NASA picked a very good morning to return from the moon. It was 50 years ago today that the crew of Apollo 17 landed in the Taurus Littrow Valley on the lunar surface, where they planted the last of six flags Apollo crews would leave behind to mark their moments in history. Today, the space agency planted a new, if symbolic flag, when the Artemis 1 mission’s Orion crew capsule splashed down in the Pacific Ocean 320 km (200 mi.) off the coast of Baja California, Mexico, at 9:40 a.m. Pacific Time. The safe return marked the end of a 25-day lunar orbital mission, proving the flight-worthiness of the Orion spacecraft, which is expected to carry a crew of astronauts on a circumlunar journey during Artemis 2, in 2024.
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“Splashdown,” NASA tweeted, seconds after the spacecraft hit the water. “After traveling 1.4 million miles through space, orbiting the Moon, and collecting data that will prepare us to send astronauts on future #Artemis missions, the @NASA_Orion spacecraft is home.
The recovery of Orion was expected to be smooth and without incident—“nominal,” as NASA puts these things. The Navy’s USS Portland was in the splashdown site—just 8 km (5 mi.) away; after the capsule hit the water, a five-hour process got underway in which a recovery team left the ship aboard small boats, headed for Orion. There, the plan calls for them to attach cables to the spacecraft and tow it back to the Portland, where, a winch line and four supporting cables were waiting to lift Orion up to the deck of the ship.
“Last week, we completed our final rehearsal with the USS Portland,” said Melissa Jones, NASA’s landing and recovery director, in a Dec. 5 statement. “We had a great three days working with them to refine our procedures and integrate our teams.”
The mission the spacecraft flew was an ambitious one, beginning with the Nov. 16 launch of NASA’s much-delayed Space Launch System (SLS) moon rocket—a machine that, with its 4 million kg (8.8 million lbs) of thrust, is the most powerful rocket ever launched. The Orion spacecraft took five days to reach the vicinity of the moon, then fired its engine to brake its speed slightly and enter lunar orbit. It spent the next two weeks making two wide, looping circuits around the moon, twice passing as close as 129 km (80 mi.) from the surface. At its most distant remove, the ship was more than 431,000 km (268,000 mi.) from Earth, and 69,000 km (43,000 mi.) above the far side of the moon. That broke the 400,000 km (250,000 mi.) distance record for a crew-rated spacecraft set by Apollo 13 during its one pass around the far side of the moon in 1970.
On Dec. 5, with its two lunar orbits complete, Orion fired its main engine for 3 minutes and 27 seconds, increasing its speed by 1,054 km/h (655 mph), which gave it enough propulsive muscle to pull away from the moon’s gravitational influence and head for home. The coast back to Earth was entirely nominal too. It was only when the spacecraft approached the planet that things got more complicated.
Orion was flying at about 40,000 km/h (25,000 mph) when it slammed into the atmosphere, beginning a plunge that would ultimately cause its heat shield to withstand temperatures of 2,760º C (5,000º F). During its descent it successfully pulled off a never-before-tried maneuver known as a “skip entry.”
The spacecraft initially plunged to an altitude of 61,000 m (200,000 ft.)—or about 61 km (38 mi.). Then it rolled 180 degrees—so that future astronauts who were sitting straight up inside would now be upside down—changing its center of gravity. That caused the ship to skip off the atmosphere and bounce back up to 99,000 m (325,000 ft)—or 99 km (61 mi)—essentially back into space. After that parabolic maneuver, Orion resumed its descent, with its guidance system pointing it straight for the waters off Baja California.
The skip entry served two key purposes. For one thing, the Apollo astronauts had to endure forces of 6.8 g’s (or 6.8 times Earth’s gravity) during their reentries, before their speed slowed, their parachutes opened, and they hit the water. The skip entry’s gentle parabolic flight will reduce the g-forces for future astronauts to just 4.
Just as important, taking a bead on the ground from that 99 km altitude during the skip part of the maneuver allows the spacecraft’s guidance system to direct the capsule to a pretty much pinpoint landing anywhere within an 8,890 km (5,524 mi) range. That means a closer-to-home, daylight landing like the one Orion made, as compared to the splashdowns of the Apollo crews, who were much more limited in the choice of landing sites and times. Apollo 8, for example, landed in the Pacific Ocean in pre-dawn darkness, in an area where sharks were known to feed before sun-up. The crew had to wait in their stultifyingly warm spacecraft in choppy Pacific waters until it was light enough for Navy frogmen to arrive on the scene for the recovery.
With Artemis 1 successfully in the books, NASA can set about selecting a crew and beginning their training for Artemis 2—just two years away. After that, likely no earlier than 2026, Artemis 3 will return astronauts to the lunar surface—adding a seventh flag to the half dozen still standing there.
