JHU/APL Breakup Analysis Tool (APLbat) for the New Horizons Radiological Contingency

The New Horizons spacecraft will be the first to study Pluto and its largest moon Charon. It launched on 19 January 2006 and will encounter Pluto in 2015. The long duration of the flight, the great distance from the Sun, and the low temperatures in the Pluto‐Kuiper Belt necessitate the use of a Radioisotope Thermoelectric Generator (RTG) for heating and electricity. RTGs provide heat and electricity through the radioactive decay of plutonium dioxide (PuO₂) fuel pellets. The pellets are contained in protective shells called the General Purpose Heat Source (GPHS) modules. As the New Horizons Pluto‐Kuiper Belt mission‐implementing organization. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) was responsible for determining the Earth impact footprint of the GPHS modules in the event of an orbital or suborbital re‐entry accident during launch. The JHU/APL‐developed computer program, APL Breakup Analysis Tool (APLbat), takes estimates of uncertainty in the initial vehicle (spacecraft) position and motion and, using a design‐of‐experiments approach and a six‐degree‐of‐freedom dynamics model, simulates the continued motion of the vehicle, predicts its breakup as it re‐enters the atmosphere, and produces a most probable elliptical Earth impact footprint for the GPHS modules.