The AS Thanatos is a mentioned-only spacecraft.
The Thanatos was an abandoned Simulant attack ship, looted by the boys from the Dwarf during which they found the Casket of Cronus. This was later sought by the Expanoids to achieve their greater plans, but they got there too late.
However the Expanoids were able to locate Starbug and barter the return of the Casket. This in turn led to the creation of the alternate Earth called "Twentica", ruled over by the Expanoids, although the Dwarfers were eventually able to undo the actions of the Expanoids. (Twentica, Series XI)