Physiological Issues in Human Spaceflight: Review and Proposed Countermeasures This article by Grant Bonin explores some of the physiological problems faced by astronauts during extended periods of space travel. Bonin notes that early stages of exploration under hostile conditions have primarily been dominated by technological concerns, with matters regarding the health and well-being of explores themselves limited to issues of basic survivability. This phenomenon can be traced back to early maritime exploration. Early focus on manned spaceflight followed the pattern. Space exploration over the past half century has focused mainly on the development of propulsion systems capable of lifting humans beyond the boundaries of Earth's gravity. Physiological concerns have generally been dealt with on a per issue basis rather than a preventative basis.

Bonin contends that learning to combat the physiological issues of exploration has been a largely iterative process throughout history. However, an iterative methodology and slow evolution are not realistic in dealing with the physiological issues...

Unlike the environments faced by past explorers, space is both uniquely hostile and uniquely difficult to access. Because of these factors the slow refinement of knowledge in space medicine typically comes at too high a cost, both in terms of capital investment and human lives.
Space physiology is in contrast to most other fields of medical study more constrained due to the realities that of the high cost plus fewer patients creates a more risk- adverse environment. This means less tolerance for the sort of risks and mistakes that have been necessary for the development of medical knowledge historically. This unique combination calls for highly robust biomedical research and development in human spaceflight, especially as longer-term human expeditions beyond near-Earth to destinations such as Mars are considered.

The article notes that human beings have yet to be sent on interplanetary expeditions and even though we have almost 5 decades of manned spaceflight our understanding of the physiological changes experienced by astronauts during long duration…