NASA’s labor pool is overloaded with people soon eligible to retire. A pipeline once filled with American science and engineering graduates is shrinking. Students no longer see the aerospace industry as a choice career path. Higher-paying private sector jobs are alluring, and interest in federal service is declining. Together, those factors raise serious questions about NASA’s ability to recruit and retain a new generation of scientists, engineers and technologists needed to send astronauts back to the moon by 2020 and then on to Mars years after that.