Michael Gazarik, NASA Associate Administrator for Space Technology gives a short presentation on NASA's human exploration path to Mars during a panel discussion moderated by PBS NewsHour's Miles O'Brien at the Humans to Mars Summit on April 22, 2014 at George Washington University in Washington, DC. Photo Credit: (NASA/Joel Kowsky)

William Gerstenmaier, NASA Associatate Administrator for Human Exploration and Operations, right, answers a question during a panel discussion moderated by PBS NewsHour's Miles O'Brien at the Humans to Mars Summit on April 22, 2014 at George Washington University in Washington, DC. Photo Credit: (NASA/Joel Kowsky)

NASA Administrator Charles Bolden delivers the opening keynote address at the Humans to Mars Summit on April 22, 2014 at George Washington University in Washington, DC. Administrator Bolden spoke of NASA's path to the human exploration of Mars during his remarks. Photo Credit: (NASA/Joel Kowsky)

NASA Administrator Charles Bolden answers questions from the audience after giving the opening keynote address at the Humans to Mars Summit on April 22, 2014 at George Washington University in Washington, DC. Administrator Bolden spoke of NASA's path to the human exploration of Mars during his remarks. Photo Credit: (NASA/Joel Kowsky)

NASA Administrator Charles Bolden answers questions from the audience after giving the opening keynote address at the Humans to Mars Summit on April 22, 2014 at George Washington University in Washington, DC. Administrator Bolden spoke of NASA's path to the human exploration of Mars during his remarks. Photo Credit: (NASA/Joel Kowsky)

NASA Administrator Charles Bolden delivers the opening keynote address at the Humans to Mars Summit on April 22, 2014 at George Washington University in Washington, DC. Administrator Bolden spoke of NASA's path to the human exploration of Mars during his remarks. Photo Credit: (NASA/Joel Kowsky)

Miles O'Brien, science correspondant for PBS NewsHour, left, leads a panel discussion on Mars exploration with William Gerstenmaier, NASA Associatate Administrator for Human Explorations and Operations, center, and Michael Gazarik, NASA Associate Administrator for Space Technology, left, at the Humans to Mars Summit on April 22, 2014 at George Washington University in Washington, DC. Photo Credit: (NASA/Joel Kowsky)