This is an original cover illustration for Ben Bova's "Star Watchmen" series - two novels in one,  both "The Star Watchmen" and "The Dueling Machine" published by Baen, 1994.  Classic SF cover by DKS,  handpainted in acrylic on gypsum board, 24" x 16"  and signed (see back, with title for one of the two novels that Baen decided to combine into one anthology book.