Accurately assessing the risk associated with the launch of radioactively powered space vehicles
is critical to the success of future space missions.
For missions that travel to distant locations in space, or for vehicles performing on the surface of space bodies, power is presently provided through radioactive sources. Launching these power sources into space requires approval in accordance with Presidential directives and policies; these policies require analysis of the environmental and human health impacts should an accident occur. Radiation dose and cancer risk to the public are driving factors for which generic activity to dose or cancer risk values have historically been used. The Launch Safety program at Sandia National Laboratories has, for the first time, replaced the use of generic values with specific age, particle-size, and radionuclide values. Advanced research has determined the particle sizes generated by a launch accident and this data was used to calculate specific dose and cancer risk values, which were then coupled to geospatial population information to calculate human health impacts at the potential accident locations. This combination has provided a more accurate and realistic prediction capability and has eliminated unnecessary conservatisms that could threaten launch approval and mission success.
Combining the results from advanced modeling capabilities with improved population database
information has provided more accurate prediction of accident scenario effects.
Advances in launch accident modeling enable calculation of the specific particle sizes that would be generated by an accident. Enhanced population databases provide the age breakdown of the population at a given simulated accident latitude/longitude. Coupling these to the models behind the Federal Guidance Report 12/13 dose and cancer risk coefficients provided particle size, radionuclide-specific, population-specific coefficients for the calculation of more realistic population dose and cancer risk. At the same time, the costs and risks associated with more conservative estimates were reduced. This is particularly useful for radioisotope thermal generators (RTGs) that utilize alpha particle emitting materials.
Greatly improved accident impact prediction capabilities have been achieved thereby decreasing
risk and saving time and costs associated with delayed or denied launch approvals.
The use of these coefficients was essential to showing that prior usage of generic values produced estimates of cancer risk that were 2 to 5 time too high for an RTG powered by plutonium-238. This difference was critical in showing that the potential impact of an accident for the Mars 2020 mission corresponded to the Tier II limits of the Presidential Directive, NSPM-20, thus saving the mission time and risk that might have delayed or denied launch approval.