Space.com. Retrieved 30 January 2012. ↑ http://www.nasa.gov/sites/default/files/632697main_NASA_FY13_Budget_Summary-508.pdf ↑ http://www.nasa.gov/pdf/750614main_NASA_FY_2014_Budget_Estimates-508.pdf ↑ 2015 NASA Budget Estimates 1 2 3 2016 NASA Budget Estimates ↑ Clark, Stephen (2014-12-14).