Castro worked at NASA for 37 years, from 1977 to 2015. In 1977, she began as a data analyst of the team that planned and executed the Goddard Space Flight Center (GSFC) Spacelab Data Processing Facility (SLDPF). The SPDF is a core space shuttle mission that aims to investigate microgravity, solar physics, crystal growth, and other scientific inquiries. In 1990, she became the first female Mission Operations Manager of the Earth Observing System (EOS) project. It was a vital constituent of the Earth Science Enterprise program of NASA. She supervised the developmental stage of the three EOS missions: terra, aqua, and aura. Castro developed the operations concept of EOS, containing the EOS memoranda, among others. It became the basis of all EOS missions. Half of her 12 years service to NASA, she served a dual role as she also became the Earth Science Constellation Manager.