NASA wants to send astronauts to the moon in 2024 with its Artemis program, build an outpost, and use it as a proving ground for Mars.

The first human mission to Mars may cost more than $200 billion, according to a recent US government estimate.

A joint mission with China, which also plans to eventually send people to Mars, might ease the financial burden — but US law restricts NASA from teaming up with the nation.

Jeff DeWit, NASA's chief financial officer, told Business Insider that he wants "to see an American flag" on Mars first, not a Chinese one.

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NASA is pressing to return astronauts to the moon in just five years, then launch the first crew to Mars in the 2030s.

The latter journey may cost the US hundreds of billions of dollars. But an agency executive says the US has no plans to share the hefty cost — and the immortal glory — of such a feat with China, a nation that has similar ambition and resources to put people on the red planet.

"There is still a space race where we want our country to do it first," Jeff DeWit, NASA's chief financial officer, told "Business Insider Today," a top daily news show on Facebook, in July.

Right now, at the direction of President Donald Trump's administration, NASA is focusing on sending people back to the moon for the first time since 1972. The agency's current goal is to land the Artemis mission, as it's known, in 2024.

Read more: Astronauts explain why nobody has visited the moon in more than 45 years — and the reasons are depressing

But as NASA administrator Jim Bridenstine reminded President Trump on the eve of the Apollo 11 lunar landing's 50th anniversary, the agency sees the moon as a "proving ground" for longer, harder crewed missions to Mars.

"When we go to Mars, we're going to have to be there for a long period of time," Bridenstine told Trump on July 19 in the Oval Office. "So we need to learn how to live and work on another world."

That is, assuming NASA and its international partners can scrounge up the cash required to make an interplanetary journey a reality.

'I want to see an American flag' on Mars

An illustration of Russian, American, and Chinese flags on Mars. NASA; Business Insider

A 2014 National Research Council report suggests the first human journey to Mars before 2050 may cost NASA as much as $220 billion. Sending multiple missions to explore the red planet in a sustained, meaningful way could raise the bill to more than $2 trillion, according another estimate.

Cost sharing with other nations has proven an effective way for NASA to achieve its goals in space without footing the entire bill. The International Space Station (ISS): a roughly $150 billion laboratory involving more than 15 nations, is a shining and still-current example. Even Russia, an increasingly adversarial partner, continues to collaborate with the US in orbit.

"They're going to help us with going to the moon," DeWit said of Canada and Japan, two other ISS partners. "We have some great partnerships right now and that cost-sharing has been great."

An illustration of China's planned Mars Global Remote Sensing Orbiter and Small Rover mission, or HX-1. Here a rover is shown leaving a lander to explore the Martian surface. Chinese State Administration of Science/Xinhua Meanwhile, though, the China National Space Administration (CNSA) is landing probes on the far side of the moon, scouting for permanent outpost locations, planning Mars-sample return missions, and more.

Its timeline is not as aggressive as NASA's, but the CNSA appears intent on launching people to Mars as soon as the 2040s.

Read more: 'This is more than just a landing': Why China's mission on the far side of the moon should be a wake-up call for the world

Teaming up with China, then, might make sense for the US from a budgetary perspective. The space agencies of both nations have tried thawing relations in recent years, and with some success. In January, for instance, NASA held discussions with China about collaborating on part of its Chang'e-4 robotic moon landing.

There might be more collaboration, but it requires permission from Congress. That's because, in 2011, US lawmakers voted to greatly restrict NASA-CNSA collaboration over espionage risks.

"There are rules in place of which countries we can't partner with, and China's one of those," DeWit said.

Still, DeWit seemed to have no qualms about the restrictions and NASA aiming for Mars with limited outside help.

"One thing I want to make sure is when we land on Mars, that's an American flag we're planting," DeWit said. "That's important to everybody. It's American taxpayers paying for it. You want an American flag planted. That's a big thing."

'A race to Mars will be a waste of taxpayers' money'

A NASA artist's concept depicts astronauts and human habitats on Mars. NASA

Zong Qiugang, an astrophysicist at Peking University who's previously worked NASA and other space agencies, told the South China Morning Post in 2016 that "a race to Mars will be a waste of taxpayers' money" because it's exceedingly difficult.

"If we are going to Mars, to send the first human visitors there and bring them back, it will go beyond the capability of any single nation," he said.

For NASA's part, getting back to the moon in 2024 is already proving a challenge. Key members of Congress are balking at raising NASA's budget by another $1.6 billion for what Bridenstine and DeWit call a "down payment" to jump-start Artemis — in particular to start building necessary spaceflight hardware.

"What we really need, if we want to hit the target of 2024, is we've got to start securing a lander. We don't have a lander right now," DeWit said. "Part of that's going to be a down payment on getting the lander started — it's going to take time to get that. So the trade-off is going to be, if we don't get the $1.6 billion, it's going to make the target of 2024 harder to hit."

An illustration of SpaceX's Starship vehicle on the surface of the moon, with Earth in the distance. Elon Musk/SpaceX via Twitter NASA is currently grooming private companies for lower-cost help. One is Blue Origin, headed by Jeff Bezos, who debuted a "Blue Moon" lander design for Artemis in May. Another is SpaceX, founded by Elon Musk, which is developing a towering and fully reusable launch system called Starship.

Read more: How SpaceX's new Starship launch system compares to NASA's towering moon rockets

If Musk has his way, though, SpaceX may one-up its competition — and NASA itself — by setting down an uncrewed Starship on the lunar surface in 2021.

"It may literally be easier to just land Starship on the moon than try to convince NASA that we can," Musk told "CBS Sunday Morning" in July adding: "'Hey, look. Here's a picture of landing there right now!' That might be the better way to do it."

DeWit told Business Insider he was skeptical about that ambition, but was also encouraging.

"More power to him. I hope he does it," DeWit said. "If he can do it, we'll partner with them, and we'll get there faster."