An Assessment of Space Shuttle Flight Software Development Processes (1993) / Chapter Skim
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4. The Space Shuttle Flight Software Verification and Validation Process
4. The Space Shuttle Flight Software Verification and Validation Process
Pages 51-60
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From page 53... ...
As promised in the Interim Report, though, there were other areas within He embedded process that the Committee believes are worthy of greater attention, and the Committee has additional comments regarding IV&V. IBM's software quality measures show that its internal V&V discovers approximately 80 percent of errors before each new 01 is built and 98 percent of errors before each 01 is first released.
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From page 54... ...
The Committee believes, however, that Me recommendations given below are sufficiently general Hat if they are not already being applied at MSFC, they should be. NASA GUIDELINES AND STANDARDS F'n ding #1: Each software development contractor provides its own development and coding guidelines for Shuttle software.
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From page 55... ...
Herbert Hecht found that: Problems associated with rare conditions emerge as the leading cause of software discrepancies during the late testing stage in this sample. A better methodology for treating rare conditions during design and He earlier test stages could avoid over one-half Of all failures and over two-~irds of He failures in the most severe classifications.5 The IV&V contractor has discovered seven seventy ~ errors on abort scenario definition arid venficadon.
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From page 56... ...
The precision of the Lambert variables was specifically stated in the requirements so ~at, despite the fact that the software was unable to give a crucial response when needed, the development contractors were able to conclude: "Tests show He software had been properly coded by IBM and therefore passed all preflight tests," according to Ted Keller, senior technical staff member at the IBM Shuttle Project Coord~nadon Office, Houston.6 Although the memory in the on-board computers has increased from 104K on the first Shuttle flight to 256K, there seems to have been no consideration given to the idea of eliminating some mixed-precision assignments by changing variables from single to double precision. Had ad He Lambert variables been double precision, convergence would have occurred.
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From page 57... ...
The program relies on the flight software community, which is made up of numerous NASA and contractor organizations, to identify incomplete or misguided requirements before they are passed on to the software development contractors. The program then relies on multiple tests performed by the flight software community and the IV&V contractor to adequately identify problems once the software is delivered.
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From page 58... ...
Instead, because of direction from the program office, in an attempt to save money, the analysis was curtailed. The Committee believes Hat this situation has the potential to gradually reduce the effectiveness of the IV&V, since it places the IV&V contractor in the position of having no higher authority if it finds something it truly believes requires attention.
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From page 59... ...
The previous NRC committee recommended that: Responsibility for approval of hardware certification and software IV&V should be vested In entities separate from ache NSTS Program structure and the centers directly involved In STS development and operation. However, these organizations should continue to conduct activities supporting certification and IV&V.
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