Updated at 2:37 p.m. ET on December 11, 2022
If you want to send people to the moon, you have to be able to bring them home safely. And if you want to bring them home, you must send them hurtling through Earth’s atmosphere in a wash of heat and fire.
An incoming capsule exits space at thousands of miles per hour, then decelerates rapidly. The astronauts inside feel gravity reassert itself with an uncomfortable crush. Friction between the blazing capsule and the surrounding atmosphere produces heat scorching enough to break apart air molecules, and the resulting flashes of plasma fill up the windows, blocking the view of Earth. Some of the heat shield, coated in an inches-thick layer of resin meant to protect the precious cargo against the worst of the fiery conditions, vaporizes.
A NASA spacecraft made this intense ride today, successfully landing in the Pacific Ocean after a long and lonely trek around the moon. The capsule, Orion, launched on NASA’s new moon rocket last month and is a central part of the Artemis program, America’s effort to put astronauts on the lunar surface for the first time in 50 years. No astronauts were on board this time, but NASA proved that it can bring the capsule home in one piece.
With this splashdown, engineers pulled off a long-dreamed-of revolution of reentry: Rather than plummeting as soon as spacecraft met sky, the capsule skipped across the atmosphere like a rock on the surface of a lake before committing to the plunge. Wild as that may sound, the maneuver is meant to be more efficient and safe. With this test of its fancy new reentry technique, NASA has shown that it’s ready not only to send people to the moon again in the 21st-century version of the Apollo program but also to bring them home.
Ask an engineer which part of spaceflight is the most difficult, and they’ll say all of them; it is rocket science, after all. But reentry carries certain dangers that other steps do not. Sitting atop a bunch of explosives during takeoff is certainly a risk, but if a rocket malfunctions in the moments after launch, at least Orion can jettison itself away. Once the capsule starts falling back to Earth in earnest, all it can do is keep falling; “you have to get through to reach the ground,” Jim Geffre, a NASA manager for the Orion program, told me. Mission control can’t stay in contact with a crew the whole way down; the surrounding plasma produces a brief communications blackout. Plus, the slightest flaw in a spacecraft’s heat shield can spell disaster. The second and final tragedy in NASA’s space-shuttle program, in 2003, occurred when the ship’s heat shield, damaged days earlier during launch, failed to hold upon reentry, and the ship was destroyed.
The Orion capsule uses the same resin material on its heat shield as the Apollo hardware, only applied in a new way. And future Artemis astronauts will land as the Apollo corps did, parachuting to open water, where recovery crews will tug them to safety. Orion has flown to space and back in a previous, skip-free test, but it did not go as far as the moon, which means it reentered the atmosphere at a cool 20,000 miles per hour. This time, Orion came barreling in at 25,000 miles per hour. It slowed as it sailed through the atmosphere, feeling the drag of increasing air density. But as it traveled, the specially designed capsule also generated its own lift, and it used that lift to leap up out of the atmosphere and back to space. Then, when it was ready, Orion dived back in for the final descent.
The “skip entry,” as the technique is called, let Orion spend more time flying through the atmosphere, which in turn allowed the vehicle to target its landing site with more precision. Future capsules can land in the same place, regardless of where they first skimmed the atmosphere, and ships can get to them faster, which will keep astronauts safer. In the Apollo days, the U.S. stationed Navy ships in several locations in the Pacific, ready to sail to the spot the capsule wound up in. The Artemis days will require far fewer Navy resources, saving all parties some money. The atmospheric bounce also splits the effects of the fiery reentry into two occasions, rather than one blazing phase, so the capsule’s heat shield doesn’t need to withstand conditions that are quite as intense.
Apollo engineers knew all about the magic of the skip entry, Kelly Smith, a former Orion engineer who left NASA last year, told me. They just couldn’t make it work with 1960s technology. Computers weren’t powerful enough to calculate the precise atmospheric flight mechanics involved in the maneuver, and the skip-entry method is so sensitive that approximations don’t cut it, so NASA didn’t dare try skipping a capsule, crewed or not. With today’s computing chops, “we can nail it,” Smith said. “We’ve been able to supercharge the original Apollo algorithms and make this work really reliably.”
As with any aspect of spaceflight, skip entry is not without its risks. “You do fly longer through the atmosphere,” which prolongs the heat shield’s exposure to scorching conditions, Geffre said. And capsules could potentially botch the skip, falling short of their intended touchdown site, and leave astronauts stranded for longer than anticipated. Engineers have run countless skip simulations, but simulations are “a poor substitute for the real world,” Smith said. Several hundred thousand feet above Earth, in that ephemeral region between us and outer space, “Isaac Newton is really at the steering wheel.” Ending up in the wrong spot is “really undesirable when you have people on board,” Smith said. “It’s not at all enjoyable to be bobbing around in the ocean.”
It will be a while before anyone is bobbing inside an Orion capsule, fresh off a moon visit. The Artemis program’s first crewed mission is scheduled for late 2024, and that flight won’t actually involve a lunar landing; rather, it will loop around the moon, like Apollo 8 in 1968. This century’s Apollo 11 will come sometime later this decade.
When the Apollo 8 astronauts came home, they were bracing for impact. “There’s no turning back now,” Bill Anders said in the moments before reentry. “Old Mother Earth has us,” Jim Lovell added. The Artemis crew will feel gravity bearing down on them too—but then they’ll feel the skip, a sudden, temporary return to weightlessness, by then a familiar sensation to them, after their long journey beyond Earth.
This article originally misstated the speed at which Orion reentered the atmosphere during an earlier test flight.