Although humans offer specific advantages in the exploration of planetary surfaces, they have their limitations as well. Because of the harsh environments of the Moon and Mars and the amount of challenging physical work involved, safety considerations will always constrain the amount of time available for people to explore and perform scientific tasks. Humans working in spacesuits will always have less mobility and flexibility than humans working on Earth, despite anticipated improvements in spacesuits. In addition, scientific activities are not the only things people will be doing during human exploration missions. Lastly, as was demonstrated in the Chernobyl nuclear accident, the potential for rapid human reaction in response to a local stimulus or observation has a concomitant potential for rapidly introducing errors.
Robots likewise have limitations.
The creation of nearly autonomous machines with humanlike cognitive abilities continues to elude the robotic research community and may well do so for a considerable time into the future. Given current capabilities, robots require considerable human control and interaction to accomplish most scientific tasks. Their capabilities are appropriate for simple reconnaissance or prescribed activities in which no major difficulties are encountered. Whether their capabilities will remain at this level will depend on advances in robotic technology prior to the initiation of a program of human exploration. Lastly, even though robots are inherently expendable relative to humans, their cost can be sufficiently large that they ought not be exposed to excessive risk.