craft loses alignment

[Sigma88]

issue:

Once achieved orbit with a craft, if the orbit is not high enough the craft will not maintain it's orientation in space.

If the orbit is high enough the issue does not present itself.

how to reproduce:

1 - take any craft to a 78km orbit around kerbin in KSP 1.0.4

2 - make it a equatorial orbit with as little eccentricity as possible

3 - point the craft to the sun

4 - time warp in order to complete a full orbit around kerbin

5 - the craft is no longer pointing to the sun

control:

6 - raise the orbit to 200 km

7 - repeat from point 3 and 4

8 - the craft is still pointing to the sun

The only difference I could find between the two orbits is that at 200km you can't see the real kerbin surface, you only see the texture you see from the tracking station.

any ideas?

[sal_vager]

Hi Sigma, please enable SAS on any vessel that you require to point in one direction, but be aware that floating point errors will always creep in, with a greater or lesser severity depending on your vessels distance from the current origin.

[Sigma88]

hi sal,

are you saying that floating point errors can make a craft spin during timewarp? in just one orbit around kerbin at 78km?

and this error would get smaller the farther I get from kerbin, because at 200km there's no sign of spinning at all.

edit

this is what I see:

the two screenshot were taken few seconds one from the other, time warp 50x was never turned off

first screenshot (time is 3d 5h 53m 04s)

second screenshot (time is 4d 0h 1m 23s)

game time between screenshots = 8m 19s

IRL time between screenshots = 10 seconds

it seems a bit extreme to be just floating point error, but I'm not an expert so if you are sure I'll trust you.

I just wanted to be clear on what I see

thanks for your answer

Edited July 12, 2015 by Sigma88

[Claw]

How far off is the angle? (any pictures?) It might be floating point, as Sal points out. Possibly it could be something else. There are a few other odd quirks that also result in craft not pointing the correct direction from time to time (like the occasional quickload).

Cheers,

~Claw

[Sigma88]

I've added a more detailed description with screenshots in my previous post.

Let me know if you need more info

[sal_vager]

Uh, okay I may be wrong here but your craft is still pointing in the same direction, it'll be held facing an absolute heading, not facing what you're pointing at, and you're orbiting kerbin.

But Kerbin is also in orbit around the sun, so each day it'll move a bit in its orbit.

Try pointing at a background star and see if there's any change.

Derp no I see the stars move to, nevermind.

Edited July 12, 2015 by sal_vager

[Sigma88]

Well, it is 8 minutes.

With the skybox I have the same problem, ill upload screens asap

Btw, at higher orbits (200km) the problem does not appear

Edited July 12, 2015 by Sigma88

[sal_vager]

What addons have you installed?

[Sigma88]

I've tried with a clean 1.0.4 copy of a virgin steam ksp folder

Only addon hyperedit.

I've also tried without Hyper edit but it's a pain getting the right orbit

btw, if you switch back and forth between the screenshots I posted earlier it's clear that the skybox moves.

the camera was in "Locked" mode, so it didn't move relative to the craft

- - - Updated - - -

here's another couple of screens

I started timewarping before taking the first screen, after a couple of seconds (real life) of time warp I took the first screenshot

link

then I waited 3 seconds and took the second screenshot

link

you can see how the blue star on top of the tail fin is definitely moving

edit, ok now the links are correct

Edited July 12, 2015 by Sigma88

[Claw]

Okay. I see what you're talking about. It looks like there's an internal frame of reference shift at 100km. Actually, this might explain some other behavior that I see in other areas.

In either case, it looks like you're correct. You can see the cutoff if you set an elliptical orbit with PE below 100km, and AP above 100km. Then set your rocket pointing at the sun as you did in the pics.

Nice find.

Cheers,

~Claw

[Sigma88]

happy to help

is this something fixable? It's not like it's a major issue. I noticed it just by chance

thanks for taking the time

Sigma

[sal_vager]

Probably not fixable by us, but by the developers, though I bet it'd be a pain to ensure everything was perfectly lined up, it may be considered too minor to deal with though.

If you'd like, head on over to the bug tracker and write this up as a new issue, it'll ask for your details but you can use a fake name.

[Sigma88]

Probably not fixable by us, but by the developers, though I bet it'd be a pain to ensure everything was perfectly lined up, it may be considered too minor to deal with though.

If you'd like, head on over to the bug tracker and write this up as a new issue, it'll ask for your details but you can use a fake name.

Oh, I didn't know there was a bug tracker.

thanks