Orion set several records during the Artemis 1 mission to the Moon, in addition to surviving 5,000 degree Fahrenheit temperatures during atmospheric re-entry. The spacecraft’s innovative heat shield made this possible, but NASA’s follow-up analysis of the protective layer has revealed levels of wear and aging that were not predicted by models.
“Orion exceeded all performance expectations,” Howard Hu, head of the Orion program, told reporters yesterday at a NASA briefing to discuss the latest Artemis 1 results. Over 160 flight test targets were achieved, with 21 added during the mission as managers got “better than expected performance,” he said. That unmanned Orion capsule splashed down in the Pacific Ocean on December 11, 2022 after a 26-day trip to the Moon and back.
During inspections and analysis, however, the investigators noticed some unexpected variations across Orion’s heat shield. “Some of the charred material ablated differently than our computer models and our soil tests predicted,” Hu said. “More of this charred material was released during reentry than we expected.”
A dedicated investigation has been launched into the matter, and while NASA is “working hard to learn more about this,” overall there is a lot “a lot of work to be done in this investigation moving forward,” he explained, adding that it’s a big task of correlating the associated data. It’s not immediately clear how much more charred material came off than expected — “that’s the analysis we have to do,” Hu said. Investigators must individually examine each heat shield block, of which there are more than 180.
Orion is intended to carry astronauts, but the unexpected performance is not a safety concern, according to Hu. He said a “significant amount of margin” remained and he “doesn’t think we reached any limits from a margin perspective.” The protective heat shield did its job and then some, but because this behavior was not predicted by models, it is something NASA must now investigate. NASA wants to make sure it has the best possible heat shield to protect human passengers during future missions, Hu explained.
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Returning from the Moon, Orion entered Earth’s atmosphere at speeds reaching 24,600 miles per hour (39,590 kilometers per hour). This produced temperatures in excess of 5,000 degrees Fahrenheit, which the heat shield proved capable of handling. The heat shield uses tiles made of an ablative material called Avcoat to protect the capsule and crew during atmospheric reentry. An ablator “burns off in a controlled manner during re-entry and transfers heat away from the spacecraft,” NASA explained in a Dec. 8 Press release. The new Avcoat tiles measure anywhere from 1 to 3 inches thick and cover the outer surface of the heat shield.
Engineers expected some charring of the ablative material, Hu said, but small pieces that came off instead of ablating (i.e., burning off in a controlled way) were a surprise. We would like to understand that, he said.
Despite this problem, NASA officials said the space agency is moving forward with the planned Artemis 2 mission, which will involve a crew of astronauts. Repairs are underway at the launch pad, the new Space Launch System (SLS) rocket is being built, and the next Orion capsule is set for testing as most of it has already been assembled. Like Artemis 1, the Artemis 2 mission will see an Orion capsule journey around the Moon and back, with the big difference being the inclusion of an actual crew.
Speaking to reporters during Tuesday’s briefing, Jim Free, associate administrator for NASA’s Exploration Systems Development Directorate, said preparations for Artemis 2 “continue to move forward” and that now is “the time for our vigilance to continue” , so “we understand the risks we are taking.” Encouragingly, there is nothing in the Artemis 1 post-flight analysis that gives NASA any reason to change its launch date for Artemis 2, which is planned for late November 2024, Free said.
Artemis 3 – a manned mission to the lunar surface – is planned for late 2025, but Free warned that key milestones must be met to make that happen, namely the certification of SpaceX’s Starship mega rocketboth as a launch vehicle and as a lunar lander, in addition to the space agency receiving necessary Moonsuits from Axiom Space.
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