Houston-based Intuitive Machines readied its Odysseus lander for touchdown on the moon today, a nail-biting one-hour 13-minute descent from orbit to become the first U.S.-built spacecraft to stick a moon landing in more than 50 years and the first ever by a private company.

One day after braking into a 57-mile-high orbit tilted 80 degrees to the moon’s equator, Odysseus’ methane-fueled main engine was primed to ignite at 4:17 p.m. EST, lowering the far side of the orbit to a point near the landing site some 186 miles from the moon’s south pole.

As the 14-foot-tall spacecraft descends toward the surface, on-board cameras and lasers are programmed to scan the ground below to identify landmarks, providing steering inputs to the lander’s guidance system to help fine tune the trajectory.

One hour later, at 5:18 p.m., the main engine is expected to ignite again at an altitude of about 18 miles and to keep firing for the final 10 minutes of the descent, flipping Odysseus from a horizontal orientation to vertical and dropping straight down at just under 4 mph.

As the spacecraft drops below 100 feet, an innovative camera package, known as “EagleCam,” built by students at Embry-Riddle Aeronautical University, will fall away and attempt to photograph the lander’s final descent from the side. NASA cameras on board the spacecraft will photograph the ground directly below.

By the time Odysseus reaches an altitude of about 33 feet above the surface, the main engine was to have throttled down to the planned landing velocity of about 2.2 mph — walking speed for senior citizens.

Touchdown near a crater known as Malapert A is expected at 5:30 p.m., one week after launch from the Kennedy Space Center.

Video from the lander’s on-board cameras and the EagleCam cannot be transmitted back to Earth in real time, but Intuitive Machines’ engineers at the company’s Nova Control center in Houston say they should be able to verify touchdown within about 15 seconds. The first pictures are expected within a half hour or so.

A successful lunar landing would mark the first touchdown by a U.S.-built spacecraft since the Apollo 17 mission in 1972 and the first ever by a privately-built spacecraft.

Pittsburg-based Astrobotic hoped to claim that honor last month with its Peregrine lander, but the mission was derailed by a ruptured propellant tank shortly after launch Jan. 9. Two earlier private moon ventures, one by Israel and the other by Japan, also ended in failure.

Only the governments of the United States, Russia, China, India and Japan have successfully put landers on the surface of the moon, and Japan’s “SLIM” lander was only partially successful, tipping over on touchdown Jan. 19.

Peregrine and Odysseus were both funded in part by NASA’s Commercial Lunar Payload Services program, or CLPS (pronounced CLIPS), designed to encourage private industry to develop transportation capabilities that NASA can then use to transport payloads to the moon.

The agency’s goal is to help kickstart development of new technologies and to collect data that will be needed by Artemis astronauts planning to land near the moon’s south pole later this decade.

NASA paid Astrobotic $108 million for its part in the Peregrine mission and another $129 million for the Odysseus instruments and transportation to the moon.

What’s on board the Odysseus moon lander?

Odysseus was equipped with six NASA instruments and another six commercial payloads, including small moon sculptures by the artist Jeff Koons, proof-of-concept cloud storage technology, Columbia Sportswear insulation blankets and a small astronomical telescope.

Among the NASA experiments: an instrument to study the charged particle environment at the moon’s surface, another designed to test navigation technologies and the downward-facing cameras designed to photograph how the lander’s engine exhaust disrupts the soil at the landing site.

Also on board: an innovative sensor using radio waves to accurately determine how much cryogenic propellant is left in a tank in the weightless environment of space, technology expected to prove useful for downstream moon missions and other deep space voyages.

Odysseus and its instruments are expected to operate on the surface for about a week, until the sun sets at the landing site. At that point, the lander’s solar cells will no longer be able to generate power and the spacecraft will shut down. Odysseus was not designed to survive the ultra-cold lunar night.