Image Description -  0707

This figure depicts a block diagram captioned "Figure 1. Process Flow Diagram 
for Fault Tolerant Design".  The first block in the diagram represents Phase 1, which 
identifies the tolerance of the design.  In this block analytical designs which aid in 
identifying the tolerance of the design are outlined.  These analyses are part variations,
 worst-case circuit, part stress analysis, parts engineering, redundancy, electromagnetic 
compatibility, mechanical integrity and thermal control. 

Block in Phase 1 arrows into a second block below it.  The second is labeled "Phase 2", 
which identifies the mode of the minor failures.  The block suggests that the method by 
which the mode of the minor failures are identified is through failure modes, effects and 
criticality analyses or FMECA, and fault tree analyses or FTA, performed at assembly, 
subsystem, system and interface levels. 

Block in Phase 2 arrows into a third block below it.  The third block is labeled "Phase 3", 
which identifies design features to improve the tolerance of the design to accommodate 
minor failures identified in Phase two.  The listed features include software protection 
algorithms, active redundancy, standby redundancy, ground command, error detection 
and correction schemes.   

Block in Phase three arrows into a decision diamond with word "Risk" written inside.  The 
two outcomes of this decision block are labeled as "Unacceptable" and "Acceptable".  
If the risk decision is acceptable, the diamond arrows into a block labeled as "Test 
Verification".  The suggested test verification methods in this block include Mechanical, 
vacuum, thermal and life testing.  This block arrows into another decision diamond with 
letters F over P written inside.  The two outcomes of this decision block are labeled as 
"Fail" and "Pass".  If the decision at this point is pass, the process ends.  If the decision 
at this point is fail, the process flows back into a block labeled "Phase four" which calls for 
improving the design tolerance and returning back to phase one.

Returning to the decision block labeled "Risk", if the risk decision is unacceptable, again 
the process flows back to block labeled "Phase four" which calls for improved design 
tolerance which requires returning to Phase one and starting the process all over.