Very nice, a really detailed mesh!
As you removed the materials, and now it works, indicates that the original mesh maybe had multi-materials. Unfortunately Orbiter does not support multi-materials, so it is necessary to assign each individual mesh a single material.
Two words on the mesh orientation:
As per Orbiter default, the mesh should be oriented so its longitudinal axis is the z-axis. Currently it is the x-axis, which makes it flying 'sideways'.
And I suggest to translate the mesh a little in longitudinal axis, so that the origin of the coordinate system is in the center of the model. Currently it is in the center of the orbital module. Orbiter's camera looks on the origin of the mesh, and also the ship rotates around this point when maneuvering.
Have fun with your model becoming an addon! :thumbup: