National Aeronautics and Space Administration Authorization Act of 2020 The bill reauthorizes the National Aeronautics and Space Administration (NASA) through FY2020. The bill authorizes NASA programs, activities, reports, and reviews, including those regarding a Moon to Mars Program, low-earth orbit activities, small satellites, commercial Earth observation, the wide field infrared survey telescope, the stratospheric observatory for infrared astronomy, Mars communications infrastructure, a commercial lunar payload services program, a dedicated space-based infrared survey telescope mission, near-Earth objects, a space weather research to operations program, testing facilities for in-space propulsion, space nuclear systems, and orbital debris mitigation. NASA shall arrange for a review of the Human Research program related to long-term human spaceflight, continue operations of the International Space Station (ISS) through at least 2028, transmit an ISS Deorbit Capability and Plan, arrange for the development of a comprehensive set of requirements to support life and physical sciences research in microgravity following the end of ISS operations, develop a Mars sample return strategy and plan, establish a data science and management initiative, arrange for a review of the University Leadership Initiative, and arrange for a review of the National Space Grant College and Fellowship Program. To advance progress toward federal STEM (science, technology, engineering, and mathematics) education goals, NASA shall establish an Office of STEM Engagement. The Government Accountability Office shall, among other things, review NASA's space communications and navigation programs, activities, and plans.