Enlarge / Orion flew by the Moon on Monday as it prepared to return to Earth. (credit: NASA)

NASA's Artemis I mission is nearly complete, and so far Orion's daring flight far beyond the Moon has gone about as well as the space agency could hope. However, to get a passing grade, the mission must still ace its final test.

This final exam will come on Sunday, when the spacecraft starts to enter Earth's atmosphere at 12:20 pm ET (17:20 UTC). During the course of the next 20 minutes, before Orion splashes down in the Pacific Ocean off of Mexico's Baja Peninsula, it will need to slow down from a velocity of Mach 32 to, essentially, zero before dropping into the water.

This is no small feat. Orion has a mass of 9 metric tons, about the same as two or three large elephants. Its base, covered with a heat shield designed to slowly char away during passage through Earth's atmosphere, must withstand temperatures near 3,000 degrees Celsius.

Enlarge / Orion, the Moon, and a crescent Earth on Monday. (credit: NASA)

The Orion spacecraft swung by the Moon on Monday, flying to within 130 km of that world's surface as it set course for a return to Earth this weekend.

In making this "powered flyby burn" to move away from the Moon, Orion's service module performed its longest main engine firing to date, lasting 3 minutes and 27 seconds. After successful completion of the maneuver, NASA's mission management team gave the "go" to send recovery teams out into the Pacific Ocean, where Orion is due to splashdown on Sunday, during the middle of the day.

By getting into an orbit around the Moon, and back out of it again during its deep space mission, Orion has now completed four main propulsive burns. This completes a big test of the spacecraft and its propulsive service module, which was built by the European Space Agency. Although a boilerplate version of Orion made a flight in 2014, it did so without a service module.

Enlarge / The Orion spacecraft approaches the Moon on Monday. (credit: NASA)

So far, NASA's ambitious Artemis I mission seems to be going swimmingly. The Orion spacecraft has performed a number of propulsive burns, flying smoothly past the Moon , and will now test out its capabilities in deep space.

On Monday evening, after flying around the Moon, the spacecraft returned images of the flyby back to Earth via the Deep Space Network. While no humans are on board Orion during this test flight, they will be during its next mission. The views of the Moon from human spacecraft—the first in more than half a century—were brilliant.

"Today was a terrific day," said Howard Hu, program manager for the Orion spacecraft, speaking about the spacecraft's performance and its images. "This is a dream for many of us who work at NASA. We were like kids in a candy store."

Enlarge / NASA's Space Launch System rocket lifts off on Wednesday morning from Kennedy Space Center.

KENNEDY SPACE CENTER, Fla. —The skies were auspicious during the wee hours of Wednesday morning, as the Artemis I mission ticked down its final seconds until liftoff.

Ten, nine, eight seconds ...

Shining brightly, near the southern horizon, was the constellation Orion, namesake to NASA's new deep space vehicle.

Enlarge / NASA's rocket has been rolled out to the launch pad in Florida four times now this year. (credit: Trevor Mahlmann)

KENNEDY SPACE CENTER, Fla.—After writing about NASA's Space Launch System rocket for a dozen years—certainly well into the hundreds of thousands of words—I've run out of things to say about the big, orange booster.

Well, almost . What I would like to say is that it is time, beyond time really, for this mission to fly.

As NASA has sought to build public interest in the Artemis program and spur momentum for the Artemis I launch of an uncrewed Orion spacecraft to the Moon and back, the space agency has increasingly used the slogan, "We are going."

Enlarge / NASA's Space Launch System will make a nighttime launch on its current timeline. (credit: Trevor Mahlmann)

As subtropical storm Nicole moved across the Atlantic Ocean toward Florida on Monday afternoon, NASA confirmed that its Artemis I mission would remain at the launch pad along the state's east coast.

"Based on current forecast data, managers have determined the Space Launch System rocket and Orion will remain at Launch Pad 39B," the agency said .

The risks to these large and costly vehicles are non-zero, however, and appear to be rising as Nicole starts to strengthen. The space agency's primary concern from tropical systems is winds. Much of the rocket's structure is pretty robust, such as its tank-like solid rocket boosters. But there are sensitive elements prone to damage from debris and wearing effects due to high winds inside a tropical system.

Enlarge / NASA's Space Launch System will make a nighttime launch on its current timeline. (credit: Trevor Mahlmann)

A little more than two weeks have passed since NASA prudently rolled its Space Launch System rocket and Orion spacecraft inside the massive Vehicle Assembly Building at Kennedy Space Center to protect the hardware from Hurricane Ian.

During that time, engineers and technicians from the space agency and its contractors have performed a detailed inspection of the rocket and spacecraft to determine its flight readiness. This was an important process because the vehicles have been in a fully stacked configuration for nearly a year, since October 21, 2021. NASA wanted to assess the ongoing viability of batteries on the rocket, hypergolic fuel stored on Orion's service module, and more.

The good news from those inspections is that only minimal work is required to prepare the rocket for its next launch attempt, NASA said Wednesday in a blog post .

Enlarge / The fully stacked Space Launch System rocket and Orion spacecraft will roll back to the Vehicle Assembly Building on Monday night. (credit: Trevor Mahlmann)

After delaying a final decision for two days, NASA on Monday made the call to roll its massive Space Launch System rocket and Orion spacecraft inside the Vehicle Assembly Building (VAB) at Kennedy Space Center in Florida.

The space agency took this precautionary step as the storm Ian intensified into a hurricane in the Caribbean Sea and remained on track to move into the southeastern Gulf of Mexico on Tuesday.

"Managers met Monday morning and made the decision based on the latest weather predictions associated with Hurricane Ian, after additional data gathered overnight did not show improving expected conditions for the Kennedy Space Center area," NASA said in a blog post . "The decision allows time for employees to address the needs of their families and protect the integrated rocket and spacecraft system."