NASA aims to have the Space Launch System rocket ready for the Artemis II mission, the first manned flight around the moon since 1972, sometime next month. But the agency's head of exploration says the milestone could be delayed as engineers continue to assess the readiness of the Orion spacecraft's heat shield.
The heat shield, already installed at the base of the Orion spacecraft, will take the brunt of the heat as the capsule hurtles through Earth’s atmosphere at the end of its 10-day mission. During the Artemis I test flight in late 2022, NASA sent an Orion spacecraft to the moon and back without a crew on board. The only significant blight on the test flight was the discovery that charred chunks of the heat shield unexpectedly fell off the capsule during re-entry, when temperatures soared to nearly 5,000 degrees Fahrenheit (2,760 degrees Celsius).
The spacecraft landed safely, and if astronauts had been on board, it would have been fine. However, inspections of the recovered spacecraft revealed that holes in the heat shield material were missing. The heat shield material, called Avcoat, is designed to erode away in a controlled manner during reentry. Instead, fragments of the heat shield fell away, creating cavities that looked like pits.
“There is still a lot of work to be done”
NASA launched internal and independent investigations to look into the heat shield issue. Catherine Koerner, NASA's associate administrator for exploration systems development, told Ars that the investigation remains open.
“We haven't made any formal decisions about the path forward because we're still doing analyses,” she said. “There are a lot of complications associated with the heat shield, not only with identifying a root cause, but also with determining a path forward once we've identified that root cause.”
It’s a complicated thermodynamic and aerodynamic problem, with engineers studying the combined effects of heating and drag as the Orion spacecraft plunges deeper into the atmosphere. Victor Glover, the pilot of the Artemis II mission, told Ars earlier this year that ground testing and analysis can only go so far, and that some dynamics may not be fully understood without more flight data.
Commander Reid Wiseman, mission specialist Christina Koch and Canadian astronaut Jeremy Hansen will accompany Glover on the Artemis II mission. They will fly around the far side of the moon in the Orion capsule after blasting off from NASA's Kennedy Space Center in Florida aboard a Space Launch System (SLS) rocket. Artemis II will pave the way for future landing missions to take astronauts to the lunar south pole.
But it is taking longer than NASA officials would have liked to complete the investigation into the Orion heat shield. Koerner said she would not estimate how long it would take for NASA to decide what, if any, changes need to be made to the Artemis II mission to reduce the risk to astronauts.
“The best way to ensure crew safety in any operation, but this one in particular, is to make sure they understand that they are doing this – the focus of this investigation and the way forward – with crew safety in mind, and not with schedule pressure or any other kind of external stakeholder pressure,” she said.
Possible solutions to the heat shield problem for Artemis II include changing the spacecraft's trajectory during reentry or making changes to the heat shield itself. The latter option would require the Orion spacecraft to be partially disassembled at NASA's Kennedy Space Center, something that would likely push back the launch date from September 2025 to 2027 at the earliest. Another alternative would be to do nothing and fly the Artemis II mission as is.
“The whole trading window is open,” Koerner said. “But as far as the actual Artemis II mission, we're still holding on to the September '25 launch date at this point, knowing that we still have a lot of work to do to complete the heat shield study.”
