8.56 ~2% of range. A typical off-the-shelf unit (such as the National Semiconductor LX3702D differential pressure transducer produced in June 1974) would be accurate to about 2070 N/m 2 (0.3 psi), or 5% of hull pressure. Resolution is theoretically continuous, and in practice depends upon the electronic signal processing accuracy, but a detectable pressure change of 5% is assumed here. For a worst case of the largest compartment with no shielding installed, this corresponds to a loss of 59.9 kg--5% of the compartment's air mass, or 0.0016 % of the total colony atmosphere. The above numbers are for existing units. Cutom made transducers with ranges exactly matched to the prototype pressure should be accurate to 2% of hull pressure. Detecting leaks requires detecting changes in the pressure rather than the absolute pressure level. Better electronic signal processing to fully exploit the continuous resolution could reliably detect pressure changes of 0.1%, equivalent to a loss of 1.20 kg of atmosphere. The sensitivity of such a system might actually be too high: the output would be dominated by minor fluctuations caused by normal operations in the colony. Even better sensitivities are achievable with more sophisiticated units, but the simplicity and reliability of the self-contained semiconductor pressure transducers makes the most practical choice. They are available with temperature compensation, built-in signal conversion for compatibility with standard data acquisition systems for completely automatic monitoring, and have low power requirements. They can withstand a complete loss of pressure on the compartment side. Five hundred and ten are required, one for each compartment. VIII.8.7: Repair: Once a failed or leaking plate has been detected, it must be repaired as quickly as possible to avoid a dangerous accumulation of adjacent failed structural members. A loss of four plates in the outer hull is the worst case damage scenario, so a corresponding repair scenario is considered here. Not every possible damage can be exactly predicted in advance: if it were, the damage could then be prevented, or at least its effects greatly minimized. (The four-plate failure is simply a convenient working assumption.) No piece of repair equipment can be
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