ESTIMATION OF ON-GROUND RISK DUE TO UNCONTROLLED RE-ENTRIES FROM ECCENTRIC ORBITS

Estimation of casualty expectancy associated with a reentry event is important for long-term risk assessment. There are various methods described in open literature to estimate casualty expectancy. These methods assume that reentry take place from circular orbits. But the decay process, from highly elliptic orbits like GTO or Molniya, re-entry is governed by either predominantly luni-solar gravity effect, with drag playing a very marginal role or by a combination of atmospheric drag and luni-solar perturbations. Often, full circularization of orbit prior to re-entry remains incomplete. This kind of scenario also arises when an intermediate stage of a launch vehicle is deliberately left in a low perigee eccentric orbit as a part of overall mission. Here a method is presented for the estimation of casualty expectancy in the event of an uncontrolled reentry from eccentric orbits. Probabilistic estimates of true anomalies of impact points for eccentric orbits are obtained through Monte-Carlo simulations. This proposed method provides confidence intervals on the values of casualty expectancy at different inclinations, besides its average values. Thus it allows mission planner to get a more comprehensive picture on casualty expectancy at different orbital inclinations.