"Get Me Out of Here! The Lunar Module Abort Guidance System"

Julian Webb
University of the West of England

Abstract

The Abort Guidance System (AGS) comprised a gyro package and computer system (the Abort Electronics Assembly- AEA) designed to handle situations in which the Primary Guidance and Navigation System (PGNS) failed.  The task of AGS was to control the return of the LM after an abort from any point in the descent to the lunar surface, and from the lunar surface itself, to rendezvous with the CSM.  Though entirely manual aborts and ascents could, in theory, be carried out, in practice the AGS represented the last-line defence in case of PGNS failure.  Hence it needed to be highly reliable.  Though never used in a real abort situation, the AGS was highly regarded by crews. 

This paper/presentation discusses how this reliability was achieved by the use of a small, efficient general-purpose computer and guidance software allied to a simple strapdown gyro platform.  Recently available documents have given a sometimes surprising insight into the internal operation of the AEA together with its programming.  These will be discussed and compared with the Lunar Guidance Computer (LGC) forming the heart of PGNS.   

The author also intends to have available the latest version of the Lunar Module system simulator which now includes a full emulation of the AGS, together with many other features.

 

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