1. NASA. Voyages: Charting the course for sustainable human space exploration www.nasa.gov/pdf/657307main_Exploration%20Report_508_6-4-12.pdf . Accessed 20 Jun 2016.
2. Committee on Strategies for Small-Number-Participant Clinical Research Trials, Board on Health Sciences Policy, Institute of Medicine. Small clinical trials: issues and challenges (compass series). Washington, DC: National Academies Press; 2001.
3. Risin D. Stepaniak PC (eds). Biomedical Results of the Space Shuttle Program. NASA/Sp-2013-607. Washington, DC: US Government Printing Office; 2013.
4. Honda Y, Honda S, Narici M, Szewczyk NJ. Spaceflight and ageing: reflecting on Caenorhabditis elegans in space. Gerontology. 2014;60(2):138–42.
5. Musson D, Keeton KE. Investigating the relationship between personality traits and astronaut career performance: retrospective analysis of personality data collected 1989–1995. December 2011. NASA/TM-2011-21735. http://ston.jsc.nasa.gov/collections/trs/_techrep/TM-2011-217353.pdf . Accessed 20 Jun 2016.