Uninteded decrease of orbit around kerbin (above 70km)

[Rebi]

Good day forum members,

I have an issue I have never heard about... My orbit of one spacecraft is getting lower, although Periapsis and Apoapsis is above 70km.

While trying to achieve a path to Minmus (I spent a lot of time to this), suddenly my spacecraft was in an orbit within the atmosphere of Kerbin and decreasing fast, which confuses me. I was trying to find any way to Minmus, which costs less fuel as possible, therefore I made some screenshots during gaming, please see attached. You can see, that within a few seconds (the time between creating the screenshots), the Apoapsis was getting from 72,797m to 72790m. Afterwards I burned up to an orbit at around 85km and the same problem appears.

I think, this should not happen and it shouldn't matter what kind of spacecraft I am using. FYI, every engine was shutted down and no RCS was activated.

So, please tell me, what is going wrong and what can I do to solve this issue.

Thanks a lot,

Regards,

Johannes

- - - Updated - - -

Unfortunately, posting the images didn't work, but that doesn't matter. I think the issue is pretty clear.

Edited January 10, 2015 by Rebi

[RainDreamer]

First: you gotta upload your images. We can't see things from your hard drive.

Second:

Does it continue to decreasing, or just fluctuate up and down? Sometimes it does that since altitude is calculated from the controlling part of the craft, I believe, so as soon as you turn your ships around with SAS, it may fluctuate a little a few meters, depending on how long your ship is.

Also, the physics engine of KSP is not very accurate and may sometimes rounding your orbit down, but that shouldn't deorbit anything as far as I know.

[GoSlash27]

It could also be a clipped part creating a phantom impulse. I've seen this happen a couple times.

Best,

-Slashy

[Rebi]

I know what you mean, but this is not the case! Nothing is fluctuating, it is continously decreasing, even on a higher orbit.

[vexx32]

We won't be able to see your pictures directly from your computer, I'm afraid. You'll need to first upload them to a file host, e.g., Imgur.

However, fluctuations of such an amount are fairly normal and will not overly affect gameplay. This is due to a combination of two causes -- one, the calculations use 32-bit floating-point numbers, which are inherently inaccurate as a result of the difficulty of storing exponents in binary (the detailed reason on that is fairly involved, even for me, but feel free to go look it up if you're curious. Be prepared to re-read things here and there, though, it can take a bit to get what's going on, sometimes!); and two, the craft's position is calculated using the root part (often a command pod) as the 'center' of the craft. As a result, rotating the craft can often result in fluctuation of the orbital display by a handful of meters.

(Yes, I'm essentially reiterating RainDreamer's points, but I like to be specific.)

[Rebi]

First of all, thanks for your answers.

You have probably already noticed that I am new in this forum and I'm not yet familiar with every option here... I can't see my original post, is this normal? I would like to delete everything related to the pictures I have mentioned. Sorry about the pictures, I was not aware that it isn't working like this. But I think you understod my problem anyway.

However, unforunatly, nothing is fluctuating. The orbit is contiunously decreasing. And it is not a small amount... a few metres in a few seconds... this means it is decreasig 2000m in half an hour.

It makes much sense if there is a phantom impulse created by a part. Can this be done by any part, or does it hase to be an engine?

Regards,

Johannes

[GoSlash27]

First of all, thanks for your answers.

You have probably already noticed that I am new in this forum and I'm not yet familiar with every option here... I can't see my original post, is this normal? I would like to delete everything related to the pictures I have mentioned. Sorry about the pictures, I was not aware that it isn't working like this. But I think you understod my problem anyway.

However, unforunatly, nothing is fluctuating. The orbit is contiunously decreasing. And it is not a small amount... a few metres in a few seconds... this means it is decreasig 2000m in half an hour.

It makes much sense if there is a phantom impulse created by a part. Can this be done by any part, or does it hase to be an engine?

Regards,

Johannes

Johannes,

It can be any part. The good news is that going to warp can cause the problem to stop. The bad news is that there is a small risk of "unplanned spontaneous disassembly", especially if warping while you cross an SOI boundary.

Good luck!

-Slashy

[skrit manfrat]

First of all, thanks for your answers.

You have probably already noticed that I am new in this forum and I'm not yet familiar with every option here... I can't see my original post, is this normal? I would like to delete everything related to the pictures I have mentioned. Sorry about the pictures, I was not aware that it isn't working like this. But I think you understod my problem anyway.

However, unforunatly, nothing is fluctuating. The orbit is contiunously decreasing. And it is not a small amount... a few metres in a few seconds... this means it is decreasig 2000m in half an hour.

It makes much sense if there is a phantom impulse created by a part. Can this be done by any part, or does it hase to be an engine?

Regards,

Johannes

it's okay, i think we understand, but a screenshot would be 1000 times more helpful.

you are 100% sure you are clear of the atmosphere while the orbit is decreasing? ( more than 70km)

it's easy to set an apo above 70km, yet still be in the atmosphere, causing your apo to decrease while in flight.

are you talking about a circularized orbit? or your initial burn?

[Starwhip]

I'd be surprised if it was a clipped part. Such a phantom drive is hard to make, let alone make it by accident.

Does your craft have any landing gear? They are particularly notorious for making phantom forces, and are, in fact, the key to phantom force drives.

If not, it could be some kind of bug that makes the game think you're still in the atmosphere/still thrusting, but I've never heard of such a thing before.

[Rebi]

OK. Thanks.

I'm sure every throttle is at zero. This was of course my first idea and I have checked this several times.

I'm using EngineerRedux-0.6.2.12 and KerbalAlarmClock_3.1.1.0.

Next thing I will do is to run Kerbal without those mods. Maybe going to warp will help as well, I haven't done this during setting nodes.

If nothing helps, I will upload this vehicle that you can test.

Cheers

[Starwhip]

Engineer and KAC shouldn't be causing that. It's weird.

Yeah, the craft upload would be a good plan. Try dropbox or mediafire if you've got it, or you can do http://tinyupload.com/. It's free and fast, if you just want to get it out as quick as possible.

[Starwhip]

Roger that.

I'll boot up my game and test out the craft the moment it gets uploaded.

EDIT:

Oi! Vexx and Sal_vager, warn me before you do that so that I don't look like I talk to myself.

Edited January 10, 2015 by Starwhip

[ROXunreal]

My orbit once decreased by a few hundred meters due to decoupling a stage in orbit. Possibly this, but if it *constantly* slowly decreases then this may not be the reason...

[Rebi]

UPDATE

to show my spacecraft and the problem I have managed to upload some pictures, see attached.

I have launched the vessel again to make some other pictures. I have now choosen a higher orbit, to see if the problem still occurs. And, yes, it is, but much less. But this doesn't matter. In my oppinion, nothing should happen, or am I wrong? In this case, I can't park a probe on an orbit of 80km. What if I have to warp a different probe for 1 year... this one wouldn't survive. Indeed, it is mor realistic, but it shouldn't be the case!

The first picture has been taken right after injection into the orbit and the second after one full orbit. As you can see the Periapsis is now 60m lower and the Apoapsis 40m higher (latest update: PE 220m lower, AP still +40m). So, this vessel would have an PE of 69000m after 200 orbits. I am sure, the values would be greater if I would be in a lower orbit. The third picture has been taken after the second orbit, which I have warped... and, compared to the first picture, not much has happened... isn't it interesting?

Ah, and btw, the orbital period is also getting faster...

Is my TWR changing because of the differents hights I have during one orbit?

I have not yet changed the configuration to test if something will be different... I will do next.

Regards,

Johannes

[vexx32]

Welp, yeah, that's a very odd one. Might want to make sure your mods are all the latest versions, in case it's an issue that's already been flagged and fixed.

And regarding the TWR, yes, the current TWR is related to the strength of gravity, which decreases the further out you are from a massive object (e.g., a planet). You should be seeing somewhat higher TWRs as your altitude increases.

[Starwhip]

Vexx said it all. Can we get a craft download? I suspect it has something to do with the OKTO near the base or the antenna on the pod, but I see no reason why they would do that.

- - - Updated - - -

Whoah, how did you mount the OKTO there? Is that an I-Beam? If it is, there could be some interesting clipping.

Still waiting for an upload, so that we can tell if it is something with your install or the craft.

[Rebi]

thanks vexx.

@starwhip: I have cheated a bit with the modular girder segment... I hope this is not causing any problems, it never had until now.

Unfortunately I won't be able to upload something in the next few hours, so don't wait for it (but please don't for get me... ;-) ).

Cheers

[Starwhip]

I won't forget you, don't worry. I'll come back later today and see what's up.

Off to test some IVA mods, then!

[GoSlash27]

UPDATE

to show my spacecraft and the problem I have managed to upload some pictures, see attached.

I have launched the vessel again to make some other pictures. I have now choosen a higher orbit, to see if the problem still occurs. And, yes, it is, but much less. But this doesn't matter. In my oppinion, nothing should happen, or am I wrong? In this case, I can't park a probe on an orbit of 80km. What if I have to warp a different probe for 1 year... this one wouldn't survive. Indeed, it is mor realistic, but it shouldn't be the case!

The first picture has been taken right after injection into the orbit and the second after one full orbit. As you can see the Periapsis is now 60m lower and the Apoapsis 40m higher (latest update: PE 220m lower, AP still +40m). So, this vessel would have an PE of 69000m after 200 orbits. I am sure, the values would be greater if I would be in a lower orbit. The third picture has been taken after the second orbit, which I have warped... and, compared to the first picture, not much has happened... isn't it interesting?

Ah, and btw, the orbital period is also getting faster...

Is my TWR changing because of the differents hights I have during one orbit?

I have not yet changed the configuration to test if something will be different... I will do next.

Regards,

Johannes

http://i.imgur.com/SPXljpb.jpg

http://i.imgur.com/pIslmqq.jpg

http://i.imgur.com/CHVDKwT.jpg

Johannes,

Yep, this is all in line with what I've seen before; warping makes it stop. Pretty sure it's a part clipping thing. I would guess it's due to that i-beam you're using to mount the okto. This is not confirmed, but I have personally seen this more frequently since the .90 update.

Could you do me a favor and try pointing the ship in the opposite direction? I'm curious to see if the behavior reverses.

Thanks,

-Slashy

[Aethon]

I can confirm the phantom force, and I'm pretty sure it's due to part clipping. It's happened to a couple of my 0.90 ships. My standard Scansat biome mapper does it. I'm pretty disappointed about it.

I mean we get these glorious new design tools ( I'm looking at you offset widget ) which allow me to poke unsightly parts into places more aesthetically pleasing, but the use of them causes spacecraft to be very hard to fly.

Couple things I do.

Get the ship where you want it and look away. Go back to the space center and leave it on rails. It'll then sit where you put it.

If you have to do something with it, do it fast and get it back on rails ASAP.

Using the lowest time warp will keep the craft on rails until you shut down the warp.

If you must be focused on the craft for a while, you may be able to use your pilot skills ( Yaaay for manned spaceflight! ) to baby sit it. Sometimes I'm able to spin the ship and reverse the effect for a while. Try all the Navball cardinal directions. It never seems to make sense which, but occasionally one direction will reverse the acceleration.

Redesign the affected ships without using the offset tool (sob).

Good luck and welcome to the Forum. Lets hope this issue is fixed down the road. ( I'm sure there is some very complicated computer programming explanation for why this is so difficult to do, but I won't really understand it when it comes. )

Edited January 10, 2015 by Aethon

[KerikBalm]

I've had stuff like this happen before, but not very noticable except on interplanetary trajectories (I abhor using part clipping, but occasionally there's a little unintentional effects), I also have stuff like this happen with some asteroid redirects, where I basically have to get the trajectory I want, then time warp and go to the space port/another craft, and not return to the asteroid until its well within the soi, and the tiny phantom force doesn't affect things much

[Rebi]

Those of you who want to test my craft can download it from the the following link (hope it is working):

http://s000.tinyupload.com/?file_id=45181572118438041047

I'm excited about your experiences!

My idea was as well, if it is a phantom force from some part, this force should always be directed into the same direction relative to the craft. Therefore I already tried to point it into several directions for a short period of time, but it made no difference. Than I was thinking: relative to Kerbal, the craft is always pointing into a different direction (if SAS is on; if it is off, the craft shall not rotate) on one orbit and the mysterious force should lift the orbit on one side of the Kerbal and lower the orbit on the other side of Kerbal... am I right? Therefore the effect should be deleting itself, but there is definitly happening something.

@Aethon: the procedure you described seems to be very annoying. But I don't want to redesign the position of the OKTO. I was very happy to get it to this location!

[Starwhip]

Right, great! Going to get right on it.

(Yep, download works fine)

[Starwhip]

Sorry for double-posting, but there's an issue.

I can't launch.

Could you save it as a different name and remove the modded parts? (I botched the .craft file by removing the Kerbal Engineer part.)

[Rebi]

Sorry for the late response.

Please download my spacecraft from the following link and test if you have the same problems with it as me.

http://s000.tinyupload.com/?file_id=95574433043516141547

Thanks a lot.

Cheers