Answer: Mae C. Jemison
In 1993, a quiet type of history was made: a link between the amazing space travel represented on television and real-life space. For the first time ever, a real journey-to-space astronaut appeared on the iconic TV series Star Trek . In Star Trek: The Next Generation Season 6, Section 24 “Second Chances” (air date May 24, 1993), NASA astronaut Mae C. Jemison appeared as a member of Star Fleet: Lt. Palmer.
The appearance took place thanks to a friendly connection to LeVar Burton, well known for his role as the blind, but cybernetically improved member of the crew Lt Commander Geordi La Forge. Burton heard from a friend that Jemison loved the show and was interested in sneaking in as an extra. A few phone calls later, combined with the allure of having a real live astronaut sneak onto the ship's list for a section, and some fun history was made.
Another piece of trivia, and much more significant than a Star Trek cameo: Mae C. Jemison was the first African American woman to travel into space (aboard the space shuttle Endeavor for mission STS-47 in September 1992).