Casualty expectation

December 2020: the FAA publishes Part 450 of its rules, which caps a launch's collective casualty expectation at one in ten thousand. Casualty expectation is a probabilistic quantity. For a given launch or re-entry, it aggregates the probability of failure at each instant of flight, the resulting debris dispersion and the density of the population overflown, and produces an average number of serious casualties expected. It serves as a licensing criterion rather than a communications figure. Licensing regimes set a threshold below which a flight may be authorized, on the order of one ten-thousandth of a casualty per launch under American regulation. That calculation drives flight corridors, maritime exclusion zones and launch windows. Its logic is that of an accepted collective risk rather than an individual one, which makes it counter-intuitive to the untrained reader: a figure far below unity denotes an expectation, not a certainty of no harm. For insurance it is the entry point of the third-party liability calculation, since the same modeling is used to estimate the maximum probable loss that sets the amount of cover the license requires.