The launching bay was an area of the Ark.
The bay was used to eject waste matter, including bodies, into space. The punishment intended for the First Doctor, Steven Taylor and Dodo Chaplet at their trial was to be ejected from the bay into space.
The Monoid statue was ejected through the bay to stop the bomb in it from destroying the Ark. Its great weight meant that a Refusian had to carry it to the bay. It exploded shortly after ejection. (TV: The Ark)