NASA announced the creation of this astronaut group in October 2011 and accepted applications for astronaut hires between November 2011 and January 2012.
A near record number of applications - 6,372 - were received. The only year NASA has received more applications was in 1978 leading up to the Space Shuttle program.
The Group 21 Astronaut Candidates (the term for a newly selected NASA astronaut who has not completed basic training and is not yet eligible for mission assignment) arrived at the Johnson Space Center in Houston for training in August 2013. Group 21 astronauts completed training in July 2015 and are available for future missions.
The young class will join 47 other active NASA astronauts. One of the agency's long-term goals is to send a crew on a mission to a near-Earth asteroid by 2020, in preparation for an eventual trip to Mars.