AK20 means 80% nitric acid + 20% N2O4
AK = Azotna Kislota = Nitric Acid in
NASA
Similar to AK20
AA - Adverse Action
AA - Antenna Assembly
AAA - Avionics Air Assembly
AAC - Aft Access Closure
AACB - Aeronautics and Astronautics Coordinating Board
AAD - Attitude Anomaly Detector
AAFE - AeroAssist Flight Experiment
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