Commercial Crew is competitive, with contracts up for grabs for Boeing and SpaceX and their capsules Starliner and Crew Dragon , respectively. Right now the two companies each have two test flights remaining before beginning commercial operations, as well abort tests. NASA said SpaceX plans to launch its Demo-1 test flight, which will not have crew, on March 2, while Boeing does not expect to conduct its unmanned flight test before April at the earliest. The second test flights will be the first with humans on board the capsules.

The most pressing topic was NASA's Commercial Crew program, which is in its final stages of testing. Commercial Crew is the agency's solution to once again launching U.S. astronauts from U.S. soil. Since the end of the Space Shuttle program in 2011, astronauts have flown aboard Russian Soyuz — at a cost to NASA of more than $70 million per seat.

NASA is focused on using partnerships with companies like SpaceX and Boeing , rather than contracting and operating the rockets and spacecraft itself. NASA Administrator Jim Bridenstine spoke with CNBC's Jane Wells about the key programs to the future of U.S. space exploration while at the 52nd World Ago Expo in Tulare, California, on Tuesday.

The U.S. government is relying more than ever on private companies to explore and develop technology in space, whether its reaching the International Space Station, returning to the surface of the moon or getting humans to Mars for the first time.

Similarly staggered in timing, SpaceX says its Demo-2 crewed flight will be in July, while Boeing is aiming for no earlier than August. However, Bridenstine says that this does not mean it is certain SpaceX will launch humans before Boeing.

"I think there is going to be less time between the uncrewed vehicle for Boeing and the crewed vehicle for Boeing, and longer time between SpaceX [capsule test flights] – which means, whoever gets to fly that first crew, we don't know right now," Bridenstine said.

A spokesman for Boeing said, "Both Starliner capsules that will fly this year are crew ready. During the uncrewed flight we will evaluate all test objectives except those that require a person in the capsule. Our flight with a crew depends on a successful uncrewed flight."

Because Boeing is reusing its crew modules, the company expects the capsules will be essentially the same between the first test flight and the second. While the schedule has been delayed multiple times over the last several years, Bridenstine said he is "highly confident" that the U.S. will be launching "American astronauts from American soil on American-made rockets" by the end of 2019.

Shifting to NASA's next human spaceflight ambition, Bridenstine addressed President Donald Trump's declaration that the U.S. must return Americans to the surface of the moon and onward to Mars. NASA is announcing more of its plans for returning humans to the moon at a conference on Thursday, focusing on the spacecraft that will land on the surface. Bridenstine said NASA's lunar plans are also "likely to be a public-private partnership" and explained more of his idea of who those customers will be.

"When I say many customers I mean there will be sovereign nations that have their own astronaut programs, and there is going to be space tourists as well, but we are going to be one customer of many customers in a robust commercial marketplace. Well what we are going to do now is we are going to take that model ... and we are going to apply that to everything between the Earth and the moon so that we have a sustainable return to the moon."

Bridenstine also set his expectation for NASA's return, saying "the goal is to have the first human lander on the surface of the moon in 2024."

Why return to the moon? One reason is for the resources on its surface, which include "water ice" and rare Earth metals. Bridenstine gave his case for the value those resources represent, which could be worth "tens of trillions of dollars," he said.

"In 2009, NASA made a discovery, there are hundreds of billions of tons of water ice on the surface of the moon. What does that mean? That means you've got air to breathe: Oxygen. You've got water to drink: H2O. But you've also got rocket fuel on the surface of the moon. Hydrogen and oxygen, cracked into its component parts, put into cryogenic form, it's the same rocket fuel that powered the space shuttles and its abundant on the surface of the moon. We also believe that there could be ... a tremendous amount of value in precious metals on the surface of the moon. We hear about 'rare Earth metals' – rare Earth metals are not Earth metals. Platinum groups metals – these are metals that are impacts, asteroid impacts from space from billions of years ago."

Finally, Bridenstine talked about the agency's long-term ambition of putting astronauts on Mars, which he expects will happen sometime after 2030. He said Trump has not told him to get humans to Mars "whatever it takes," although the president is "very interested" in accelerating NASA's plans for the red planet. He believes there's still a chance that of finding living organisms on Mars.

"I'm here to say I think that the probability is going up that we could find life on another world, namely Mars," Bridenstine said. "That would be an amazing discovery and I think its important that the United States of America make that discovery."