Fig. 2.

(a) Image of a NASA astronaut wearing the space suit helmet. The helmet’s protective and inside visors can clearly be observed. (b, c) Calculated radii of curvature (in mm) for different locations on the front surface of the (b) protective and (c) inside visors of the space suit helmet (when looking head-on at the helmet). Approximate distances from the center of the visor to each measured location are indicated in italicized font. The inside visor was smaller than the protective visor. Dashed lines indicate location of vertical slices used in subsequent cross-sectional figures, Zemax modeling and calculations.