I'm looking for a mouse orbit script that satisfy this request:
Playing with the standard mouse orbit I met the limit of the Y axis, when I'm on the top of the target the camera spin around, you can see what I mean in the shot below:
What I want is a different behavior, as show in the next screenshot:
How can I modify the mouse orbit script to achieve that?
You could try modifying the camera's local transform to balance out its regualr transform so that you still have regular control over it regardless of what degree it's turned to.
Parent your camera to an empty gameobject in the middle of your planet, and rotate that gameobject's transform whenever you press the corresponding button.
This way the camera will rotate along with your empty game object.
Say: when you press your UP arrow, you'll want to have the parent gameobject rotate over it's Y axis.