NASA astronaut and Artemis II mission specialist Christina Koch peers out of one of the Orion spacecraft’s main cabin windows, looking back at Earth, April 2.NASA/Reuters
Before the crew of NASA’s Artemis II mission is safely back on Earth, they have one more milestone to overcome, and it’s a big one.
While hurtling toward the planet at more than 38,000 kilometres an hour, their spacecraft, named Integrity, has to survive a 13-minute high-speed descent through Earth’s atmosphere. If all goes well, that will slow it down enough to deploy parachutes and bring it to a splashdown in the Pacific Ocean about 8:07 p.m. ET on Friday.
The Artemis II crew embraces inside their spacecraft on the way home from a flyby of the far side of the moon on Tuesday.NASA/Reuters
Like the moon mission itself, it’s a feat that people have not attempted since the early 1970s. And it will depend crucially on a sequence of pre-determined steps that need to work to ensure the crew’s survival.
The four crew members – Reid Wiseman, Victor Glover, Christina Koch and Canadian astronaut Jeremy Hansen – left Earth on April 1. By the time they return, they will have been in space for more than nine days, after executing a memorable loop around the moon’s far side and experiencing a solar eclipse from space.
Artemis II astronauts talk inspiration and teamwork in call with Mark Carney
At a Thursday mission status briefing at the Johnson Space Center in Houston, NASA associate administrator Amit Kshatriya did not mince words about the need for things to go right during the mission’s final moments.
“Every system we’ve demonstrated over the past nine days – life support, navigation, propulsion, communications – all of it depends on the final minutes of flight,” he said.
He added that NASA has high confidence in the multipart procedure that was designed, built and tested to bring the capsule down to Earth, “and tomorrow the crew’s going to put their lives behind that confidence.”
Returning from space is something astronauts have been doing for years, whenever a crew completes a stint on board the International Space Station. But arriving from low Earth orbit, where the station is located, is not as rapid a process nor as demanding on the structure of a spacecraft as an incoming flight from the moon.
And it is surely top of mind for engineers that the crew capsule’s heat shield did not perform as well as expected on its first and only test flight, which flew without astronauts on board.
Heat endurance presents a key challenge for Integrity as it rips through the air like a meteor during its final descent.
Weighing in at 9.3 tonnes, the capsule is nearly twice the mass of the Apollo command modules of the past. That means more energy in the form of air friction will be needed to slow it down. At maximum deceleration, the capsule’s heat shield is expected to experience temperatures in excess of 2,700 C.
Prime Minister Mark Carney had a video call with the astronauts on Artemis II, and as he quickly learned, the lag is real when you’re talking to space. Speaking primarily with mission specialist Jeremy Hansen, who is Canadian, Carney commended the crew on their bravery, their willingness to take risks and to learn from failure, especially for the young people watching. The planned splashdown for Artemis II is on Friday.
Following the Artemis I test flight of an empty version of the Orion crew capsule in 2022, engineers discovered the capsule’s heat shield sustained more damage than expected. The heat shield material, called AVCOAT, consists of silica fibres in an epoxy resin, which is meant to burn away evenly as the spacecraft descends. Instead, entire chunks of the shield fell off during re-entry.
The capsule survived but the way the shield responded to heating was cause for alarm. A technical investigation into what happened was the primary reason why the launch of Artemis II was ultimately delayed for more than a year.
Engineers determined that the problem was owing to a novel re-entry trajectory that Artemis I demonstrated during its return. Known as a “skip re-entry,” it involved the spacecraft striking the atmosphere at a shallow angle and bouncing up again before resuming its descent, like a stone skipping on a pond.
The point of this manoeuvre was to increase the accuracy of the capsule’s downward path and allow it to splash down closer to shore. But the double dip proved to be a problem because air bubbles that formed during the initial heating then caused the heat shield to fall apart more easily after the skip.
Since the capsule for Artemis II was already built by then, NASA decided to alter the skip manoeuvre and instead bring the capsule in on a steeper path. Later missions, starting with Artemis III, will feature a redesigned heat shield to eliminate the hazard.
But the change means that the crew of Artemis II will be in for a rather dramatic ride, including anticipated forces of 3.9 G, as they transition from space back to Earth.
A photo provided by NASA shows technicians inspecting the Artemis II heat shield at the Kennedy Space Center in Florida in 2020.ISAAC WATSON/The New York Times
Prior to re-entry on Friday, NASA will adjust the course of the spacecraft to keep it on target for a splashdown off the coast of California near San Diego.
Ahead of re-entry, the crew will have completed stowing away equipment from their mission and will again be in the orange-coloured spacesuits they wore during launch. They’ll also strap themselves back into their seats while Earth looms ever larger in their view ports.
At 42 minutes before splashdown, the service module that contains Integrity’s main propulsion system and solar panels is meant to separate and burn up on its way down to the Pacific. Shortly after, the remaining crew module will execute a “raise burn” to move to a higher trajectory that is clear of the service module and also rotate so that its heat shield is facing the direction of travel. About 13 minutes before splashdown, the spacecraft will begin to feel Earth’s atmosphere.
“That’s when the fun really begins,” said Rick Henfling, who is flight director for the re-entry portion of the mission.
At this point the crew will be in a communications blackout as the capsule is enveloped in superheated plasma.
From Vaughan to the moon: Starry-eyed superfan tracks the Artemis II lunar mission
Upon emerging from blackout, a protective top cover on the capsule will be jettisoned so that parachutes can be deployed. These come out in sequence to help slow the capsule further until the three main parachutes open at about 1.8 kilometres above the water.
By the time the capsule splashes down, it should be dropping at the leisurely speed of about 27 kilometres an hour, with astronauts ready to be picked up by a navy team on a ship close by.
So far weather conditions are favourable for the event, Artemis II lead flight director Jeff Radigan said at Thursday’s briefing.
Asked what he told the crew when he signed off on his final shift of the mission, Mr. Radigan said it was with the same words he always does: “Get some sleep and we’ll see you tomorrow.”