[Sea-sa] Current version of "3 Cases" diagrams for the ASL document

[Shames, Peter M (312B)]

Dear SAWG,

Attached is the current version of the “3 Cases” diagrams for the ASL GB.  At this point we will have to stop calling it “3 cases” because we now have six of them, including a new “Case 0” where there are no “MO” services or framework anywhere (the current state).  We have two variants of “Case 3”, one with the MO framework only in the Real Time Computer and one where it is also  in the “MO Device”.    These cases now make it clear that the Spacecraft Computer uses some sort of Real-Time OS and that the software that runs on these Spacecraft must (typically) adhere to Class A/B software processes and testing.  This implies that any MO functionality migrated on-board will have to comply with these stringent, and costly, processes.

The last chart, Case 4, was added at Roger’s request.  As Roger pointed out, the migration of significant MO functionality on-board is likely to incur significant costs, but that may be avoided if a second, non-real-time, computer is put on-board.  For missions that wish to adopt this approach this second, non-real-time, computer may run the MO framework and MO services but avoid the Class A/B development and testing costs.  See https://nodis3.gsfc.nasa.gov/npg_img/N_PR_7150_002B_/N_PR_7150_002B_.pdf for the NASA definitions of Class A/B and their relationship to CMMI guidelines.

If any of you have feedback on these please provide it ASAP.  If you have an alternate reference for Class A/B software please provide it.  I believe that ESA also uses these processes.  And I’ll note that there is a Class A/B/C/D set of categories for medical devices, but they seem to have inverted the order.  Class D for medical devices is the most stringent, for NASA it is Class A.

Thanks, Peter


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