Flight Question Orbit is sliding

[Satamanster]

Hi all.. I've been using Orbiter for sometime. I can't really say if it's a new problem or if it was always like this but I don't think so.
So what is happening Is that my orbit is sliding. I have no clue why?
I depart with the DG, get to my Apoapsis, burn to circularize, and then its as if my apoapsis is catching up with me from behind instead of me going around to catch up with it again..
Have you experienced similitar behaviour? Its the weirdest thing.
I hope you can help me.
Thank you all in advance.

 

[BrianJ]

That sounds like normal behaviour if you have "Nonspherical gravity sources" enabled in your Orbiter launchpad "Parameters" section. You can try unchecking the "Nonspherical gravity sources" box and see what happens.
More info about Nonspherical gravity orbit perturbations here:

Basics of Space Flight: Orbital Mechanics

An overview of orbital mechanics including types of orbits, mathematical formulae, and example problems.

www.braeunig.us

Cheers,
Brian

 

[STS]

Correct, those are called perturbations. A perfect-circular orbit does not exist. That is why your ApA and PeA is moving.

 

[Sbb1413]

to Orbiter Forum.

 

[N_Molson]

That's one of the main differences between Orbiter and KSP. And this apparently "erratical" behavior of orbits is how it works in real life.

Also remember : when orbiting Earth, you're not orbiting around the geometric center of a sphere that would be the Earth. You are orbiting (mostly) around the barycenter of the Earth-Moon system. That center is still well within the Earth radius (else funny things would happen on the surface !), but moves with the Moon. Ocean tides happen because sea water "reacts" to Earth's rotation and Moon relative position.

And things are actually even more complex. Depending how Earth-Moon-Sun are aligned, the intensity of the tidal forces varies. And while the pull of other planets is negligible (mostly Jupiter), its greater than 0.