Fuel Capsule Vent System Development for the Viking Radioisotope Thermoelectric Generator

A fuel capsule vent system was developed and designed for the radioisotope thermoelectric generator (RTG) in support of the upcoming Viking mission to Mars. Helium is continuously produced within the fuel capsule as a result of isotopic decay. By venting the helium external to the RTG, the initial RTG fill gas is maintained for maximum thermal efficiency. This reduces degradation of thermoelectric converter performance and provides the maximum electrical power for the mission. The logic and analysis, which led to the selection of a closed helium storage system, were made.