Evolution of velocity fluctuations in the fast wind stream. Measured vector components of the proton velocity measured by Parker (magenta), Solar Orbiter (lime), and Wind (red) are displayed in various combinations. Left column: V_R versus V_T (top) and V_N (bottom) are displayed for all three spacecraft measurements, with their respective “Alfvén spheres” overlaid as dashed circles. Solid crosshairs indicate the centroid of each sphere, which is interpreted to be the stream’s de Hoffman–Teller velocity. Right column: corresponding plots of V_N versus V_T, showing the projection of the fluctuations perpendicular to the radial direction. These are separated by spacecraft from top to bottom, avoiding overlap of the data points, with all three Alfvén sphere projections displayed in each case. In the top right panel, gray shading indicates the region of velocity space outside the SPAN-i FOV at this time and is observed to accurately correspond to the apparent diagonal cutoff in the Parker V_N–V_T data (magenta).