N is nadir and points to the closest point on the Earth under the satellite. V is the velocity vector, it's the direction the satellite is heading. S is the vector pointing to the sun.
The satellite taking the picture had to slew to be pointing at Landsat-8 for a couple of frames. It is the relative positions between the satellites that changes, the vectors themselves don’t move that much in a short period of time- the nadir and velocity vectors rotate 360 degrees in one revolution around the Earth (relative to an earth center inertial reference frame). The Maxar satellite and Landsat-8 are in different orbits. It appears from the video that the Maxar satellite passed under Landsat-8, as evidenced by the nadir vector pointing straight at the screen toward the end of the video, and because we got a broadside view of the white Earth shield for the thermal imager.
