SA Forum is an invited essay from experts on topical issues in science and technology.

This week NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko will launch to the International Space Station (ISS) to begin a yearlong mission onboard the orbital laboratory, where they will conduct research to test how the human body endures a long-duration stay in space. Their mission is part of the work NASA is presently doing on the ISS to develop and test a whole host of long-duration mission capabilities and health-risk mitigations that are moving us forward toward a future Mars mission. Sustained risk reduction research and testing on the ISS provides the most viable and best path to sending astronauts to the Red Planet.

Contrary to the opinion the editors of Scientific American expressed in their commentary, "A Waste of Space," the ISS is the most important laboratory for implementing exploration-enabling research. Furthermore, the NASA risk reduction strategy to protect the health and well-being of astronaut explorers has been vetted by the National Academies. With the launch of the ISS one-year mission, the agency is making an important move to begin extrapolating what we know about ISS six-month missions to the requirements for a journey to Mars and back. The ISS one-year mission fits in our overall risk mitigation strategy in multiple ways.

First, it gives us an initial opportunity to examine in detail the physiological and psychological effects from exposure over a longer mission. Whereas we have a significant evidence base of similar effects during six-month missions for comparison, a yearlong study on the two crew members will expand our ability to plan and execute longer deep-space human voyages with higher probability of success. Because space physiology can be a complicated business, extrapolating ISS one-year human data to a 30-month Mars round-trip will leave us with fewer uncertainties. Furthermore, the unexpected opportunity to compare data from Scott Kelly on the ISS with his identical twin brother on Earth, former astronaut Mark Kelly, will let us explore for the first time how genetic expressions might be altered by long-duration spaceflight. This will provide us with initial insight into the possibility of using emerging personalized precision medicine to address human health exploration risks in a more effective manner.

NASA has extensively studied alternatives to the ISS, such as rotating spacecraft as a potential solution to providing artificial gravity for long-duration space exploration missions. The editors of Scientific American endorse the rotating spacecraft idea Konstantin Tsiolkovsky studied in 1903 before the dawn of the space age. But Tsiolkovsky clearly did not appreciate the complexity of the human vestibular system and the inherent disorientation and confusion that might be created by the cross-coupled angular accelerations experienced by an individual making head movements in a rotating environment. NASA scientists have been well aware of this potential issue for some time. Whether humans can adapt to the vestibular dysfunction is uncertain and this would need to be resolved, along with the added engineering complexities of such a vehicle, before we could even consider committing to a rotating spacecraft for a deep-space mission. Our experience with ISS six-month missions is that current countermeasures can protect most of the physiological systems (bone, muscle and cardiovascular) from deconditioning in space. Exercise countermeasures are also important to psychological well-being and would be part of any long-duration space mission, with or without artificial gravity, just as it is part of a healthy lifestyle here on Earth. The current cost-benefit analyses do not yet approach the levels needed for adopting rotating spacecraft approaches.

The ISS, via its long-duration human mission capability and research, is already producing the keystone knowledge on systems, technologies and operations necessary to maintain crew members' health and guide a future Mars mission along the most efficient, effective and lowest-risk path.

William H. Gerstenmaier is NASA’s associate administrator for Human Exploration and Operations.