SMSI means Standard Manned Space Flight Initiator
see NSI-I in
NASA
Similar to SMSI
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
AAFM - Acoustic Atomic Force Microscopy
View all in NASA