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Appendix F

Re-Entry Risk Formulas

Fernand Alby

The risk from falling debris during an atmospheric re-entry can be expressed in different forms:

• Probability of one casualty P(1)

• Probability of n casualties P(n)

• Probability of at least one casualty P(1)

P(≥1) = P(1)+P(2)+…+P(N)

• Expected value for the number of casualties E

E = 1P(1)+2P(2)+…+NP(N)

where N is the number of inhabitants in the area concerned.

The purpose of this appendix is to provide the formulas for calculating those various values and then to compare their orders of magnitude in a few typical scenarios.

Take a cell on the ground with an area equal to S that contains N inhabitants. Consider the fall of a single piece of debris inside this cell. The casualty area Ac for ...

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