported fuel crossfeed but that was removed, in January 2012, because fuel ducts made it obsolete ... Yeah, I found out when digging around after being unable to get it to work, because the TT-38k still has an option to enable and disable crossfeed. Moved over to KSP-2 and ... well, didn't find crossfeed and fuel tank priority options, but I may not have looked hard enough. I'll just wait for Patch Two before I start launching my veggies.

I tend to use Asparagus staging (using fuel lines to keep inner tanks topped up, staging away outer engine/tank sets) and it seems like this is only partially functional in KSP-2: it appears that some fuel flows but not enough to keep inner tanks topped up. Adding more fuel lines does not change the results. I did a walk through of the situation, showing what I expect (using KSP-1) and what is actually happening in KSP-2. I have sent this in via the launcher feedback. I did not post here before because I thought I saw it already covered - but checking today, I only see mentions of Asparagus not being reliable in KSP-2; the fuel flow issues I see may or may not be related. I am hopeful that the team working on the performance issues around fuel flow have already nailed this, but here's a video of the symptom so you can see exactly what is troubling me. I think I managed to convince myself this is not merely a display bug ...

Noticed that I could analyze my low resolution scan data and get science, and radio it back. But on an earlier mission, I did the Analyse while in Mun orbit, shut down the scanner and returned the package to Kerbin (was unable to grab the data during EVA, ended up bringing my whole orbiter back rather than just the return capsule ... fun flight!) ... and did not get the science for it (yeah, poked around in the persistant.sfs file, it shows cap=60 but sci=0). Still tinkering with this part, I assume?