This chapter discusses the generation of the appropriate human-robot ratio for sociotechnical systems where a robot is being used for a novel task. Overall safety is considered as a driver in selecting the human-robot ratio. The human-robot literature has ignored safety, making default assumption that low human-robot ratios are desirable per se, and often pursuing an arbitrary goal of 1:many based on expected advances in vehicle autonomy. Instead, the real goal is the human-robot ratio that maximizes both the safety of team, bystanders, and robots (success of the enterprise) as well as logistical efficiency. The chapter presents a new technique for projecting the safe human-robot ratio: viewpoint-oriented CWA. Viewpoint CWA is an extension of cognitive work analysis (CWA); it concentrates on the perceptual foci of the team members as the key affordance in determining which roles can be safely merged or made autonomous. The technique is illustrated by a review of actual human-robot teaming for urban search and rescue, a remote presence application similar to military operations in urban terrains (MOUT), where tactical users are projecting themselves into the environment via the robot. These teaming experiences include one deployment of a heterogeneous unmanned aerial vehicle-unmanned surface vehicle (UAV-USV) team to Hurricane Wilma, three deployments of UAVs to incidents (Hurricane Katrina, Hurricane Wilma, Berkman Plaza II collapse), and deployments of unmanned ground vehicles (UGVs) to five incidents (World Trade Center, LaConchita mudslides, Midas Gold Mine Nevada, Crandall Canyon Gold Mine, Utah, Berkman Plaza II collapse), plus demonstrations of basic research in UAV-UGV and UAV-USV teaming, and formal studies of mixed teams. Using the findings from applying viewpointoriented CWA, the chapter proposes a formula establishing the baseline safe human-robot ratio, Nh= Nv+Np+1, from which any changes would need to be justified. The chapter concludes with a discussion on how the human-robot ratio might be safely reduced and concerns that must be addressed.
