Aerobraking lifts Ap? Bug?!?

[kurja]

From the images OP posted it looks like atmosphere actually do slow you down as the specific angular momentum is going down. (The 26m increase in Ap is much less energy gained than the loss of 3m at Pe).

I think the Ap going up is just a rounding error. And as numerobis points out the orbit should decay after many passes.

I wrote here earlier that both Pe and Ap would rise, seems like I got that wrong and Pe actually did drop by 3 meters.

At the same time, Ap rose 26 kilometers, which is not the whole truth as the first screenshot is from after Pe, total change was greater. Intuitively that makes no sense to me but maybe someone with a better grasp of these numbers can tell whether or not energy is increasing.

I did make that pass a couple times, and saw the same thing happen each time. I guess that if my Pe kept dropping a few meters at a time I eventually would have gotten enough braking to bring Ap down... unless my Ap had reached escape by then

[Jasmir]

So I went to Eve and aerobraked to get captured, then raised my Pe a bit higher so I could do another aerobraking pass without ending up on Eve and maybe go to Gilly... But, when I touch the atmosphere my Ap is rising??? What's going on, has anyone else seen this happen?!?

If you not decouple/eject something and don't played around with RCS/Throttle/etc... something went wrong. But i've never seen such a behavior on my side.

[kurja]

No, I was just letting it fly on it's own. Ap was climbing steadily as long as I was in contact with the atmosphere.

[Nao]

I wrote here earlier that both Pe and Ap would rise, seems like I got that wrong and Pe actually did drop by 3 meters.

At the same time, Ap rose 26 kilometers, which is not the whole truth as the first screenshot is from after Pe, total change was greater. Intuitively that makes no sense to me but maybe someone with a better grasp of these numbers can tell whether or not energy is increasing.

I did make that pass a couple times, and saw the same thing happen each time. I guess that if my Pe kept dropping a few meters at a time I eventually would have gotten enough braking to bring Ap down... unless my Ap had reached escape by then

Lol, welp thats a second miss in one thread gotta stop posting for today, sorry!

Although I do remember Eve's atmosphere right at the edge of space being wonky some patches ago and then it got "fixed" a patch later. So maybe there are still glitches or that's a leftover from some kind of a fix.

[numerobis]

Same happens with Kerbin, in my experience -- Eve and Kerbin are where I've noticed the same behaviour. I wouldn't be surprised it happened in all atmospheres.

I have had this when running out of fuel coming back from Mun; after many, many passes, finally Pe fell enough and I started losing energy, and eventually I landed. But it's true I suppose that this glitch could theoretically send you sailing out to a solar orbit!

I'm not sure how to exploit this bug... Because that's what we should do with it, obviously!

[tetryds]

what about the phantom forces caused by control surfaces?

any movement on the atmosphere can speed up the ship then

[kurja]

what about the phantom forces caused by control surfaces?

any movement on the atmosphere can speed up the ship then

no control surfaces on the ship

[ferram4]

Alright, so what does this ship look like? (read: post a picture) Are there any physics-less parts (cubic octagonal struts, landing gear, etc.) on it? Do you have trim set by accident?

Are you using any mods besides Engineer?

[allmhuran]

I can confirm that this effect can is seen at Eve in vanilla KSP, no trim, no physics warp, no control surfaces. It doesn't appear to be a rounding error, apoapsis consistently increases while periapsis slowly decreases. The ship I used did have physics-less parts. One thing I did not try was firing up the engines for very tiny retrograde thrust while it was happening to see if that magnified or reduced the effect.

[BubbaWilkins]

I believe what you are seeing is that gravity and atmospheric losses are combining in such a manner as to shape the orbit in a more parabolic arc around the PE. This forces the AP further out, but makes the orbit more oblong and and the overall orbital path shorter in the same process.

[saskwach]

I'm hitting this too, and it looks an awful lot like a bug. As I hit the upper atmosphere, my apoapsis increases steadily. I have a save of it; if anyone knows which files to zip up, I can put them on a server somewhere.

Here's a picture of the ship:

Edited February 13, 2014 by saskwach

[Skorpychan]

Slingshot effect. I've done similar on Kerbin; I went from a high orbit after a Mun escape, to about 20k kerbin periapsis, to an escape trajectory. Projected, anyway. Once I hit atmosphere, speed bled off shockingly fast.

[saskwach]

Slingshot effect. I've done similar on Kerbin; I went from a high orbit after a Mun escape, to about 20k kerbin periapsis, to an escape trajectory. Projected, anyway. Once I hit atmosphere, speed bled off shockingly fast.

That's not how gravity assists work. There's no SOI change involved. This is a bug where hitting the outermost part of Eve's atmosphere increases the amount of orbital energy the ship has.

[Greenspan]

Does the Ap increase ONLY when you are in the atmosphere? (i.e. Ship alt < 96708m) Or does it begin before/continue after entering/exiting the atmosphere? Even for a few seconds?

[saskwach]

Does the Ap increase ONLY when you are in the atmosphere? (i.e. Ship alt < 96708m) Or does it begin before/continue after entering/exiting the atmosphere? Even for a few seconds?

I only see it in the atmosphere. The orbit seems stable otherwise.

[iBeej]

Quick question...

Were you performing any burns at all? Is the Ap increasing with throttle killed?

The reason I ask, is I have been caught off guard with side thrusters mounted upside down and burning retrograde on the navball is actually burning prograde. Which would increase Ap.

And can you confirm that ALL thrusters are mounted in the same orientation?

[rhoark]

If the minor axis is small enough, the lowest altitude doesn't have to correspond with the local minimum of speed. Then the distribution of drag over time would be bimodal. The cumulative effect would be asymmetrical, since it would go into the second hump with slightly less speed.

[saskwach]

I can confirm that the only thruster (ion engine) was off, and it's oriented pointing aft. My orbit was less eccentric than the pictures the OP put up. Apoapsis was around 500km (and climbing) with periapsis just inside the atmosphere.

Edited February 14, 2014 by saskwach

[numerobis]

I've since also seen this at Laythe, by the way. Trying it at Duna and Jool would round out the "all atmospheres" question.