Due to safety and security constraints much of the laboratory and systems testing was performed using electrically powered SNAP-19s called ETGs. These units incorporated capsules containing electrical heaters to simulate the thermal power of the fuel capsules. The laboratory images shown here use ETGs.
In this image the ETG is connected to the test interface via cables to record variables such as temperature, power output, and data on the cooling loop (how much flow rate it took to keep the system cool. Simulated tests were done first with the ETGs to ensure they would work during the period the RTGs were encapsulated until the lines were cut just before launch. The testing needed to simulate the temperature ranges (1080 degrees F on the hot side and 330 F on the cold) to comprehend the environment inside the RTGs and outside. By changing the variables and isolating the causes and controlling them, the team was able to create a parametric that mission planners could use to predict the power from the RTGs under different conditions. This would help them understand how power would be affected if the wind was blowing hard, of if it was sunny, and a variety of other factors, and be able to predict power. It also permitted them to predict power as a function of time.