Tesla and SpaceX founder Elon Musk offered a rare criticism of NASA and the Donald Trump administration Tuesday evening when he said via Twitter that a recent authorization bill would have little effect on furthering NASA’s mission.

"This bill changes almost nothing about what NASA is doing. Existing programs stay in place and there is no added funding for Mars," Musk tweeted.

When pressed for more details about his opinion of the legislation signed earlier that day by President Trump, Musk added, "Perhaps there will be some future bill that makes a difference for Mars, but this is not it.”

Read: President Trump Signs NASA Authorization Act

The bill, S.442, generated headlines upon its signing because the text of the legislation includes mention of a “journey to Mars.” However, as Musk pointed out, it does not actually take steps to make such a journey happen as the bill doesn’t provide any funding for NASA; that will be left for appropriations committees.

Even during the signing of the bill, Trump seemed less than enthused about the possibility of additional space exploration funded by the U.S. government.

Republican Congressman John Culberson of Texas compared the Trump administration’s vision of space to President Dwight Eisenhower’s interstate highway system, stating, “future generations will remember that President Donald Trump was the father of the interplanetary highways system.”

Trump replied to that suggestion by saying, “Well, that sounds exciting,” before insisting, “first we want to fix our highways.”

The statement echoed the President’s insistence that the authorization act wasn’t about expanding U.S. initiatives for space exploration but was instead about jobs. “It's a lot of jobs, and these are great jobs," he said.

Read: Elon Musk Plans Interplanetary Transport System To Get Humans To Mars

For Musk, who holds a personal obsession with the possibility of humans traveling to Mars, the lack of clear support for such initiatives from the country’s space program likely comes as a disappointment.

Musk has been slow to criticize the President, often requesting patience from people in response to Trump’s actions—though he did offer a critique of the President’s travel ban that barred citizens of seven majority-Muslim countries from entering the U.S. The PayPal co-founder remains a member of Trump’s economic advisory board.