sepratrons not firing with stage

[zeppelinmage]

Here's my problem.

I have a large asparagus lifter rated for 75 tonne payloads. It lifts fine, until I stage the first pair of boosters. (See images below.) Because of the rather wide motor mounts on the center stack (it's an array of 9 LV-T45s using tail connectors as mounts), I had to "stand-off" the stages. Now,when I stage, the radial mounts impact the tail connectors, causing catastrophic spontaneous energetic disassembly.

I've figured a solution to the problem: sepratrons. I've mounted a pair on each stack, expecting them to fire when I stage and add some distance between the lifter and the spent stages. Except... the sepratrons don't fire when I stage. (Yes, I double-checked the staging to be sure they were on the right one.)

Thoughts?

In the VAB, here's the business end of the lifter:

And the staging issue:

Notice the inert sepratrons on the grey tanks.

Edited March 8, 2014 by zeppelinmage

[SRV Ron]

If staging is clean, where the spent boosters are dropping off without hitting anything, just eliminate them. Those should be firing if they are on the correct staging location.

[zeppelinmage]

Staging is clean until the radial decouplers impact the tail connectors.

And the sepratrons aren't firing despite being on the correct stage. (Note my staging in the VAB image.)

That's the problem I'm trying to solve.

[Kryxal]

Maybe try putting the sepratrons on their own stage just below what they're splitting off, and do two stages to drop? It's not exactly ideal, but it might work...

[Claw]

I have had similar problems with other staging events and separating a payload from a carrier..

Sometimes rearrainging the order of separatrons/decouplers inside the staging block helps. i.e. Put the separatons above the decouplers, but still in stage 9. If that makes sense.

I'm not sure if the game executes the staging block from the top down or what. Sometimes I see this, and sometimes I don't.

Edit: That's a nice looking rocket.

Edited March 8, 2014 by Claw

[Pecan]

I concur with Claw - your staging looks fine provided those are the correct separatons in stages 7 - 9 (I'm sure that's what you've already checked and anyway you'd see the 'wrong' ones firing on still-attached tanks if they weren't) so unless you've disabled them in the VAB it's probably an artefact of the game.

Another consideration with separatons though - they are currently pointing at your central tank and when they fire you'll likely get damage recorded in the flight-log (F3). I've never seen any actual damage from them but you might find they work better - once you get them working at all! - so they push 'up and out' rather than just out. I think Kasuha wrote an article on separaton placement but I can't find a link to it at the moment...

[Edit: Thank you Red Iron Crown :-)]

Edited March 8, 2014 by Pecan

[Red Iron Crown]

I think Kasuha wrote an article on separaton placement but I can't find a link to it at the moment...

http://forum.kerbalspaceprogram.com/threads/71326-How-to-mount-sepatrons

[Vanamonde]

zeppelinmage, I know you're not a newbie, but it's easy to overlook the obvious stuff sometimes. It's very easy to confuse oneself about which side stack is which, and that sort of thing. Mouse over the sepratrons themselves and make sure the ones you want to fire have their boxes on the staging display show the white border, or mouse over the staging icon and see if the right sepratrons turn green. It's likely you simply have the sepratrons from one asparagus stage assigned to the boosters of another. (I do this all the stupid time. )

Edited March 8, 2014 by Vanamonde

[zeppelinmage]

Thanks for the tips, guys.

I'll check the order within each stage and see if that helps. I'll also check Kasuha's tutorial.

[Claw]

Ahh, the other thing I forgot to mention (I've mostly noticed this on launch clamps). Sometimes holding down the space bar when you stage helps, instead of just tapping it. Occasionally I get a sticky launch clamp that doesn't want to let go if I don't hold the space bar. Not sure what the cause of that is.

[Kasuha]

Order of icons in the staging column does not make a difference, sepatrons always fire for me when they're separated.

Except for what Vanamonde mentioned, maybe also right-click your sepatrons in VAB if you didn't accidentally tweak them to zero fuel and/or zero thrust.

[zeppelinmage]

Order of icons in the staging column does not make a difference, sepatrons always fire for me when they're separated.

Except for what Vanamonde mentioned, maybe also right-click your sepatrons in VAB if you didn't accidentally tweak them to zero fuel and/or zero thrust.

I just triple-checked this to be absolutely sure. They are on the correct stages, and fueled.

Sometimes rearrainging the order of separatrons/decouplers inside the staging block helps. i.e. Put the separatons above the decouplers, but still in stage 9. If that makes sense.

This fixed the issue. Sepratrons fire as designed now, and my asparagus stages properly. (Of course, the fix may also have been due to restarting the game.)

[Kasuha]

This fixed the issue. Sepratrons fire as designed now, and my asparagus stages properly. (Of course, the fix may also have been due to restarting the game.)

I tested the icon order and both orders (sepatrons above decoupler or sepatron below decoupler) did exactly the same for me, i.e. sepatrons ignited and decoupled.

So my guess is it was the restart.

[zeppelinmage]

I tested the icon order and both orders (sepatrons above decoupler or sepatron below decoupler) did exactly the same for me, i.e. sepatrons ignited and decoupled.

So my guess is it was the restart.

That's my feeling as well.

For the record, I tried your suggested placement, but the stack didn't rotate enough to clear. I'll accept some minor stack scorching to keep it intact.

[Yarrula]

I have had similar experiences. I always put the sepatrons above the decouplers. They never fire consistently if the decouplers is first in the stage. If I put them first, they fire 100%. Strange behaviour indeed.

[Claw]

I tested the icon order and both orders (sepatrons above decoupler or sepatron below decoupler) did exactly the same for me, i.e. sepatrons ignited and decoupled.

So my guess is it was the restart.

I'm not saying I don't believe this, but I will say that I have encountered this problem before. I will also say that I've had many rockets that order didn't affect. And I'v had it with more than just sepratrons (like chutes or engines). When I did have this problem, I was able to fix it by changing the order inside the stage.

Perhaps it isn't that the order matters, but there is some other bug. And maybe changing the order OR restarting fixes it?

[Gargan]

I'm not saying I don't believe this, but I will say that I have encountered this problem before. I will also say that I've had many rockets that order didn't affect. And I'v had it with more than just sepratrons (like chutes or engines). When I did have this problem, I was able to fix it by changing the order inside the stage.

Perhaps it isn't that the order matters, but there is some other bug. And maybe changing the order OR restarting fixes it?

I was having the same problem as OP where one of my outer stage's sepratrons were not firing during that stage's decoupling. I even replaced the sepratrons with Ullage motors from KWR thinking that might help, but no go. I was always under the assumption that the order within the stage had no effect and thus no reason for me to worry or bother. After verifying that they were correctly staged and a multitude of testing I started searching around for sepratrons not firing and found this post. And I can decidedly say that rearranging the order such that the sepratrons were above the decouplers is what fixed it. I never restarted KSP throughout this process and the only thing that worked was the rearrangement. This has to be some type of bug in how each part within a stage is set off. It also might have something to do with how many parts total are being simulated as my setup is rather large and starting to slow my simulation time down a bit. I wonder if that is why one of my inner stages with sepratrons has always worked as expected, irrespective of order within the stage. Maybe once the simulation starts to slow down with all the physics calcs some sort of timing issue pops up. I don't know, but I just want to say thanks for at least helping me out with this issue I was having.

[Kasuha]

I was having the same problem as OP where one of my outer stage's sepratrons were not firing during that stage's decoupling. I even replaced the sepratrons with Ullage motors from KWR thinking that might help, but no go. I was always under the assumption that the order within the stage had no effect and thus no reason for me to worry or bother. After verifying that they were correctly staged and a multitude of testing I started searching around for sepratrons not firing and found this post. And I can decidedly say that rearranging the order such that the sepratrons were above the decouplers is what fixed it. I never restarted KSP throughout this process and the only thing that worked was the rearrangement. This has to be some type of bug in how each part within a stage is set off. It also might have something to do with how many parts total are being simulated as my setup is rather large and starting to slow my simulation time down a bit. I wonder if that is why one of my inner stages with sepratrons has always worked as expected, irrespective of order within the stage. Maybe once the simulation starts to slow down with all the physics calcs some sort of timing issue pops up. I don't know, but I just want to say thanks for at least helping me out with this issue I was having.

I returned to it and did a few experiments.

First of all, it looks like order in which you set them up in VAB is irrelevant - when putting it on launchpad, order of parts within stage resets to default. Then I tried playing with stages on launchpad and once I managed to fire a decoupler and its sepatrons did not fire. Unfortunately I'm not sure what exactly did I do with the staging before that. In all other attempts sepatrons fired.

Internally the game appears to hold staging order (even order in which parts are activated with stage) separate from the order in which parts appear in staging column. So I really don't know but there may be some sort of bug involved.

[MarvinKitFox]

I've had some very bad experiences with firing seperatrons during staging. Up to even a design made with full 2-way symmetry firing one side's seperatrons and not the other.

As I only need to use seperatrons on ships of "gargantuan" class or larger, I don't know for sure if vessel size/complexity plays a role.

My solution is to not use seperatrons for stage-separation collision avoidance. I rather just use double-layer Tt-70 radial decouplers.

They provide twice the clearance, and twice the "shove" ensuring clean seperation, as long as it is mounted anywhere near the centre of mass of the empty decoupled bit.

Yes, the inner decoupler's debris then inevitably impacts my core rocket, but it never breaks anything, just adds some fireworks.

If I *must* use seperatrons, I put them on a separate stage to activate just before decoupling. They last plenty long enough for that.

[Aethon]

Interesting.

I'm having this problem right now- seperatrons won't fire with the rest of their stage. I decided to restart to see if that does the trick ( and browse the Forums ) when I stumbled on this post. I have not rearranged the stages yet so I can do a control experiment to see if a restart fixes this.

Brb.

K, I launched the same rocket directly after restart and the seperatrons again failed to ignite. I then dropped the seperatrons above the decouplers in the staging and it worked fine. I had always assumed that order within a stage was irrelevant.

Perhaps this should be moderated to Bugs?? Is it a bug? I mod only Chatterer, Kerbal Alarm clock and Kerbal Engineer Redux.

Edited May 26, 2014 by Aethon

[James_Eh]

I don't know as much about the nuts and bolts of this game as many of y'all, but... Could this be a case of processor cycles with big, lagy ships? If the seperatrons are at the bottom of the list of things to detach, and the game works through them one by one, and the first thing it does is blow the stack decouplers, could it then decide (in the next calculation iteration) that the seperatrons are no longer linked to any control-enabled thingies and thus just ignore the "fire" command?