Administrator Charles Bolden made the announcement Thursday morning, calling the astronauts "pioneers." The four selected are:
All four individuals are experienced astronauts and test pilots. They have a combined total of more than 400 days in space and more than 80 hours of spacewalks.
"These distinguished, veteran astronauts are blazing a new trail, a trail that will one day land them in the history books and Americans on the surface of Mars," said Bolden in a message Thursday to NASA employees.
Boeing and Space X were selected by NASA as the companies which will develop and test the vehicles in which these astronauts will fly. As they do, NASA is freed up to focus simultaneously on developing groundbreaking technology to one day land humans on Mars. "Our commercial crew initiative makes these parallel endeavors possible," Bolden said.
The astronauts will work closely with Boeing, which is designing and building the CST-100 and SpaceX which is building the Crew Dragon spacecraft.
Astronaut Robert Behnken tweeted, "Proud to join this team!"
Gwynne Shotwell, President and COO of SpaceX, issued this statement: "We look forward to working with them even more closely as we prepare for the first human missions to the space station on Crew Dragon. Human spaceflight is why SpaceX was founded, and we look forward to supporting our nation's exploration efforts by launching astronauts from America again."
The first launch of a commercial vehicle is currently scheduled for 2017. The announcement allows astronauts to begin formally training for the mission. Learn more about the astronauts selected. null