During a countdown to a spacecraft launch, a delay purposely added in advance. Two-day countdowns can have up to seven built-in holds to give the inspection crews a rest. These can last from 10 minutes to about 26 hours. Built-in holds are also added to assess the weather. A launch of the space shuttle Discovery on 7 November 1984 was postponed during a built-in hold due to rough upper-atmosphere conditions.
Subjects: Astronomy and Astrophysics.