To expedite determination of whether a system struck by natural lightning should be launched or retested, Aerospace created a patented process called the chain algorithm, which employs data from the hybrid on-line lightning monitoring system. Its use reduces the number of damaged space vehicles that are launched and avoids unnecessary retesting on the ground.
Software based on this algorithm can be made generic, to complement any risk-assessment procedure. It can also be compartmentalized, so that its only negotiable area is system-specific information (threshold levels, stress profiles) that can be easily input, in simple formats, and in an appropriate security environment.
Many present lightning retest and damage-search criteria are based on simple, exclusive AND/OR logic. With AND logic, retest and damage search are invoked only when all sensor readings equal or exceed a threshold; with OR logic, any sensor reading that exceeds a threshold invokes retest and damage search. The AND logic leads to insufficient testing, which is purposely avoided because of conservatism. The widely used OR logic leads to excessive retesting, resulting in unnecessary delays and cost and schedule impacts.
The chain algorithm adopts an intermediate approach. It contains logic that specifies the relative importance of all identified modes of coupling lightning to the space system under consideration, and reflects the configuration of all ports of entry for lightning energies being monitored. These prioritizations are accomplished by introducing channel-weighing factors and retest indexes.
The algorithm can be applied separately to sensors monitoring space-vehicle circuits as well as to those monitoring launch-vehicle circuits, giving each contractor information about its own systems, in addition to overall system health. Stress and strength information can be given to identify circuits most likely to be damaged. Most of the algorithm's inputs can be obtained in prelaunch and postlaunch activities, so it requires minimal real-time data processing.