During the assembly process team members wore cleanroom suits but also took special precautions to ensure the sterilization integrity of the Lander system. In this image you can see two team members from Martin Marietta lowering the radioisotope thermoelectric generators (RTGs) onto the Lander during assembly. In the case of the RTGs both health and safety and sterilization were critical factors. Sterilization was the single most important requirement of the mission, as one of the key science objectives was to determine if there were forms of life present and active on Mars. Mars surface contamination by earth organisms (bioburden), RTG containment, and sample contamination by Lander descent engine fuel were problems that were critically evaluated and mitigated through extensive analysis and engineering designs. The RTGs seen in this image contained radioactive plutonium, which generates heat that can be converted to electricity, but also emits radiation which, although small, could cause negative health impacts. However the positive attributes including thermal energy which provided power and heat to keep the internal systems warm and functional, and relatively easy containment, made this the optimal choice for power on the Viking Landers. This kind of evaluation and tradeoff was a hallmark of the Viking mission, which was the first mission of its kind, operating with high risk factors including many environmental unknowns, and using relatively new technologies, while innovating others specifically to meet the science and engineering requirements of the mission. The Sterilization requirement for Viking required all landed craft and instruments to be sterilized using a set of criteria defined by the team including baking the entire Lander and subsystems at 111.7 ˚C (233.1 ˚F) for 30.23 h, and using the clean room procedures to handle sterilized elements.