In 2001 Hernandez joined the Johnson Space Center, in Houston, Texas.
Materials and Processes (M&P) branch chief within the Structural Engineering Division. Duties included managing the careers of 30 professional civil servants with diverse set of skills in materials science. Also serve as the overall technical monitor of contractor support that included more than 20 contractors. Responsible for the oversight of the branch's activities in the areas of materials and processes, fracture control, non destructive evaluation, failure analysis, and nano materials research.
Selected by NASA in May 2004. In February 2006 he completed Astronaut Candidate Training that included scientific and technical briefings, intensive instruction in Shuttle and International Space Station systems, physiological training, T-38 flight training, and water and wilderness survival training. On completing this initial training, Hernandez was assigned to the Shuttle Branch to support Kennedy Space Center Operations in support of Shuttle launch and landing preparations. He will work various technical assignments until assigned to a spaceflight as a mission specialist.