XO means X-axis of Orbiter Orbiter structural body reference in NASA
Similar to XO
ACC - Aft Cargo CarrierACCA - Automatic Cloud Cover Assessment
ACCMS - Advanced Checkout, Control, and Maintenance System
ACCS - Advanced Checkout and Control System
ACE - Advanced Composition Explorer
ACE - Apollo Checkout Equipment
ACES - Acoustic Containerless Experiment System
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