“Space” became The X-Files season 1's most expensive episode. Its costs rose when production overruns affected the construction of the Mission Control set.
The episode was designed as a relatively economical bottle episode, a story using limited locations and a contained cast. It also relied heavily on inexpensive stock footage from NASA, which seemed suited to its plot about the Space Shuttle program and an apparent extraterrestrial presence.
The planned savings were undermined by the Mission Control set. Construction costs exceeded expectations, turning “Space” into the season's costliest episode despite its intended low-budget format. This is why the answer is not an episode such as “E.B.E.,” “Fire,” or “Ice.”
“Space” was written by series creator Chris Carter and directed by William Graham. Carter drew inspiration from reports about the so-called face on Mars, a famous example of pareidolia involving a formation in the Cydonia region. The episode aired on November 12, 1993, and was a standalone monster-of-the-week story rather than part of the season's central mythology.