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Old 12-25-2016, 08:34 PM   #1
indy91
Orbinaut
Default Shape of the Earth and Earth atmosphere in Orbiter 2016

Orbiter 2016 introduced terrain to Orbiter. However, it seems the me that the basic shape of the Earth is still spherical. It doesn't matter if I put a Deltaglider at Cape Canaveral, the equator or the North Pole. In every case the radius is the radius as defined in the Earth config file, which is 6371.01 km, the mean radius of the Earth.

The basic shape of the actual Earth is an ellipsoid with a polar radius of 6,356.8 km and an equatorial radius of 6,378.1 km. When I first heard about the terrain in Orbiter 2016 I was sure the Earth would finally get the correct shape. But that doesn't seem to be the case.

So my question is then, are there any plans to adjust the shape of the Earth in Orbiter or are there some difficulties to it that didn't allow the shape to be fixed with the introduction of the terrain? And a basically identical question, will the atmospheric model one day be adjusted for the ellipsoid shape?

The reason I ask is for the next version of NASSP, which will be Orbiter 2016 compatible. There are a few programs in the emulated AGC that assume the ellipsoid Earth. So navigation measurements with the sextant for Earth horizon/star aren't very accurate, if you try to measure the horizon of the Earth. Also the point of entry interface is fixed at 400,000 feet. And this altitude is also used for a few onboard calculations as an altitude above the Earth ellipsoid, instead of the spherical approximation.

Our solution to this for NASSP 7.0, the current version, was setting the Earth radius in the config to the radius at Cape Canaveral. That way the actual launch position vector is fairly realistic and it's not too far away from the mean radius, so the errors are not as big at the equator and the poles.
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