On Tuesday, March 1, 2016, Commander Scott Kelly returned home from the International Space Station after twelve months working off the Earth, for the Earth. His year in space will pay scientific and medical dividends for years to come, helping pave the way for future astronauts to travel to Mars and beyond.

The goal of sending American astronauts to Mars in the 2030s, which President Obama announced at the Kennedy Space Center in Florida in April 2010, is increasingly widely accepted as a “must do”—the logical next destination in the human exploration of space. Achieving that goal will not be possible without the kinds of insights about the physiology of long-duration spaceflight that NASA designed this mission to acquire.

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Dr. John Holdren is the assistant to the President for Science and Technology, Director of the White House Office of Science and Technology Policy, and Co-Chair of the President’s Council of Advisors on Science and Technology. Charles Bolden is the administrator for the National Aeronautics and Space Administration. A veteran astronaut and space shuttle commander, he is a retired major general in the US Marine Corps.

The first human missions to Mars are likely to last about two and a half years. That means prolonged exposure to cosmic radiation and to weightlessness—with its direct physical effects on circulation, fluid distribution in the body, and musculature—as well as metabolic, microbial, and perhaps neurological changes. The willingness of Commander Kelly to sign up for a very closely monitored year in space (on top of his six months total time in orbit from his previous three missions as an astronaut) provided an extraordinary opportunity to increase our understanding of these effects and how to deal with them.

The opportunity was made all the more extraordinary because of the participation of Scott Kelly’s identical twin, Captain Mark Kelly, a former astronaut who has been closely monitored on Earth for the year Scott has been in orbit. This has provided an invaluable benchmark against which to measure the physiological changes that Scott experienced in space. Both twins will continue to be monitored for at least one year after Scott’s return.

Successfully meeting the challenge of sending humans to Mars is also going to require continued progress in three other domains: advanced technologies for life support and habitation, power supply, radiation protection, in-space maintenance and repair, and propulsion; partnership between government and industry; and international cooperation. Under President Obama’s leadership, with help from the Congress, NASA has been moving energetically ahead on all of these fronts.

The ISS plays a key role in all three. It is indispensable as a test bed for the advanced technologies that traveling to Mars and other deep-space destinations will require; as a destination for astronauts and cargo that can support the emergence of a robust commercial space sector; and as a focal point for maintaining and strengthening international cooperation in space exploration. That’s why one of the cornerstones of the “reset” of US space policy President Obama announced in early 2010 was to commit to extending the operating life of the station, initially to at least 2020 and more recently to at least 2024.

Solidifying the future need for transport to the ISS in this way provided the basis for success in turning increasingly to the private-sector to carry not only cargo but also astronauts to the Station.

What a success this has been! When the President said in 2010 that “we will work with a growing array of private companies competing to make getting to space easier and more affordable,” few would have imagined that less than six years later, commercial carriers would have transported 35,000 pounds of space cargo to the ISS and would be poised to carry US astronauts there by late 2017, or that Americans in 2016 would be working at more than 1,000 companies across virtually all 50 states on commercial space initiatives of all kinds.

As the missions that send humans into space and sustain them there become ever more ambitious and complex, the case for countries working together to carry them out becomes ever stronger. The ISS, which is by far the most ambitious and complex such undertaking to date, is a showcase for that principle. The Station is operated by the space agencies of the United States, Canada, Europe, Japan, and Russia, and people from a total of 18 countries have spent time there.

The degree of international partnership in the ISS was of course fully evident in Commander Kelly’s mission: Astronauts and cosmonauts from seven different nations were present on the Station in various combinations during Scott’s stay, and his fellow pioneer over the entire “one year” adventure, from launch from Russia’s Cosmodrome at Baikonur in March 2015 to touchdown a few days ago in the Kazakhstan desert, was Russian cosmonaut Mikhail Kornienko. He, too, was extensively instrumented and monitored to help understand the effects of such extended exposure to the rigors of spaceflight, and full sharing of the data obtained from Scott, Mark, and Mikhail during the mission and over the subsequent year will contribute importantly to the advance of knowledge about space physiology.

When humans finally travel to Mars—in an undertaking even more ambitious and complex than construction and operation of the ISS—it seems only sensible that it will be done in international partnership. Furthermore, when that great joint venture happens, it will succeed only because of the practice in international partnership that the International Space Station has provided.

Scott’s superb photos from his year in space, his imaginative use of social-media posts, and the downlinks in which he shared his experiences for students around the world also showed once again how the great adventure of space exploration can inspire and engage the public, above all the young people from whom the next wave of space explorers will come. It is a little noted but remarkable fact that kids who today are 15 years of age or younger have lived every single day of their lives with astronauts like Scott Kelly and his multinational colleagues living and working together in space. Because of the courage and dedication of the space pioneers of yesterday and today, it may well be that the children and grandchildren of today’s young people will live their entire lives in a time of continuous human presence on Mars.

Commander Kelly, congratulations, thank you, and welcome back!

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Welcome Home, Scott Kelly. Now Let’s Go to Mars