NASA-Wide Software Classifications

Class A      Human-Rated Space Software Systems  

Class B      Non-Human Space-Rated Software Systems or Large-Scale Aeronautics Vehicles

Class C      Mission Support Software or Aeronautic Vehicles, or Major Engineering/Research Facility Software   

Class D      Basic Science/Engineering Design and Research and Technology Software

Class E       Design Concept, Research, Technology, and General Purpose Software   

Class F       General Purpose Computing, Business, and IT Software

Notes: It is not uncommon for a project to contain multiple systems and subsystems having different software classes.