LATCHUP SUPPRESSION TO FACILITATE FAULT-TOLERANCE IN TERMINAL GUIDANCE COMPUTERS

Fault tolerance in a real-time computing environment is a critical need for the terminal guidance computer in interceptors in Ground-based Midcourse Defense (GMD). In much of the GMD system, fault detection, correction and/or compensation can be done entirely in software. But in the case of faults introduced into the guidance computer by radiation, a combined hardware and software approach can be very useful. Specifically, high dose rates can cause logic upset, but can also cause latchup in integrated circuits. The former can be handled by EDAC, or in extreme cases, by a rollback to data stored in non-volatile memory, and re-starting from this earlier point. But if latchup occurs, power to the computer must be toggled off, then restored. This can take much longer that EDAC or rollback. In the short mission duration of an interceptor, this time may not be available. If latchup-immune chips can be employed, coping with high dose rates is greatly simplified, since power doesn't need to be dumped. The proposed program applies to the high dose rate threat a technique developed for suppressing latchup caused by heavy ions in space. Success in this effort will significantly simplify the job of developing a fault tolerant real-time computing environment for GMD.