“Timeless,” which finished its first and now the only season on NBC, was one of the more intelligent Time Travel series to have debuted last fall. The premise was that a mad man was going through time to destroy history as a way to exact revenge against a shadowy conspiracy that had murdered his family. A trio of time travelers went in hot pursuit to try to stop him, while at the same time unraveling a secret that had persisted for centuries and had affected American History in various ways. Unfortunately, NBC has decided to pass on giving the show a second season. Absent the remote possibility of another network picking up the show, “Timeless” has finished its run.

“Timeless” had iffy ratings but had developed an enthusiastic fan base, in large part because of the intriguing story lines, the characters, and the delving into historical events and people, some unknown previously to a mass audience. In one episode, our heroes team up with Ian Fleming, the author of the James Bond books, in World War II. In another, the team helps Katherine Johnson, the African American math genius whose life was depicted so admirably in the hit film “Hidden Figure,” save the Apollo 11 moon mission from disaster. The show spanned the drama, the glory, and sometimes the tragedy of American history.

Fans of science fiction have often experienced frustration at seeing their favorite shows canceled.

The classic example was the termination of “Star Trek,” ironically by NBC, after three seasons. The show went on to become a cultural phenomenon, spinning off numerous TV series and movies, creating an entire universe of people exploring the high frontier of space.

“Firefly,” another fan favorite, suffered a less kind fate.

Canceled after only part of a season, fan support led to the production of a feature-length motion picture. Nevertheless, the “space western” did not pick up enough to become a 21st Century version of “Star Trek” and thus lives on only in the memory of its fans.

The SyFy Channel was created to cater to the desires of fans of fantasy and science fiction and has achieved lots of success doing so.

Successful shows on SyFy include a dark reboot of the late 1970s space opera “Battlestar Galactica” and the current “Game of Thrones in space” series “The Expanse.” Nevertheless, mainstream networks have had a tough time sustaining good science fiction and fantasy, with some numerous exceptions. Science fiction is more expensive to produce than conventional series and tends to be canceled quicker when they don’t make the numbers immediately. That phenomenon seems to have sunk “Timeless.”