If you want to send people to the moon, you have to be able to bring them home safely. You must also send them through Earth’s atmosphere on a wave of heat and flame to get them back. An incoming capsule leaves space at thousands miles an hour and then slows down. Gravitation is felt by the astronauts in it with a painful 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. The heat shield is covered in a thick layer of resin to protect precious cargo from the most extreme fiery conditions. Some of it vaporizes. A NASA spacecraft successfully landed in the Pacific Ocean today after an exhausting journey 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 achieved a long-awaited revolution in reentry. Instead of the capsule plummeting from the moment it met the sky, the capsule sailed across the atmosphere as if it were a rock floating on the lake’s surface before taking 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. The capsule will begin to fall back towards Earth once it starts. “You have to get through” Jim Geffre told me. Because of the plasma surrounding the capsule, mission control is unable to keep in touch with crew members the entire way. The smallest flaws in the heat shield of a spacecraft can lead to 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. Future Artemis astronauts will parachut to open waters, and then be rescued by recovery crews. 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 17,500 miles per hour, the same as any spaceship that visits a destination in Earth orbit, such as the International Space Station. This time, Orion came barreling in at 25,000 miles per hour. As it passed through the atmosphere, Orion slowed down and felt the pull of the 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” technique allowed Orion to spend more time in the atmosphere. This enabled the vehicle more precisely target its landing spot. 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. Because the atmospheric bounce splits the fiery-reentry effects into two phases, instead of one, the heat shield for the capsule doesn’t have to be able to withstand as extreme conditions. Kelly Smith (ex-Orion engineer, who left NASA last January) told me that
Apollo engineers were well aware of the wonders of skip entry. They just couldn’t make it work with 1960s technology. The orbital mechanics of the maneuver were too complex for computers to compute. Also, the skip-entry technique is so precise that even approximates won’t work. NASA decided not to attempt to skip a crewed capsule. Smith stated that “we can nail” the task with today’s computer skills. “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. Geffre stated that “you fly further through the atmosphere,” which increases the shield’s heat exposure. Capsules can also fail to land at their destination, leaving astronauts without power for much longer. Smith stated that engineers have done many skip simulations but they are not a good substitute for real life. Smith stated that it is not at all enjoyable to be bobbing around in the ocean. “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.