President Donald Trump has signed a directive to begin the process to return Americans to the moon. The directive, titled “Space Policy Directive 1”, creates a foundation for a future mission to the moon. The directive also establishes a foundation for an eventual mission to Mars and beyond.

The directive would have NASA put people on the moon for the first time in 45 years. NASA sent 12 men to the lunar surface in the late 60s and early 70s. Acting NASA Administrator Robert Lightfoot said in a statement, “NASA looks forward to supporting the president’s directive strategically aligning our work to return humans to the moon, travel to Mars and opening the deeper solar system beyond.” The directive calls for NASA to work with “private sector partners” on the initiative.

Former lunar astronauts Buzz Aldrin and Harrison Schmitt and current astronaut Peggy Whitson attended Trump’s signing ceremony for the directive at the White House in Washington D.C. Taking a prominent place at the signing ceremony was a moon rock collected by Schmitt’s Apollo 17 mission in 1972 that has been dated to be 3.8 billion years old.

President Trump wants the United States to remain the leader in space exploration. Trump said the move was a giant step toward “reclaiming America’s proud destiny in space.” Since Schmitt’s trip in 1972, only the Chinese have visited the lunar surface, via rover. In 2010, then-President Barack Obama said he wanted NASA to be orbiting Mars by the 2030s.

Where the agency will get the cash for the new initiative remains an open question. Currently, U.S. spending on space exploration as a percentage of total federal dollars is close to an all-time low. The agency currently gets roughly $18 billion federal dollars every year, accounting for less than half of one percent of all federal money. The Trump Administration’s proposed budget reduces that total by roughly $200 million.

In 1966, three years before NASA first landed on the moon, the federal government spent about 4.5 percent of the national budget on the agency and its initiatives. Adjusted for inflation, today that number would be about $45 billion. How much the moon landing will cost will be worked out in discussions about next year’s budget for the agency, which must be approved by Congress. According to NASA, initial funding for the new policy would be included in its budget request for fiscal year 2019.