"Flying With an Elephant on Your Back: Apollo 13 and the Digital Autopilot"

Frank O'Brien

Apollo historian for NASA (volunteer)
Researcher, Apollo Lunar Surface Journal and Co-editor of the Apollo Flight Journal
Lunar Module Simulator preparation, Cradle of Aviation Museum
Associate Director at the Infoage Science and Learning Center.


Attitude control of the Apollo Spacecraft was performed by the digital autopilot. routines of the Apollo Guidance Computer. The DAP's task was complicated by the need to maneuver or maintain attitude under several different spacecraft configurations and significantl changes in mass. In this talk, we will introduce the Apollo DAP, its interfaces and control laws with emphasis on the Lunar Module. Finally, we will address the problem of controlling the CSM/LM stack from the Lunar Module, which was necessary on Apollo 13.


Frank O'Brien is an editor of the Apollo Lunar Surface Journal and Apollo Flight Journal. He has written extensively on the Apollo missions, with emphasis on the guidance computer. He is the space historian at the Infoage Science/History Learning Center in Wall, NJ


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