Ronpur is specifically a pretty big fan of the alternate Apollo programme and earlier Mars spaceflight programme seen in Stephen Baxter's 1996 alternate history novel Voyage. Many of the alternate spaceflight artworks made by Ronpur illustrate various scenes and events in the novel and further extrapolate the novel's alternate timeline. They might be some of the best Voyage-related fan art you'll ever see anywhere on the Internet. Take a look. (Page 154 in particular.)
He is not to be confused with the banned member Rognvald, who had a somewhat similar-sounding username.