Just to drop in a note on Ralph's behalf - while many of us grew up thinking of everything in the painting as his design, Ralph would be quick to point out that the X-Wing was Joe Johnston's concept. As was the TIE Fighter, and even the Death Star surface detail concepts in this particular production painting. Ralph was taking the diverse design concepts George had chosen (in this case Joe's) and incorporating them into a dynamic setting to serve as inspiration to the rest of the crew who were tasked with realizing these images in three dimensions.
While Ralph certainly had his share of designs brought to life in the films, he was not the only person contributing amazing work.
John Scoleri
co-author
The Art of Ralph McQuarrie