Understanding IV & V in a safety critical and complex evolutionary environment: the NASA space shuttle program

The National Aeronautics and Space Administration is an internationally recognized leader in space science and exploration. NASA recognizes the inherent risk associated with space exploration; however, NASA makes every reasonable effort to minimize that risk. To that end for the Space Shuttle program NASA instituted a software independent verification and validation (IV&V) process in 1988 to ensure that the Shuttle and its crew are not exposed to any unnecessary risks. Using data provided by both the Shuttle software developer and the IV&V contractor, in this paper we describe the overall IV&V process as used on the Space Shuttle program and provide an analysis of the use of metrics to document and control this process. Our findings reaffirm the value of IV&V and show the impact IV&V has on multiple releases of a large complex software system.