President Donald Trump's nominee to lead NASA, Jared Isaacman, leaves his confirmation hearing before a Senate committee in Washington on Wednesday. Isaacman has led two private astronaut flights to orbit. Tierney Cross -NYT

By KENNETH CHANG | THE NEW YORK TIMES

NASA will prioritize sending American astronauts to Mars, President Donald Trump's nominee to lead the space agency told a Senate committee Wednesday.

That led to prickly exchanges between the nominee - Jared Isaacman, CEO of the payment processing company Shift4 Payments, who is a close associate of Elon Musk, the founder of SpaceX- and both Republican and Democratic members of the Senate Committee on Commerce, Science and Transportation. They wondered about the future of the International Space Station as well as Artemis, NASA's current effort to send astronauts back to the moon.

"I don't think we need to make any tough trade here," Isaacman said. "I think we can be paralleling these efforts and doing the near impossible."

Isaacman shared the hearing Wednesday with Olivia Trusty, a nominee to be a member of the Federal Communications Commission. During his testimony, Isaacman avoided direct answers to a number of questions while repeatedly saying that the space agency could work to send astronauts to both the moon and Mars within its current $25 billion budget.

"NASA was built to do the near impossible," Isaacman said.

Sen. Ted Cruz, R-Texas, who chairs the committee, gave Isaacman a lecture about the bipartisan law that dictates NASA's priorities, reading back the portion that states that Mars would be the destination after the moon. The Johnson Space Center is in Cruz's state.

"When legislation uses the word shall, it denotes a mandatory obligation," Cruz told Isaacman. Isaacman said, finally, that he would follow the law.

In response to a question from Sen. Jerry Moran, R-Kan., Isaacman agreed that the massive Space Launch System rocket that has been under development for more than a decade would be the fastest way to get American astronauts back to the moon. NASA currently plans to use that vehicle, which made its debut launch in November 2022, for its moon missions.

The first of those missions, Artemis II, is scheduled for next year and would take four astronauts around the moon without landing. Those astronauts, three from NASA and one from Canada, attended Wednesday's hearing. The next mission, Artemis III, which would land two astronauts near the moon's south pole, is to occur no earlier than 2027.

As someone who has led two private astronaut flights to orbit, lsaacman would, if confirmed, bring to NASA and its $25 billion budget a perspective more in line with newer entrepreneurial aerospace companies like SpaceX.

Sen. Edward Markey, D-Mass., noted the close ties between lsaacman and his companies and Musk. He asked several times whether Musk had been present at Mar-a-Lago in Florida when Trump offered Isaacman the NASA position.

lsaacman did not directly reply, and would only say, repeatedly, that his interview was with Trump. lsaacman also said that he had not been in contact with Musk since being nominated.