What type of surface should payload modules always be placed on during handling?

The correct answer is that payload modules should always be placed on a grounded work surface during handling. This is vital for preventing electrostatic discharge (ESD), which can be harmful to sensitive electronic components commonly found in payload modules. Grounded surfaces help dissipate static electricity safely to the ground, minimizing the risk of damage that can occur due to static buildup.

While other surfaces like a wooden table or a padded safety mat may provide physical support, they do not ensure effective grounding. A metallic surface might seem appropriate for grounding purposes, but not all metallic surfaces are properly grounded or safe, which poses a risk. Therefore, a dedicated grounded work surface is explicitly designed to manage static and provide a safe environment for handling sensitive equipment, making it the most suitable choice for this scenario.