Problem Periapsis lowering

[ekhidna]

Hello Everyone
I dont't know if this question should be here or in "General Questions" but since to illustrate it use the Orbit MFD I decide to put it here. First I'd like to thank you all, for this forum and your time to explain what is wrong to new people, as i consider myself a Begginer.

To the real Problem. I'm starting to use TransX and I read that to eject from Earth I should do it in Periapsis as it is when I'm moving faster as I'm near to Earth. They Also said the Recommend altitude should be 6455M .

So After I'm In Orbit I made some adjustments so that the Periapsis would be 6455M and Apoapsis just a little bit higher. So the orbit would be almost circular and Eccentricity almost null.

As you can see in my first image I started with a bad Orbit with a big Apoapsis and low Periapsis. Orbit1.jpg
Then at Perispasis I Burned to Lower my Apoapsis. Orbit2.jpg
Then after 2 more Burns I could maKe the Orbit with a Periapsis of 6.455M,
and an Apoapsis of 6.597M.
The Problem is if I dont't do anything and continue simply orbiting my Periapsis starts to move down. And with this i don't mean after a while, it starts very soon in fact in the 1st orbit the Periapsis keeps falling.
Do you think with this images you can explain this to me? Or do you need more data?
Thank you in advance.
João Oliveira

 

[meson800]

So After I'm In Orbit I made some adjustments so that the Periapsis would be 6455M and Apoapsis just a little bit higher. So the orbit would be almost circular and Eccentricity almost null.
The Problem is if I dont't do anything and continue simply orbiting my Periapsis starts to move down. And with this i don't mean after a while, it starts very soon in fact in the 1st orbit the Periapsis keeps falling.

You are in the atmosphere, and atmospheric drag is pulling you down.

To the real Problem. I'm starting to use TransX and I read that to eject from Earth I should do it in Periapsis as it is when I'm moving faster as I'm near to Earth. They Also said the Recommend altitude should be 6455M .

By default, Orbiter MFD displays radius, not altitude. I believe the second button down from the right switches it from radius to altitude display.

You can tell, because the perapsis is listed as PeR when in radius mode, and PeA in altitude mode.

Because the radius is measured from the center of Earth, you have a smaller distance.

 

[ekhidna]

Hmmm, so I mixed the things in Orbit MFD, and I'm showing data the wrong way, mixing Altitude with Distance from Earth Center.
I think I got it in theory, I must change the display to read correct data as I'm very low.

Let's see in practice how it will do.

Thank you Meson

 

[Urwumpe]

What you should consider in your theory: Orbiters Orbit MFD does not display you the true orbit parameters (which are way more complex), but so called osculated elements, which show you a Kepler orbit based on the current radius vector and velocity vector.

The difference is, that the osculated elements are not taking exosphere drag, Non-spherical gravity or other gravity bodies in account, the displayed parameters can vary a lot if you are having strong influences by such sources.