Orientation During Flight 

NASA describe 2 orientations for ISS called XPOP ( X-axis Perpendicular to Orbital Plane ) and XVV ( X-axis towards Velocity Vector ). The x-axis is the line through Destiny, Unity, Zvezda and Zarya. As the ISS orbit moves round the Earth the station alternates between the two modes in order to allow good alignment between the main solar panels and the Sun. For more information see the Space Station User's Guide

These two screen shots are taken from my ISS Simulator program, illustrate the 2 flight modes:

In XVV mode the ISS flies like an aeroplane with the main panels as wings and Destiny at the front. In the image it will fly away from the viewer along the green line which represents its orbit.	In XPOP mode the line from Destiny to Zvezda is perpendicular to the orbital plane. In this view the ISS will fly away from the viewer along the green orbit line.

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