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Long-Term Challenges to Human Space Exploration


“Mankind is drawn to the heavens for the same reason we were once drawn into unknown lands and across the open sea. We choose to explore space because doing so improves our lives, and lifts our national spirit.”
–  President George W. Bush, January 14, 2004

Artist's impression within AU Microscopii's Disk.

America is heading back to space. 

On December 11, 2017, in the Roosevelt Room of the White House, representatives of the commercial space sector, NASA officials, Apollo 17 astronaut Harrison “Jack” Schmitt and other astronauts, and members of the administration witnessed President Donald J. Trump signing the Space Policy Directive 1, a directive intended to return American astronauts to the moon and to initiate long-term human space exploration.

This signing ceremony took place exactly 45 years after astronaut Jack Schmitt and Apollo 17 commander Gene Cernan left the last human footprint on the moon in 1972.

We have learned that humans can survive living on the ISS station in low Earth orbit (LEO), or spend time exploring the moon, but to colonize the moon or other worlds presents unique challenges. 

Earth has all the ingredients to protect and sustain life. Exploration missions that leave the Earth’s protective sphere, however, will have to overcome many challenges, from conditions in space such as cosmic radiation and hazardous environments to human-specific conditions such as space adaptation syndrome (motion sickness), spatial memory, visual motor performance, bone loss, and the physiological and psychological impacts of living in cramped quarters in zero or low gravity.

Space exploration is more than seeing what is beyond the horizon—exploration also helps us to understand more about our planet, our solar system, our universe, and ourselves. At the very core of human space exploration is the desire to explore the unknown and extend human presence deeper into the solar system. 

As our forebears braved the unknown, sailing the seas to discover new worlds, space pioneers will sail the cosmos to find other worlds in our universe, seeking to blaze the trail for the next generation and beyond.

NASA is charting the course for long-term human space exploration. This webpage covers resources on the challenges of long-term human space exploration as we venture deeper into space to find other worlds.  All items are available at the Headquarters Library, except as noted. NASA Headquarters employees and contractors: Call x0168 or email ( for information on borrowing or in-library use of any of these items. Members of the public: Contact your local library ( for the availability of these items. NASA Headquarters employees can request additional materials or research on this topic.

The Library welcomes your comments or suggestions about this webpage.


The following standards, policies, and procedural requirements can be accessed by anyone through the NASA Online Directives Information Systems or through the NASA Standards website


Institute of Medicine of the National Academies.  Health Standards for Long Duration and Exploration Spaceflight Ethic Principles, Responsibilities, and Decision Framework. Washington, D.C.: The National Academies Press, 2014. ISBN: 978-0-309-29657-1.  
RC 1151 .S64 .I5 2014  BOOKSTACKS
Available Free to All


Longnecker, David E.  A Risk Reduction Strategy for Human Space Exploration of Space, A Review of NASA’s Bioastronautics Roadmap (2006).  Washington, D.C.: National Academies Press, 2006.  ISBN: 978-0-309-09948-6.
RC 1135 .R57 2006  BOOKSTACKS
Available Free to All

National Research Council (U.S.). Committee on the Evaluation of Radiation Shielding for Space Exploration.  Managing Space Radiation Risk in the New Era of Space Exploration.  Washington, D.C.: National Academies Press, 2008.  ISBN: 978-0-309-11383-0.
QB 461 .N375 2008  BOOKSTACKS
Available Free to All

National Research Council (U.S.). Committee for Evaluation of Space Radiation Cancer Risk Model.  Technical Evaluation of the NASA Model for Cancer Risk to Astronauts Due to Space Radiation.  Washington, D.C.: National Academies Press, 2012.  ISBN:  978-0-309-25305-5.
RC 1151 .R33 N385 2012  BOOKSTACKS
Available Free to All

Nicogossian, Arnauld E., Williams, Richard S., et al.  Space Physiology and Medicine: From Evidence to Practice, 4th ed.  New York, NY: Springer Science & Business Media, 2016.  ISBN: 978-1-493-96650-9.
RC 1150 .S63 2016  BOOKSTACKS

National Aeronautics and Space Administration and Vakoch, Douglas A. (Edited by).  Psychology of Space Exploration, Contemporary Research in Historical Perspective.  Washington, D.C.: National Aeronautics and Space Administration, 2011.  ISBN: 978-0-160-88558-3. 
Available Free to All 


Boddy, Jessica. (2006). From shrinking spines to space fungus: The top five dangers of space travel.  Science. Retrieved from,
DOI: 10.1126/science.aal0451

Lloro, V., Giovannoni, L.M., Lozano-de Luaces, Lloro, I. and Manzanares, M.C. (2020). Is oral health affected in long period space missions only by micogravity? A systematic review. Acta Astronautica, 167, pp. 343-350. Retrieved from:

Romero, Elkin., Francisco, David. (2020). The NASA human system risk mitigation process for space exploration. Acta Astronautica, 175, pp. 606-615. Retrieved from:

Angeloni Debora., Demontis, Gian Carol. Endocrine adaptations across physical and psychological stressors in long-term space flights. (2020). Endocrine and Metabolic Research, 11, pp. 21-26. Retrieved from:

Lewis, Cathleen. (2017). Studying Long-Duration Human Spaceflight. Smithsonian National Air and Space Museum Space History, 

Parks, Jake. (2018). How does space change the human body? Astronomy. Retrieved from:


NASA’s Human Research Program

NEEMO – NASA Extreme Environment Mission Operations Project

Explore Moon to MARS


What happens to an astronaut’s body in space

NASA 360, The Future of Human Space Exploration

What is One of the Greatest Challenges for an Astronaut on the Journey to Mars?

NEEMO Video Gallery

NASA Analogs Missions

What are the Next Generation Spacesuits?


Antonsen, Erik. L. (2019). Human System Risk in Spaceflight. Retrieved from NTRS (, 20190032988. 

Easter, Benjamin. (2019). Medical Risks and Capabilities for Human Exploration Spaceflight. Retrieved from NTRS (, 20190025249.


Smithsonian National Air and Space Museum