techniques; a ray gun might require a pyrotechnic during filming, and then an optical glowing line added to the film image in post-production. Stunts are another important category of physical effects. In general, all kinds of special effects must be carefully planned during pre-production. Computer-generated imagery Babylon 5 was the first series to use computer-generated imagery, or "CGI", for all exterior space scenes, even those with characters in space suits. The technology has made this more practical, so that today models are rarely used. In the 1990s, CGI required expensive processors and customized applications, but by the 2000s (decade), computing power has pushed capabilities down to personal laptops running a wide array of software. Models and puppets Models have been an essential tool in science fiction television since the beginning, when Buck Rogers took flight in spark-scattering spaceships wheeling across a matte backdrop sky. The original Star Trek required a staggering array of models; the USS Enterprise had to be built in several different scales for different needs. Models fell out of use in filming in the 1990s as CGI became more affordable and practical, but even today, designers sometimes construct scale models which are then digitized for use in animation software. Models of characters are puppets. Gerry Anderson created a series of shows using puppets living in a universe of models and miniature sets, notably Thunderbirds. ALF depicted an alien living in a family, while Farscape included two puppets as regular characters. In Stargate SG-1, the Asgard characters are puppets in scenes where they are sitting, standing, or lying down. In Mystery Science Theater 3000, the characters of Crow T. Robot and Tom Servo, two of the show's main (and most iconic) characters, are puppets constructed from random household items. Animation As animation is completely free of the constraints of gravity, momentum, and physical reality, it is an ideal technique for science fiction and fantasy on television. In a sense, virtually all animated series allow characters and objects to perform in unrealistic ways, so they are almost all considered to fit within the broadest category of speculative fiction (in the context of awards, criticism, marketing, etc.) The artistic affinity of animation to comic books has led to a large amount of superhero-themed animation, much of this adapted from comics series, while the impossible characters and settings allowed in animation made this a preferred medium for both fantasy and for