mechjeb is confusing me....as always.

[putnamto]

ok, so i have noticed that my vessel has two different total dv numbers, one in the vab, and the other on the launch pad.




could this have something to do with the fact that i build everything inside of the fairing as one craft, then added the boosters, tank, and mainsail?

[Zhetaan]

Something is going on with your upper-stage engine--or engines, most likely.  Your lower stage has the same TWR and the whole rocket has the same mass so you didn't remove payload, but you went from a sea-level thrust-to-weight ratio of .08 to .14 between VAB and pad with no change in burn time.  Absent an altered payload mass, that suggests to me that you have multiple isolated engine-fuel stacks mounted on the upper stage, but that for some reason, one or more of them was shut off in the VAB or else MechJeb was blind to it for some reason.  If the engine-fuel stacks are identical, then the burn time would be the same, but the delta-V would be very different.

On the other hand, are you using multi-mode engines?  I don't know how well MechJeb handles engines that can burn fuel in different ways.

Did you launch the rocket?  Which value was accurate?

[Gargamel]

I have found that MJ is kinda hit or miss on it's DV estimations.    Have a sepatron pointed in a non-prograde direction anywhere on the ship?  Then you often can't trust the estimates.  Use throttle control to increase your second stage dv?  Yeah, MJ is blind to this while in the VAB. 

I don't have an answer for you, as there are dozens of little things that I have found that will throw off the estimates.  Once you've recognized the issue, and can see what the real values are, then you can mentally adjust the estimates.   If there's a fix for it, that's great, but till then, I usually go by the seat of my pants. 

[putnamto]

ive done a test orbit and it still had almost 5k dv left.

the upper stage inside of the fairing is just a fuel tank, sas, some solar panels, some dockotrons, rcs and those little orange radial mount engines.

going to be part of my moon space station, i guess ill try to fly it up their and if it doesnt make it ill just point it at the sun and forget about it lol.

EDIT:

heres another vessel that does the same thing, 

the funny thing is though, if i take the lower stage from the rocket in my first post, and attach it the the vessell in my second post i dont get these same results, the dv stays the same in the vab and the pad.

i did just notice that mechjeb makes a ghost 5th stage with 0 across the board in both cases, a bug or broken mechjeb maybe? i did recently do an os reinstall and litterally just moved my entire installation folder from my old build to this one, maybe that messed something up.
 

[Gargamel]

I have the same ghost stage.  I always assumed it was just the way MJ worked, it disappears as you launch.    Maybe @sarbian can shed a little light, or we can have a mod merge this into the MJ thread....

[sarbian]

Can't help. Your version is 9 months old.

[putnamto]

3 hours ago, sarbian said:

Can't help. Your version is 9 months old.

my mechjeb?

[sarbian]

Clearly not mine

[putnamto]

2 hours ago, sarbian said:

Clearly not mine

so your saying i should update my mechjeb?

EDIT i just installed the latest mechjeb, and im still getting different numbers in vab and on the pad, and still getting the ghost stage.

im also getting a dv read on stages that have no engines, no rcs, just a decoupler a science pod and some electrical stuff.

 

Edited February 24, 2018 by putnamto

[putnamto]

this game is either buggy as hell, or im seriously screwing something up.

while trying to figure out my mechjeb problem i noticed that i can no longer deploy solar panels in the vab or anywhere really.

going to reinstall, then if that doesnt work im just going to give up i dont have time to just sit here trying to figure out why that thing worked yestarday and doesnt today.

[HvP]

@putnamto have you tried seeing what the KerbalEngineerRedux mod shows? For all I know the two mods may just draw their deltaV numbers from the same code but seeing how a different mod shows the stage dV might give a clue as to where the discrepancy lies.

[putnamto]

I  did  the  reinstall  and  put  all  the  mods  in  with  can,  I'm  still  getting  weird  numbers  though. And  a  ghost  stage.

Ill  try  getting  engineer

I  think  I  figured  out  the  problem!

When  I  built  my  ships  I  would  build  the  top  stages(the  fairing) as  one  craft, then  save  it  and  build  the  bottom  stage  as  another  craft  and  merge  them.

I  think  mj  ignores  the  merged  part  till  we  get  to  the  pad.

[putnamto]

ok, some more trying to figure this out. mj and engineer give the same readouts.

but if i put my booster and my core engine in the same stage i get a different dv than if i put them in seperate stages. i think this is just user error now.

 

[HvP]

1 hour ago, putnamto said:

ok, some more trying to figure this out. mj and engineer give the same readouts.

but if i put my booster and my core engine in the same stage i get a different dv than if i put them in seperate stages. i think this is just user error now.

 

I'm wondering if it might be a complication of fuel flow priority being changed on those Rockomax tanks. I don't know how MechJeb or KER handles fuel flow priority, but it could have a huge impact on delta-v if that large decoupler had its crossfeed enabled.

Edited February 25, 2018 by HvP

[HvP]

@putnamto I think the ghost stages that are all zeroed out might represent your fairings which I'm guessing were in their own stage before you disabled the staging for them. Just as an experiment: what happens if you reassemble the ship without the fairing components?

[putnamto]

6 hours ago, HvP said:

@putnamto I think the ghost stages that are all zeroed out might represent your fairings which I'm guessing were in their own stage before you disabled the staging for them. Just as an experiment: what happens if you reassemble the ship without the fairing components?

i didnt do exactly that but after a new install and all the mods through ckan im still getting the ghost stage, even on a simple ship(no fairings at all)

[HvP]

21 hours ago, putnamto said:

i didnt do exactly that but after a new install and all the mods through ckan im still getting the ghost stage, even on a simple ship(no fairings at all)

Ok, I think I've figured it out after taking a look at my own install.

In the VAB MechJeb seems to calculate fuel usage inward toward the root part (or something like that.) Using the re-root gizmo (the one that looks like a Z next to the rotate tool) you can choose a new root part for your rocket stack, and when one of the parts in the middle of the stack is chosen as a root part it will drastically reduce the reported delta-v. It's as if MechJeb stops calculating the fuel contribution of tanks above the root part. When you launch the same ship it seems to correct this error and calculates the stages normally again.

The first part you place in the VAB automatically becomes the root part unless you change it with the re-root tool. I would recommend making sure that your final command pod is always selected as your root part if you want MechJeb to report correctly in the VAB. It's usually best practice to start building from your topmost command pod first and work downwards and this is probably the assumption that MechJeb uses. This also explains why your stages reported differently when you merged the ship in the VAB.

This may be intended behavior, I'm not sure but maybe @sarbian is already aware of this result.

The zeroed out stages represent those staging events where you press the space button but don't necessarily have a delta-v number associated with them. For example, staging a decoupler or activating an engine for the first time. The stage that shows the engine activation isn't shown in the VAB but it gets added to the bottom of MechJeb's delta-v list on the lauchpad. You can see that zeroed out stage disappear in MechJeb's delta-v list if you set throttle to zero and then hit the spacebar on the launchpad.

Also, MechJeb is automatically taking elevation into account even when on the launchpad. In the VAB the numbers are calculated for 0 meters elevation, but depending on the height of your rocket some engines could be 100 meters above sea level when resting on the launchpad. This will only minimally affect the delta-v stats but it does explain some small discrepancies.

I hope this is what was causing your problem. Do let me know if it helps.

Edited February 26, 2018 by HvP

[putnamto]

3 minutes ago, HvP said:

Ok, I think I've figured it out after taking a look at my own install.

In the VAB MechJeb seems to calculate fuel usage inward toward the root part (or something like that.) Using the re-root gizmo (the one that looks like a Z next to the rotate tool) you can choose a new root part for your rocket stack, and when one of the parts in the middle of the stack is chosen as a root part it will drastically reduce the reported delta-v. It's as if MechJeb stops calculating the fuel contribution of tanks above the root part. When you launch the same ship it seems to correct this error and calculates the stages normally again. I would recommend making sure that your final command pod is always selected as your root part if you want MechJeb to report correctly in the VAB. This also explains why your stages reported differently when you merged the ship in the VAB.

This may be intended behavior, I'm not sure but maybe @sarbian is already aware of this result.

The zeroed out stages represent those staging events where you press the space button but don't necessarily have a delta-v number associated with them. For example, staging a decoupler or activating an engine for the first time. The stage that shows the engine activation isn't shown in the VAB but it gets added to the bottom of MechJeb's delta-v list on the lauchpad. You can see that zeroed out stage disappear in MechJeb's delta-v list if you set throttle to zero and then hit the spacebar on the launchpad.

Also, MechJeb is automatically taking elevation into account even when on the launchpad. In the VAB the numbers are calculated for 0 meters elevation, but depending on the height of your rocket some engines could be 100 meters above sea level. This will only minimally affect the delta-v stats but it does explain some small discrepancies.

I hope this is what was causing your problem. Do let me know if it helps.

holy crap i think this is it, i dont bother changing the root part once i merge the crafts.

i set the root part on those crafts to the bottom of the fairing so i could attach them to the launcher but i never thought to move the root part back after ive merged them.

[HvP]

4 minutes ago, putnamto said:

holy crap i think this is it, i dont bother changing the root part once i merge the crafts.

i set the root part on those crafts to the bottom of the fairing so i could attach them to the launcher but i never thought to move the root part back after ive merged them.

Yea, that sounds like the culprit! Most people start with the command pod and work downwards and I'm sure MechJeb was designed with that in mind. Just use the re-root tool to root to whatever you intend to be the last pod to consume fuel and I think it should work as expected.

Happy flying!

edit: not trying to be selfish, but if you can confirm that this fixes your problem, go ahead and mark my last post as the best answer so that other people with the same problem can see how to fix it.

Edited February 26, 2018 by HvP

[putnamto]

3 minutes ago, HvP said:

Yea, that sounds like the culprit! Most people start with the command pod and work downwards and I'm sure MechJeb was designed with that in mind. Just use the re-root tool to root to whatever you intend to be the last pod to consume fuel and I think it should work as expected.

Happy flying!

well we solved the different dv totals, but that ghost stage is still their.

as an experiment i went to sandbox and just slapped a ship together and i still get the ghost stage, i went back to VAB and removed all decouplers, still get ghost stage, i removed everything from the ship accept for the command pod, and still a ghost stage, weird.

then this happened lol

[HvP]

7 minutes ago, putnamto said:

well we solved the different dv totals, but that ghost stage is still their.

as an experiment i went to sandbox and just slapped a ship together and i still get the ghost stage, i went back to VAB and removed all decouplers, still get ghost stage, i removed everything from the ship accept for the command pod, and still a ghost stage, weird.

then this happened lol

...

There's always going to be at least one stage reported in MechJeb, even if it's zero, just to at least show you that you have zero delta-v available. If you mean the one that gets added once you go to the launchpad, then it goes away as soon as you press the space button.

As for the flooded KSC... haha, nice work! It's a known bug in the Scatterer mod and seems to go away the next time you change scenes.

https://forum.kerbalspaceprogram.com/index.php?/topic/103963-wip131-scatterer-atmospheric-scattering-v00324-28012018/&page=243

Edited February 26, 2018 by HvP

[putnamto]

yeah i knew the water thing was a bug

as for the ghost stage, what i mean is that when i load just the pod onto the runway it lists two stages, im not to worried about it though, kinda curious why and how it happens though.

[sarbian]

9 hours ago, HvP said:

This may be intended behavior, I'm not sure but maybe @sarbian is already aware of this result.

The code has no way to know if the part "above" the root part is something that is intended to be dropped or not. All dv mods have the same limitation.

And the empty stage is used for engine that you toggle manually since they will burn "now" instead of when their stage is active.

 

[adsii1970]

The KSC being under water after a screen change is a well-known and well-documented issue with scatterer. It has nothing to do with MechJeb.