NASA administrator Jim Bridenstine announced at a congressional testimony on Tuesday a plan to put human to Mars by 2033 and would request more money to fund the ambitious plan.

It came after NASA's new schedule to land American astronauts on the Moon by 2024, four years ahead of its previous schedule, an aggressive plan U.S. Vice President Mike Pence called a "stated policy of this administration," but American lawmakers worried NASA couldn't meet the deadline.

Pence urged NASA last week to return American astronauts to the Moon within five years, warning that if NASA cannot do it, it is NASA, not the mission, that must change.

Bridenstine cited at the congressional hearing on NASA's budget in fiscal year 2020 the goal of putting astronauts on Mars by 2033 as a reason why NASA need to accelerate the Moon landing plan.

The NASA chief said so in response to U.S. Congresswoman Eddie Bernice Johnson's question why the country need a "crash program for the Moon." "The Moon is the proving ground," said Bridenstine.

"We can move up the Mars landing by moving up the Moon landing."However, NASA's delayed development of its new heavy-lift rocket the Space Launch System (SLS) may mean additional difficulties for realizing these goals on time.

Also, SLS's replacement options or buying commercial rockets like Delta IV heavy rockets and Space X's Falcon Heavy are now technically challenged in terms of thrust capability, launchpad availability and docking ability, according to Bridenstine when addressing a town hall meeting on Monday.

NASA keeps its eyes on human exploration of Mars in 2030s and does not specify any certain year, according to NASA's official website.

Given the distance to Mars, spacecraft has to take at least six months to get there, making the 2033 schedule tighter.

Bridenstine said NASA was preparing a request for additional funding to achieve the 2024 Moon landing goal.

In this year's budget request, NASA planned to devote more than half of its 21 billion U.S. dollars budget to building the key components of the Exploration campaign that will send astronauts to the Moon and beyond. But the request was made with the original Moon landing plan by 2028 in mind.

Bridenstine said NASA would have an updated budget request by April 15.

Xinhua