An 'oxygen pill' is a small pill which, when taken, allows the user to breathe and survive in various inhospitable environments, such as those with no or rarified atmosphere. An oxygen pill lasts for only a short time and must be taken regularly for an extended stay in a vacuum. Oxygen pills replaced space suits as the preferred means for facilitating Extra Vehicular Activities in space some time in the 50 years preceding the events of Fireball XL5.
Behind the Camera
The oxygen pill was conceived as a plot device which allowed the crew to avoid changing the puppets into space suits. Costume changes were time consuming as the puppet clothes had to be unstitched and then re-sewn onto the puppets.