NASA would like to start stacking the Space Launch System rocket for the Artemis II mission—the first human flight around the Moon since 1972—sometime next month, but the agency's exploration chief says the milestone could be delayed as engineers continue studying 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 heating when the capsule blazes through Earth's atmosphere at the end of the 10-day mission. On the Artemis I test flight in late 2022, NASA sent an Orion spacecraft to the Moon and back without a crew aboard. The only significant blemish on the test flight was a finding that charred chunks of the heat shield unexpectedly stripped away from the capsule during reentry as temperatures increased to nearly 5,000° Fahrenheit (2,760° Celsius).
The spacecraft safely splashed down, and if any astronauts had been aboard, they would have been fine. However, the inspections of the recovered spacecraft showed divots of heat shield material were missing. The heat shield material, called Avcoat, is designed to erode away in a controlled manner during reentry. Instead, fragments fell off the heat shield that left cavities resembling potholes.
“A lot of work to do”
NASA launched internal and independent investigations to look into the heat shield issue. Catherine Koerner, NASA's associate administrator for development of exploration systems, told Ars the inquiry remains open.
"We have not made any formal decisions on the forward path yet because we still are doing analysis," she said. "There are a lot of complications associated with the heat shield, not only with identifying a root cause, but also figuring out a path forward once we identify that root cause."
This is a complicated thermodynamic and aerodynamic problem, with engineers studying the combined effects of heating and air resistance as the Orion spacecraft dives deeper into the atmosphere. Victor Glover, the pilot of the Artemis II mission, told Ars earlier this year that ground testing and analyses can only go so far, and some of the dynamics may not be fully understood without more flight data.
Commander Reid Wiseman, mission specialist Christina Koch, and Canadian astronaut Jeremy Hansen will join Glover on the Artemis II mission. They will fly around the far side of the Moon inside the Orion capsule after lifting off from NASA's Kennedy Space Center in Florida on a Space Launch System (SLS) rocket. Artemis II will pave the way for future landing missions to deliver astronauts to the Moon's south pole.
But it's taking longer than NASA officials would have liked to complete the Orion heat shield investigation. Koerner said she didn't want to estimate how much longer it would take for NASA to come to a decision on what, if anything, to change on the Artemis II mission to reduce the risk to the astronauts.
"The best way to ensure crew safety on any activity, but especially this one in particular, is to make sure that they understand that they're doing this—the focus of this investigation and the forward path—with crew safety in mind, and not with schedule pressure or any other kind of external pressure from stakeholders," she said.
Potential solutions to the heat shield issue for Artemis II include altering the spacecraft's trajectory during reentry or making changes to the heat shield itself. The latter option would require partially disassembling the Orion spacecraft at NASA's Kennedy Space Center, something that would probably delay the launch date from September 2025 until 2027 at the earliest. Another alternative could be to do nothing and fly the Artemis II mission as is.
"The entire trade space is open," Koerner said. "But as far as the actual Artemis II mission, right now, we're still holding to the September ’25 launch date, knowing that we have still a lot of work to do to close out the heat shield investigation.”
Limited life
One decision NASA will soon have to make is whether to begin stacking each of the Space Launch System's twin five-segment solid rocket boosters inside the Vehicle Assembly Building (VAB) at Kennedy. That is supposed to begin next month, with the placement of the bottom segments of each booster on the rocket's mobile launch platform inside the VAB.
But there's a time limit on how long the boosters can be stacked vertically on their launch platform. The joints connecting each piece of the SLS rocket's side boosters were originally certified for one year, but NASA nearly doubled the time limit for the Artemis I launch and could do so again for Artemis II.
Nevertheless, Koerner said NASA wants a better idea of the direction it will go on the Orion heat shield issue before giving the green light to assemble the rocket inside the VAB. "We will wait until we have the decision on the heat shield, or at least understanding of that, before we make the decision on stacking," she told Ars.
The major elements of the SLS rocket and Orion spacecraft are all undergoing preparations at the Florida launch site. The SLS core stage arrived at Kennedy last month, and technicians will mount it between the rocket's twin solid-fueled boosters once those are fully stacked on the launch platform.
Right now, work on the Orion spacecraft is driving the schedule for the Artemis II launch. It's not just the heat shield but also hands-on preparations and testing on Orion inside the Neil Armstrong Operations and Checkout Building at Kennedy. The Orion crew and service modules—made by Lockheed Martin and Airbus, respectively—are bolted together and recently completed tests inside a vacuum chamber to simulate the airless conditions in space.
Ground teams are swapping out batteries and digital motor controllers on the Orion spacecraft to resolve two other technical issues with the vehicle. Once this work is complete, NASA will transfer the spacecraft to a separate facility at Kennedy for fueling and integration with Orion's launch abort system. Then, perhaps in the spring or summer of 2025, Orion will be ready for stacking on top of the SLS rocket.
All that, of course, hinges on NASA deciding Artemis II is safe enough to fly without any hardware changes to the Orion heat shield.
