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.