The Artemis I mission - a 25-day uncrewed test flight around the moon meant to pave the way for future astronaut missions - came to an momentous end as NASA's Orion spacecraft made a successful ocean splashdown Sunday, CNN reported.
The spacecraft finished the final stretch of its journey, closing in on the thick inner layer of Earth's atmosphere after traversing 239,000 miles (385,000 kilometers) between the moon and Earth. It splashed down at 12:40 p.m. ET Sunday in the Pacific Ocean off Mexico's Baja California.
Rob Navias, the NASA commentator who led Sunday's broadcast, called the reentry process "textbook."
This final step was among the most important and dangerous legs of the mission.
"We're not out of the woods yet. The next big test is the heat shield," NASA Administrator Bill Nelson had told CNN in a phone interview Thursday, referring to the barrier designed to protect the Orion capsule from the excruciating physics of reentering the Earth's atmosphere.
The spacecraft was traveling about 32 times the speed of sound (24,850 miles per hour or nearly 40,000 kilometers per hour) as it hit the air - so fast that compression waves caused the outside of the vehicle to heat to about 5,000 degrees Fahrenheit (2,760 degrees Celsius). The extreme heat also caused air molecules to ionize, creating a buildup of plasma that's expected to cause a 5-minute communications blackout, according to Artemis I flight director Judd Frieling.
WATCH | What does skip entry mean to bring capsule back to earth
As the capsule reached around 200,000 feet (61,000 meters) above the Earth's surface, it performed a roll maneuver that briefly sent the capsule back upward - sort of like skipping a rock across the surface of a lake.
There are a couple of reasons for using the skip maneuver.
"Skip entry gives us a consistent landing site that supports astronaut safety because it allows teams on the ground to better and faster coordinate recovery efforts," said Joe Bomba, Lockheed Martin's Orion aerosciences aerothermal lead, in a statement. Lockheed is NASA's primary contractor for the Orion spacecraft.
"By dividing the heat and force of reentry into two events, skip entry also offers benefits like lessening the g-forces astronauts are subject to," according to Lockheed, referring to the crushing forces humans experience during spaceflight.
As it embarked on its final descent, the capsule slowed down drastically, shedding thousands of miles per hour in speed until its parachutes deploy. By the time it splashed down, Orion was traveling about 20 miles per hour (32 kilometers per hour).
While there were no astronauts on this test mission - just a few mannequins equipped to gather data and a Snoopy doll - Nelson, the NASA chief, has stressed the importance of demonstrating that the capsule can make a safe return.
The space agency's plans are to parlay the Artemis moon missions into a program that will send astronauts to Mars, a journey that will have a much faster and more daring reentry process.
Orion traveled roughly 1.3 million miles (2 million kilometers) during this mission on a path that swung out to a distant lunar orbit, carrying the capsule farther than any spacecraft designed to carry humans has ever traveled.
A secondary goal of this mission was for Orion's service module, a cylindrical attachment at the bottom of the spacecraft, to deploy 10 small satellites. But at least four of those satellites failed after being jettisoned into orbit, including a miniature lunar lander developed in Japan and one of NASA's own payload that was intended to be one of the first tiny satellites to explore interplanetary space.
On its trip, the spacecraft captured stunning pictures of Earth and, during two close flybys, images of the lunar surface and a mesmerizing "Earth rise."
Nelson said if he had to give the Artemis I mission a letter grade so far, it would be an A.
"Not an A-plus, simply because we expect things to go wrong. And the good news is that when they do go wrong, NASA knows how to fix them," Nelson said. But "if I'm a schoolteacher, I would give it an A-plus."
With the success of the Artemis I mission, NASA will now dive into the data collected on this flight and look to choose a crew for the Artemis II mission, which could take off in 2024.
Artemis II will aim to send astronauts on a similar trajectory as Artemis I, flying around the moon but not landing on its surface.
The Artemis III mission, currently slated for a 2025 launch, is expected to put boots back on the moon, and NASA officials have said it will include the first woman and first person of color to achieve such a milestone.
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