ncludes the identification and removal of errors and restoration of valid subsystem states and, where possible, validation of the completion of successful recovery operation. Techniques and methods which accomplish fault tolerance using hardware techniques with very localized detection, containment, and correction or recovery provisions are termed fault masking; many of the techniques which have been classically used in single event upset mitigation are considered to be in this category. It must be demonstrated that adequate testability is provided to detection and correction/recovery provisions, ensuring that manufacturing or component defects do not exist in systems produced for payload use which compromise the operation or performance of fault tolerance provisions. Furthermore, circuitry added to enable such testability must be examined for the propensity to introduce new fault conditions or to exacerbate the rate of occurrence of on-orbit faults. System integration and validation and verification activities must include the ability to establish that the design supports the qualitative goals and that quantitative requirements established for the fault tolerance provisions are achieved. Methods and provisions must be utilized in subsystem evaluation and for various levels of system integration whereby fault injection capability is utilized to verify the performance of detection and correction/recovery provisions. Qualitative evaluation of fault tolerance design provisions include the use of formal and heuristic methods, test, and experimentation to verify the absence of design faults, to demonstrate consistency with system security provisions, and to demonstrate the operability of detection and recovery provisions. Quantitative evaluation includes the use of fault injection to obtain information about fault coverage, execution time performance of recovery provisions, and the effects which faults present to system operations when detection and recovery provisions are not totally effective. Prediction of availabi