The four astronauts who flew around the moon on NASA’s Artemis II mission are nearly home, but one of the most dangerous and nerve-racking parts of the mission is still ahead.<\/p>\n\n\n\n
NASA astronauts Reid Wiseman, Christina Koch and Victor Glover and Canadian astronaut Jeremy Hansen are set to return to Earth on Friday evening after 10 days in space.<\/p>\n\n\n\n
Their Orion capsule is scheduled to begin plunging through the atmosphere at around 7:53 p.m. ET on a fiery journey expected to last less than 15 minutes. If all goes well, the mission will culminate in a splashdown in the Pacific Ocean at 8:07 p.m. ET off San Diego.<\/p>\n\n\n\n
\u201cIt\u2019s 13 minutes of things that have to go right,\u201d Jeff Radigan, NASA\u2019s Artemis II flight director, said Thursday at a news briefing.<\/p>\n\n\n\n
Re-entry is always one of the riskiest parts of spaceflight, as vehicles can be exposed to temperatures of around 5,000 degrees Fahrenheit as they streak through the atmosphere. But that is particularly true for Artemis II, because the Orion spacecraft’s heat shield \u2014 the critical layer of thermal protection at the bottom that protects astronauts from extreme temperatures \u2014 has known flaws in its design.<\/p>\n\n\n\n
This mission is the first time the capsule is carrying a crew.<\/p>\n\n\n\n
After the Artemis I mission in 2022 \u2014 an uncrewed test flight of the Space Launch System rocket and Orion capsule \u2014 NASA found unexpected damage to the spacecraft\u2019s heat shield.<\/p>\n\n\n\n
An agency investigation later found that part of the heat shield\u2019s material had cracked during atmospheric re-entry, \u201ccausing some charred material to break off in several locations.\u201d The investigation determined that gases did not vent properly in the heat shield\u2019s outer material, allowing pressure to accumulate, which caused the observed damage.<\/p>\n\n\n\n
Because of those issues, NASA will modify the heat shield design for future Artemis flights. The Orion spacecraft used for those missions will feature a more permeable layer of outer material. But for Artemis II, the capsule had already been built and assembled when NASA learned of the damage sustained during Artemis I.<\/p>\n\n\n\n
So, rather than redo the heat shield, NASA came up with a modified path for the capsule\u2019s re-entry to minimize risk to the astronauts. Ordinarily, before it begins its final descent, the Orion spacecraft is meant to dip into the atmosphere, then pop up again \u2014 like a stone skipping on the water\u2019s surface \u2014 to reduce heat stress and G-force on the capsule. But Amit Kshatriya, NASA\u2019s associate administrator, said that this time the \u201cskip\u201d will be brief and the capsule will descend faster and at a steeper angle to minimize how long it is exposed to the most extreme temperatures.<\/p>\n\n\n\n
\u201cEvery system we\u2019ve demonstrated over the past nine days \u2014 life support, navigation, propulsion, communications \u2014 all of it depends on the final minutes of flight,\u201d Kshatriya said at Thursday\u2019s briefing.<\/p>\n\n\n\n
He added that NASA has \u201chigh confidence\u201d in the spacecraft\u2019s heat shield on the modified path.<\/p>\n\n\n\n
Still, there are significant risks \u2014 and four lives are on the line.<\/p>\n\n\n\n
Charlie Camarda, a former NASA astronaut, has publicly expressed concerns about the heat shield and said NASA should not have launched the Artemis II mission with the existing design.<\/p>\n\n\n\n
“History shows accidents occur when organizations convince themselves they understand problems they do not. This issue exhibits the same patterns that preceded past catastrophes,” he wrote in an open letter to NASA Administrator Jared Isaacman in January.<\/p>\n\n\n\n
Isaacman said that month, however, that he has \u201cfull confidence\u201d in Orion\u2019s heat shield.<\/p>\n\n\n\n
Wiseman, too, has said he is comfortable with the plan.<\/p>\n\n\n\n
\u201cIf we stick to the new re-entry path that NASA has planned, then this heat shield will be safe to fly,\u201d he said during a preflight media event in July.<\/p>\n\n\n\n
The re-entry plan requires the Orion capsule to remain on an extremely precise path, Radigan said. Mission controllers spent the past day and a half keeping the Orion spacecraft on course for that, performing necessary engine burns to maintain its trajectory.<\/p>\n\n\n\n
\u201cLet\u2019s not beat around the bush,\u201d Radigan said. \u201cWe have to hit that angle correctly. Otherwise, we\u2019re not going to have a successful re-entry.\u201d<\/p>\n\n\n\n
During atmospheric re-entry, the Orion capsule is expected to reach an estimated maximum velocity of nearly 24,000 mph. The astronauts will be exposed to G forces equivalent to around 3.9 times the normal pull of Earth\u2019s gravity.<\/p>\n\n\n\n
As the capsule plunges through the atmosphere, a communications blackout is anticipated as plasma builds up around the spacecraft and causes interference. The blackout is expected to last around six minutes, flight director Rick Henfling said at a briefing Wednesday.<\/p>\n\n\n\n
\u201cOnce that six-minute blackout is done, Orion is going to be at about 150,000 feet, so still falling pretty quickly,\u201d he said.<\/p>\n\n\n\n
At an altitude of about 6,000 feet, the capsule will deploy its three main parachutes, which will help slow it down to around 20 mph before it splashes down in the ocean.<\/p>\n\n\n\n
The U.S. Navy will assist with recovery efforts in the Pacific. Once the landing area is deemed safe, NASA\u2019s plan is to extract Koch from the capsule first, then Glover, followed by Hansen and then Wiseman.<\/p>\n\n\n\n
At the briefing Thursday, Kshatriya praised the crew members and said it\u2019s time for flight directors, engineers and recovery teams to bring them home.<\/p>\n\n\n\n
\u201cThe crew has done their part,\u201d he said. \u201cNow we have to do ours.\u201d<\/p>\n\n\n\n