In the 1970s and 1980s this idea was refined in science fiction novels such as "Footfall" by Larry Niven and Jerry Pournelle (the same Pournelle that first proposed the idea for military use in a non-fiction context), in which aliens use a Thor-type system. During the 1980s and 1990s references to such weapons became a staple of science fiction roleplaying games such as "Traveller", "Shadowrun" and "Heavy Gear" (the latter game naming these weapons "ortillery", a portmanteau of "orbital artillery"), as well as visual media including "Babylon 5's" "mass drivers" and the film "Starship Troopers", itself an adaptation of a Heinlein novel of the same name. A smaller "crowbar" variant is mentioned in "David's Sling" by Marc Stiegler (Baen, 1988). Set in the Cold War, the story is based on the use of (relatively inexpensive) information-based "intelligent" systems to overcome an enemy's numerical advantage. The orbital kinetic bombardment system is used first to destroy the Soviet tank armies that have invaded Europe and then to take out Soviet ICBM silos prior to a nuclear strike.