SpaceX has signed a 2.99 billion ($ 3.75 billion) deal to build a spacecraft that will land astronauts on the moon for the first time in five decades.

The fixed-price deal is a big vote of confidence for Elon Musk’s rocket company, as the space agency is largely responsible for its ground-based human spaceflight program, known as Artemis in SpaceX.

Friday’s announcement offered Blue Origin, a rocket company founded by Jeff Bezos, to design and build a lunar lander as part of a “national team” alongside corporate behemoths such as Northrop Grumman and Lockheed Martin, and Alabama-based Dynetics, which had its bids.

But SpaceX had won a bid to use a spacecraft, and the company was already developing its own in South Texas.

The vehicle, also known as the Starship, is also the linchpin of Mr. Musk’s personal goal for the first man to land on Mars. Test flights of early Starship prototypes have so far ended in explosions, but the company is rapidly building new test vehicles.

Last year, NASA announced three separate agreements for the development of the Moon Lander, which were awarded to the “national team” of SpaceX and Blue Origin, with the expectation that the companies would each work to bring operational vehicles to succeed and compete with each other in price and technology.

Lisa Watson-Morgan, NASA’s Human Landing System or HLS program manager, said in a press call on Friday that NASA supported all contractors at that stage who provided “design support analysis, subject matter expertise and testing.”

Ms. Watson-Morgan added that NASA will continue to provide intensive monitoring as SpaceX continues to evolve, “ensuring this system will be safe for our astronauts.”

Boeing is building another key component for the Artemis program: the space launch system, or SLS, a giant rocket designed to carry Orion crew capsules to the moon. This is the rocket that will take the astronauts to lunar orbit and then transfer the crew to the Gateway Space Station and from there the starship will take the astronauts to the moon, said Mrs. Watson-Morgan.

The SLS development program is behind a multi-billion dollar budget and schedule.

NASA says SpaceX will have to conduct an immediate demonstration mission to land a starship on the moon before astronauts will fly onboard.

The astonishing announcement on Friday that SpaceX would be the only prize came after the space agency fought for two years after forcing Congress to provide adequate funding for the Moon Lander Development Program.