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Old 10-29-2018, 02:10 AM   #1
pascal1
Orbinaut
Cool virtual orbit before liftoff

Hi,

this is my first question on this forum!
English is not my primary language, but i hope to explain everything well enough.

When using Orbiter I always thought about the 'virtual' Orbit that is shown before launch. Is it caused by the earth rotation?

I think so, that the program calculates the Orbit as if Earth would be a mass point with no extension. Am I right with these two things?

Thanks for all responses!
Pascal
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Old 10-29-2018, 08:03 AM   #2
Face
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Quote:
Originally Posted by pascal1 View Post
 English is not my primary language, but i hope to explain everything well enough.

When using Orbiter I always thought about the 'virtual' Orbit that is shown before launch. Is it caused by the earth rotation?

I think so, that the program calculates the Orbit as if Earth would be a mass point with no extension. Am I right with these two things?
to the forums.

There is a sub-forum called "International Forum" here: https://www.orbiter-forum.com/forumdisplay.php?f=66
If you have complicated questions or topics that you can only express well in your native language (it is German, right?), you can post them there.

Orbiter itself is not using only a simple point mass calculation for the orbit, but I think it does so for the orbit MFD mode calculation. I guess this is also the reason why the displayed orbit "wobbles" in flight.
I'm also pretty sure that the MFD mode has no rotational frame of reference (otherwise geostationary orbits would be mere points), so the earth rotation causes an elliptical orbit while standing still on the ground. At least if you are sufficiently near to the equator.
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Old 10-29-2018, 08:16 AM   #3
kuddel
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If you mean that highly elongated ellipse on the Orbit MFD, than it's just the orbit you would have assuming there is no (earth-)surface[1].
The orbit parameters are defined by your "altitude" (0, or roughly 6371 km from center of the earth) and your current orbital velocity (that's -as you guessed- just the earth's rotation; T=24h).
With the orbital velocity not high enough to keep you in a more circular orbit, the "virtual" orbit looks like that (high eccentricity, low orbital velocity, but the ship always at apoapsis).

[1] ...around a point-mass. Although Orbiter does more than just using a point-mass for calculations (see "non-spherical gravity" terms)

Last edited by kuddel; 10-29-2018 at 08:19 AM.
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Old 10-29-2018, 09:08 AM   #4
pascal1
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Originally Posted by Face View Post
 (it is German, right?)
Yes, you're right. Is that so clear?

I'll take a look at the international forum.

Thanks!
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