Problem Is this a bug? Apoapsis and periapsis changing on their own

[DrEStrangelove]

I am still a beginner, but I can get XR2 to ISS and dock by now. Sometimes, however, I’m encountering some anomalies. In my last attempt, I adjusted my apoapsis to catch up to ISS, it placed it quite close to periapsis - about 366k and 357k. When I tried to raise it back, I noticed that something odd happened, at least with the MFD - about 20-30 seconds from periapsis or apoapsis, the counter would start going up for no apparent reason, as would my altitude, so that I would never reach periapsis or apoapsis. I’ve never noticed this one before and I don’t think it’s supposed to happen. I have all perturbations on so maybe that’s the reason somehow? But why would it only happen now and not on 30 or so other flights.

 

[Buck Rogers]

Is this the same problem as your last question?
You say your altitude is changing, is your apo and/or peri changing drastically as well?

It may help to detail Orbiter version, addons etc...

I don't think it has to do wih perturbations

 

[DrEStrangelove]

Is this the same problem as your last question?
You say your altitude is changing, is your apo and/or peri changing drastically as well?

It may help to detail Orbiter version, addons etc...

I don't think it has to do wih perturbations

It’s different. That issue was about both periapsis and apoapsis rising endlessly with no thrust, and it would occur every time. This one only happened once so far and both periapsis and apoapsis are simply unachievable - the timer would start rising right before them and then reset.

I’m using the latest Orbiter 2016 from the main site, with XR2 and hi res textures. I just installed them, together with the new elevation .tree.

 

[Buck Rogers]

Does sound strange?
If you can reproduce it maybe post a scn. file and someone can check it (unfortuneatly the XR series doesn't work on 32bit systems so I can't).

 

[CTarana45]

Does sound strange?
If you can reproduce it maybe post a scn. file and someone can check it (unfortuneatly the XR series doesn't work on 32bit systems so I can't).

XR series does work on 32 bit computers!

Thanks, Guys!

Christopher Tarana

 

[Buck Rogers]

O.K. I knew I should have clarified!- They don't work in Orbiter2016 with 32bit.
And I can test your scn. file (Just post it between code marks) but I'd have to swap the XR for something else, as long as the bug is not XR related (which is IMO very unlikely, the XR series has always run very smoothely in my experience) it should be noticable (if reproducable).
Often it's a case of a conflict between addons/ plugins but that appears not to be the problem in this case.
What I can do is run the scenario and tell you if it works my end

 

[dbeachy1]

To clarify, XR vessels, and Orbiter 2016, are all 32-bit code. I think what you mean is that XR vessels require Windows Vista or newer, and thus cannot run on Windows XP. But XR vessels run just fine on 32-bit versions of Windows Vista, Windows 7, Windows 8, and Windows 10.

As for the issue here, it does sound like something is providing thrust when it shouldn't.

 

[STS]

I am still a beginner, but I can get XR2 to ISS and dock by now. Sometimes, however, I’m encountering some anomalies. In my last attempt, I adjusted my apoapsis to catch up to ISS, it placed it quite close to periapsis - about 366k and 357k. When I tried to raise it back, I noticed that something odd happened, at least with the MFD - about 20-30 seconds from periapsis or apoapsis, the counter would start going up for no apparent reason, as would my altitude, so that I would never reach periapsis or apoapsis. I’ve never noticed this one before and I don’t think it’s supposed to happen. I have all perturbations on so maybe that’s the reason somehow? But why would it only happen now and not on 30 or so other flights.

Have you got Nonspherical gravity sources enabled under Parameters on the orbiter launchpad? If that is the case, the behaviour is perfectly normal: Orbital perturbations.

 

[DrEStrangelove]

Have you got Nonspherical gravity sources enabled under Parameters on the orbiter launchpad? If that is the case, the behaviour is perfectly normal: Orbital perturbations.

I do, but I’ve never noticed anything like that before, with the exact same scenario flown in the same way. Why and how would that happen this time?

 

[Urwumpe]

I do, but I’ve never noticed anything like that before, with the exact same scenario flown in the same way. Why and how would that happen this time?

Do you use a throttle controller for input?

 

[DrEStrangelove]

Do you use a throttle controller for input?

I do, but I usually unplug it after reaching space. I didn't this time, though.


Also, I tried reloading the game and the issue disappeared, which baffles me - the old issue I had would persist no matter what.

 

[Urwumpe]

I do, but I usually unplug it after reaching space. I didn't this time, though.

Might be an explanation, if the throttle does not have a large enough deadband for "cutoff", it will send sporadically something like "0.5% thrust" to orbiter, producing a tiny, almost unnoticable thrust. You should notice a small mass flow then, if you disable RCS completely and just coast.

Oh, and disable the APU for the XRs of course, if you don't need them. Their exhaust might be propulsive, if my memory is not completely wrong.

 

[DrEStrangelove]

Might be an explanation, if the throttle does not have a large enough deadband for "cutoff", it will send sporadically something like "0.5% thrust" to orbiter, producing a tiny, almost unnoticable thrust. You should notice a small mass flow then, if you disable RCS completely and just coast.

Oh, and disable the APU for the XRs of course, if you don't need them. Their exhaust might be propulsive, if my memory is not completely wrong.

I have a sizable deadband, so this shouldn't be an issue, and second - why would it only occur just before reaching periapsis/apoapsis? If I had a tiny thrust going throughout the orbit, I would have noticed it in between.

I had no idea that APU's exhaust may be propulsive. I'm sure it was off at that time, but I'll keep that in mind!

 

[Urwumpe]

I have a sizable deadband, so this shouldn't be an issue, and second - why would it only occur just before reaching periapsis/apoapsis? If I had a tiny thrust going throughout the orbit, I would have noticed it in between.

I had no idea that APU's exhaust may be propulsive. I'm sure it was off at that time, but I'll keep that in mind!

Well, it depends on the direction in which you are accelerating. If altitude increases (And I am sure it does), this means that you have a force accelerating you away from Earth. This could be from outside, like sun, moon or even Jupiter. But those are weak and only cause a small change in altitude, a few meters. Also they are periodic, they are neutralized again in the second half of the orbit.



Some perturbations are more noticable around the apsis, others around the nodes.

 

[DrEStrangelove]

Looks like something happened again. My time to reach periapsis keeps rising, while the actual periapsis doesn't change, altitude keeps slowly dropping and everything seems to be just fine. This continues for a while, then both my apoapsis and periapsis rise, and then everything continues to drop again. Then, when I'm close to periapsis or apoapsis, they suddenly rise, so I can never reach them.

Here's the link to the current state of the scenario: https://easyupload.io/g54a0o

 

[Urwumpe]

Looks like something happened again. My time to reach periapsis keeps rising, while the actual periapsis doesn't change, altitude keeps slowly dropping and everything seems to be just fine. This continues for a while, then both my apoapsis and periapsis rise, and then everything continues to drop again. Then, when I'm close to periapsis or apoapsis, they suddenly rise, so I can never reach them.

Here's the link to the current state of the scenario: https://easyupload.io/g54a0o

Ah - maybe you just discovered why Orbit MFD writes "Osculating orbital elements" as warning on top. :lol:


https://en.wikipedia.org/wiki/Osculating_orbit


I thought you mean rapid secular (non-period) change.

 

[DrEStrangelove]

Rapid change occured before, but it went away after reinstalling it, I was afraid this might be a variation of that bug again.

Good to know it’s intentional, I assumed that something must be wrong with the MFD - seeing time to periapsis change a lot while periapsis itself barely changed.

 

[DaveS]

Rapid change occured before, but it went away after reinstalling it, I was afraid this might be a variation of that bug again.

Good to know it’s intentional, I assumed that something must be wrong with the MFD - seeing time to periapsis change a lot while periapsis itself barely changed.

What you might want to disable is "Nonspherical gravity sources" on the Parameters tab.

 

[Urwumpe]

Rapid change occured before, but it went away after reinstalling it, I was afraid this might be a variation of that bug again.

Good to know it’s intentional, I assumed that something must be wrong with the MFD - seeing time to periapsis change a lot while periapsis itself barely changed.

No, it is just the way how the data is displayed - instead of calculating a real and non-kepler orbit, or a filtered orbit with proper elements, it displays the Kepler orbit passing through your current position with your current velocity vector.



That is much more CPU friendly, but of course, requires some understanding of the data displayed (you essentially are required to do the filtering in your brain, what works pretty good usually with some experience) and to use a more careful approach to maneuvering.



Instead of a single hail mary maneuver, you carefully approach the target - and the closer you get, you and the target will get more similar osculating elements, with the differences to the real orbits becoming similar as well (Since you and the target are subject to the same perturbations, if you would be in the same position at the same time, after all. And you will get almost the same perturbations, if you would just be at the same position as the target at a slightly different time, like 30 minutes later)

---------- Post added at 22:38 ---------- Previous post was at 22:34 ----------

What you might want to disable is "Nonspherical gravity sources" on the Parameters tab.

Does not change much, since sun and moon are also producing differences between an osculating kepler orbit and the real orbit.



The behaviour will just get much weaker close to Earth.

 

[dbeachy1]

Oh, and disable the APU for the XRs of course, if you don't need them. Their exhaust might be propulsive, if my memory is not completely wrong.

Just to set the record straight, there is no exhaust at all for XR APUs (i.e., there is no "APU thruster" or anything like that). Running the APU does reduce your total mass (very) slightly as it runs and burns the fuel, but that's all. :tiphat: