ARAC's radiological support of the Cassini Launch

The Atmospheric Release Advisory Capability (ARAC) program at the Lawrence Livermore National Laboratory (LLNL) was the U.S. Department of Energy atmospheric modeling resource used for the contingency of potential radiological releases during the launch of the Cassini mission. Having the ARAC system up and running was one of the launch criteria during the countdown. The ARAC Center at LLNL forecasted detailed weather conditions and delivered consequence assessments for potential accident scenarios to NASA before and during launch operations. A key aspect of ARAC's support was to acquire a variety of meteorological data for use in both forecast and real-time model calculations. ARAC acquired electronically two types of real-time observed meteorological data: 1) the set of on-site tower and profiler data via the Cape Canaveral Air Station (CCAS) Meteorological Interactive Data Display System (MIDDS), and 2) routine regional airport observations delivered to the ARAC Center from the Air Force Weather Agency. We also used two forecasted data sources: 1) the U.S. Air Force 45th Weather Squadron at CCAS forecasted soundings for launch time, and 2) the Navy Operational Regional Atmospheric Prediction System (NORAPS) prognostic model which ARAC ran over the Cape. The NORAPS runs produced detailed 24-hr forecasts of 3-D wind fields. ARAC used default radiological accident source terms involving the potential destruction of Cassini�s Radioisotope Thermoelectric Generators (RTGs) during 3 phases: 1) before the launch, 2) during the first 5 sec after ignition, and 3) from 5 to 143 sec after ignition. ARAC successfully developed and delivered dose and deposition plots at 24 hours, 3 hours, and 30 minutes before each of the launch windows