Answer: Mae C. Jemison
In 1993, a quiet sort of history was made: a link between the fantastic space travel represented on television and real-life space travel. For the first time ever, an actual traveled-to-space astronaut appeared on the iconic TV show Star Trek. In Star Trek: The Next Generation Season 6, Episode 24 “Second Chances” (air date May 24, 1993), real-life NASA astronaut Mae C. Jemison appeared as a member of Star Fleet: Lt. Palmer.
The appearance came about thanks to a friendly connection with LeVar Burton, well-known for his role as the blind, but cybernetically-enhanced member of the crew Lt. Commander Geordi La Forge. Burton heard from a friend that Jemison loved the show and was interested in sneaking on as an extra. A few phone calls later, combined with the allure of having a real live astronaut sneak onto the ship’s roster for an episode, and a little bit of fun history was made.
An additional bit of trivia, and far more significant than a Star Trek cameo: Mae C. Jemison was the first African-American woman to travel into space (aboard the Space Shuttle Endeavour for mission STS-47 in September 1992).