When Neil Armstrong stepped onto the moon in 1969, the United States was widely proclaimed the victor in the space race with the Soviet Union. Today, however, with the U.S. space shuttle program no longer in operation, NASA pays Russia to transport U.S. crews to the International Space Station and the Pentagon depends on Russian rocket engines to launch its military satellites into orbit. In addition, China's space program is growing rapidly, and U.S. officials worry it threatens American space assets, including military satellites. Policymakers also fear that U.S. satellites are at risk from accidental collisions. Meanwhile, NASA is planning for deep-space missions, even as some experts say these missions cost too much and the agency should rely more on private spaceflight companies. Other debates focus on whether the United States should return astronauts to the moon, as President Trump wants NASA to do in the next two years, and whether humans or robots should take the lead in exploring space.