Use of quaternions in Shuttle guidance, navigation, and control

An attempt is made to show how quaternions can be used. It is noted that the quaternion caught on rather quickly when the software was faced with both a 'core' and 'CPU' scrub. It was at this point in the Shuttle program that all disciplines seriously considered using quaternions to perform the guidance, navigation, and control functions required to support mission objectives. A review of today's software requirements shows that the quaternion found a home in nearly all principal functions in the Space Shuttle software. These uses are discussed here from a practical viewpoint, with no attempt made to rigorously derive the applications discussed. Where applicable, the quaternion algebra or technique is expanded upon to illustrate the simplification or approximation used in the Shuttle program.