SMSI means Standard Manned Space Flight Initiator
see NSI-I in
NASA
Similar to SMSI
AA - Astronomical Applications
AA - Adverse Action
AA - Antenna Assembly
AAA - Avionics Air Assembly
AAC - Aft Access Closure
AACB - Aeronautics and Astronautics Coordinating Board
AAD - Attitude Anomaly Detector
View all in NASA