The United States wants to send robotic explorers to the moon as soon as next year as a step toward sending astronauts there for the first time since 1972, a NASA official said Monday.

NASA is planning lunar missions beginning next year aimed at developing the capacity for humans to return to the moon, said Cheryl Warner, a spokeswoman for the agency.

NASA will work with private companies, which have not yet been chosen, on the missions, Warner said in a phone interview.

President Trump in December signed a directive that he said would enable astronauts to return to the moon and eventually lead a mission to Mars. Last month he ordered the government to review rules on commercial space flights.

Americans first landed on the moon in 1969, reaching a goal set by President John F. Kennedy in 1961 and capping a decade-long space race with Russia.

Since then, U.S. efforts to explore beyond the Earth’s orbit have mostly focused on remote unmanned spacecraft.