28 July 2005
NASA's New Horizons Mission Final Environmental Impact Statement


What is the launch date and mission? (page v-vi)

Expected launch for New Horizons mission to explore Pluto and its moon is January-February 2006 on board an Atlas V 551 expendable launch vehicle from Cape Canaveral Air Force Station.


How much plutonium is on the mission? (Pages v,  2-9 and 2-10)

One radioisotope thermoelectric generator (RTG) containing plutonium dioxide (PuO2) would be used. (Page v)


The RTG consists of a stacked column of 18 aeroshell modules.  Each module contains about 0.6 kg (1.3 lb) of PuO2.  The total for the RTG is 10.9 kg (24.0 lb) of PuO2 with activity of about 132,500 curies.  The principal plutonium isotope is Pu-238, with a half-life of 87.7 years.  In addition there are smaller amounts of other plutonium isotopes, including a significant amount (12% of total weight) of Pu-239 with a half-life of 24,131 years.  There are even trace amounts of Pu-242 with a half-life of 375,800 years!


Accident Probabilities  (See Pages 2-27, 2-28, 2-29 and 2-30)

(Phase 0 & Phase 1) Pre-Launch and Early Launch: A launch-related accident could result in ground impact in the launch area with release of PuO2 from the RTG.   Total probability of accident (resulting in release) is 1 in 620.


(Phase 2) Late Launch:  A launch accident would lead to impact of debris in the Atlantic Ocean.  No release would occur because undamaged aeroshell modules would survive water impact.


(Phase 3) Pre-Orbit:  An accident during this period prior to reaching Earth parking orbit could lead to sub-orbital reentry.  Breakup of the spacecraft during reentry could result in aerial release over the Atlantic Ocean and southern Africa.  The modules could impact rocks and release PuO2 at ground level.  Probability of accident is 1 in 1,300.


(Phase 4)  Orbit: An accident after attaining parking orbit could result in orbital decay reentries from minutes to years after the accident, affecting Earth surfaces between 28 degrees North Latitude and 28 degrees South Latitude.  More chance for modules to impact with rocks within these latitude bands, releasing at ground level.  Probability of accident is 1 in 1,100.


(Phase 5) Escape: A launch accident which leads to escaping Earth would not release PuO2.


Total probability of an accident resulting in a release across the entire mission is about 1 in 300.


Global Network