No Thrust From Engine - Was Working, Now Broken

[archiebald 39]

Mid Career game on 1.8.1 in Windows 10.  I have a NERV powered freighter ship that shuttles ore and fuel between stations in Kerbin & Mun orbit - I've been using it for a while with no problems, it has made at least return 10 trips.  Now suddenly, after having been docked to the Kerbin station for a while, I've had thrust problems.

When I undocked and backed away I noticed that the RCS seemed almost powerless - this ship is empty but it acted as if it was really massive.  Then I made a node to go to the Mun and fired up the main engine.  Engine lights, fuel is consumed but the thrust is zero - there is no acceleration and the delta/v meter (just right of the navball) does not decrement as normal.

I used another vessel  to pull it away from all other's physics ranges then left it in free space just as a test but still no thrust.

I have numerous mods installed, but none have changed for the last several weeks.  I'm don't use steam and I use CKAN so I control when game files and mods update - none has been done since the ship was last working.  All my other 30 or so ships I have in space now are unaffected, even three others that are NERV powered.  On this problem ship the NERV is just sticking out the back, so no obstructions and no design changes.

There's a few very old topics on this but all are related to new ship builds, or incorrect builds.  This was working perfectly but now it isn't.

Any clues where to start debugging would be welcome.  If all else fails I will terminate the vessel and cheat a replacement into orbit, but I don't like unsolved puzzles.

[AHHans 974]

Did you check the mass of the vessel? If you have an asteroid in tow, then you may be affected by bug #24855.
[Edit:] Oh, you said you are using 1.8.1, so the asteroid bug shouldn't affect you, but still a good idea to check the vessel mass.[/Edit]

Edited May 21, 2020 by AHHans

[archiebald 39]

No asteroids are involved.  It is a fuel and ore freighter.

Unless the mass is infinite, I don't think it is a mass problem because I can run the engine till the tanks empty and the orbital velocity doesn't change by even 0.1 m/s and apo/peri don't change at all.

[AHHans 974]

Hmmm... that would happen if the thrust was occluded, i.e. if there is a part of the vehicle in the way of the exhaust. But you wrote that there is nothing in the way of the exhaust. And the only other way that thrust occlusion makes itself known is by heating the occluding part.

So, sorry, I don't have a good idea what your problem is.

[archiebald 39]

No the NERV sticks out into space and as I said, it has been flying around the Kerbin system for the las 1 year of game time (last few weeks IRL).  Pretty sure something has become corrupted, just strange and unusual.

[Zhetaan 900]

1 hour ago, archiebald said:

No the NERV sticks out into space and as I said, it has been flying around the Kerbin system for the las 1 year of game time (last few weeks IRL).  Pretty sure something has become corrupted, just strange and unusual.

If it's not a bug, then the only other possibility that comes to mind is that one of your mods treats the Nerv's nuclear component as subject to radioactive decay, thus giving the engine a finite service lifetime.

Otherwise, you may need to get into your persistent file to obtain more information.

[archiebald 39]

Thanks for trying, I've never heard of decay in a NERV before.  Here's the thing - I went to my VAB, and loaded a new copy of the saved ship design and cheated it to orbit using Hyperedit. - It had the exact same problem.  In addition, this time I noted that the RCS also produced no movement or thrust either.  I proved this by adding a separator with zero separation power.  After activating it, both the main engine and the RCS would not move the ship away from the separated parts - after about 5 minutes they just very slowly drifted apart.

I then went back to the VAB and built a new clone of the ship using identical like-for-like parts in all the same positions throughout right down to the solar panels and antennae, launched that version via Hyperedit and it works perfectly.

So somehow both my original saved ship in the persistent file as well as the original craft file that I loaded in a second time seem to have had some form of corruption.  Remember this was a design that had been operating perfectly before.  Very weird.

I've solved the problem now by terminating the bad ship and replacing it with the rebuilt version.

[AHHans 974]

9 hours ago, archiebald said:

Here's the thing - I went to my VAB, and loaded a new copy of the saved ship design and cheated it to orbit using Hyperedit. - It had the exact same problem.

Do you still have the *.craft file of this broken ship? Could you put it somewhere where I can download it?

[archiebald 39]

Sure, I'll upload it to a DropBox account when I get home tonight.

You might need the mod Configurable Containers as I have the fuel tanks adjusted for carrying Ore and Xenon as well as LF.  I also run Restock, but I think that is only cosmetic.

I'll also upload the re-built version which works.

[archiebald 39]

Okay, so I have uploaded it here as well as a rebuilt copy that works.  Names are KSF Aztec (no thrust) and KSF Aztec II

The TD-25 decoupler is only there to keep it upright on the launchpad while I am getting Hyperedit set up.

https://www.dropbox.com/sh/xopka6gcfxn3rsc/AABSxUybfjFg77goVskh4bHqa?dl=0

[Zhetaan 900]

16 hours ago, archiebald said:

Thanks for trying, I've never heard of decay in a NERV before.

I know that Near Future Electrical treats the Nerv reactor as a finite-lifetime nuclear reactor (that's not exactly the same as radioactive decay, but there are mods that process decay, too).

I'm not running your mod loadout and so won't be able to do a proper comparison, but yes, it appears that something was saved incorrectly or otherwise didn't work right.  Unfortunately, with the way that the saves work, these errors tend to perpetuate rather than self-correct.  Your solution may have been the only viable one.

[archiebald 39]

9 hours ago, Zhetaan said:

I know that Near Future Electrical treats the Nerv reactor as a finite-lifetime nuclear reactor (that's not exactly the same as radioactive decay, but there are mods that process decay, too).

Ah, okay - I am not running anything like that and as I said, the RCS is also producing zero thrust in that craft.

I can understand the craft in flight having a problem because the persistent file got borked by a crash for example, but I don't understand why the craft file of that ship is having the same problem - we are talking about two separate files here.

As far as I know, when you reload a savegame, it does not reference the craft files.  It can't because I have some craft in flight for which I already deleted or modified the craft files for.  So in this case something is causing the same error in the persistent file AND the craft file.  If the problem was there from first flight I could understand but as I said, this vessel carried out multiple trips within the Kerbin system before going cuckoo.

Edited May 22, 2020 by archiebald

[AHHans 974]

8 hours ago, archiebald said:

I can understand the craft in flight having a problem because the persistent file got borked by a crash for example, but I don't understand why the craft file of that ship is having the same problem - we are talking about two separate files here.

Indeed! My guess is that some part of the "game" - probably a mod - got updated and that this caused the craft to get screwed up.

[Zhetaan 900]

On 5/22/2020 at 6:55 PM, archiebald said:

I can understand the craft in flight having a problem because the persistent file got borked by a crash for example, but I don't understand why the craft file of that ship is having the same problem - we are talking about two separate files here.

As far as I know, when you reload a savegame, it does not reference the craft files.  It can't because I have some craft in flight for which I already deleted or modified the craft files for.  So in this case something is causing the same error in the persistent file AND the craft file.  If the problem was there from first flight I could understand but as I said, this vessel carried out multiple trips within the Kerbin system before going cuckoo.

That is correct, but it's also important to remember that the persistent file and the craft files use the same format and language, so a problem that can corrupt a craft in the persistence can corrupt a craft in the ... craft.  That would lead me to suspect something more like @AHHans suggested and that there was an update that changed or broke something in that specific craft, and considering how long you've been using it, it's possible that perhaps there was an update in there even though you said you've not updated recently.  If it was an update, then I suppose it could be called a glitch rather than a bug, but either way, the only effective remedy I know is to do exactly what you did.

[JoeSchmuckatelli 371]

On 5/21/2020 at 6:45 AM, archiebald said:

No asteroids are involved.  It is a fuel and ore freighter.

Unless the mass is infinite, I don't think it is a mass problem because I can run the engine till the tanks empty and the orbital velocity doesn't change by even 0.1 m/s and apo/peri don't change at all.

Is the ship driven by a probe core... And do you have an antenna extended?