Moon mission heat shield suffered unexpected wear – 07/03/2023 – Science

The heat shield that protected the Orion capsule on the Artemis 1 mission during its furious re-entry into Earth’s atmosphere on December 11 has suffered excessive and unexpected wear, NASA said Tuesday.

However, program managers do not expect this to delay the next flight — and the first manned trip to the Moon in more than five decades. The American space agency says it is on track to meet the goal of launching Artemis 2 in November of next year.

The thermal shield is basically what protects a spacecraft from burning up like a shooting star in the atmosphere, when crossing it at extraordinary speeds (on a return to the Moon, as was the case with Artemis 1, about 40,000 km/h). The temperature outside the shield can reach something like 2,500°C.

The Orion capsule was successfully rescued from the Atlantic Ocean after a 25.5-day unmanned trip around the Moon and back to Earth, which ended on December 11 last year. The vehicle returned in one piece, as well as the mannequins filled with sensors installed inside, demonstrating the success of the project and paving the way for a manned flight.

However, after retrieving the capsule and analyzing the heat shield, engineers noticed unexpected wear. “The heat shield showed more variations than expected, with more material being released than we expected,” explained Howard Hu, Orion program manager, during a post-flight Artemis program update briefing.

Like the shields of the ancient Apollo capsules, which took humans to the Moon in the last century, Orion’s shield is made of a material called Avcoat, which has ablative properties: it is basically a plastic resin whose function is to be carbonized (converted into gas) by the re-entry heat and thus dissipate it.

The new shields also have the same shape as the old ones, but are slightly larger (to account for the Orion, which has a larger diameter than the old Apollo) and are manufactured differently: instead of a single piece, they are made up of 186 blocks. fitted side by side.

The joints between them, a potential sticking point, worked exactly as expected. However, part of the ablative material, instead of being completely carbonized, ended up crumbling and becoming loose in some of the blocks, contrary to what was expected from the models.

The anomalous behavior, at the moment, is more of a concern because of the lack of understanding of what is happening than because it offers any additional risk. “We have significant headroom on the heat shield, and I don’t think we’ve gone beyond any limits,” Hu said, stressing that the issue will be investigated in detail.

“We’re going to go through each block, take measurements, take data from the re-entry images, correlate with the heat shield sensors, look at our computer models and understand the phenomenon. There’s a lot of work to be done, we just put everything together, and We are now going to move forward with that assessment.”

the good news

Not everything was scary. Incidentally, it is natural to focus on what worries you the most, but program managers never tire of emphasizing the success of the Artemis 1 mission, which fulfilled all the initial objectives of the test flight and others inserted in the middle of the journey, due to the good spacecraft performance. “We were able to meet 21 new targets, performance was better than expected and we were able to push the envelope,” says Hu.

An important sign of progress was that the team responsible for Orion has already managed, ahead of schedule, to remove all the avionics (the electronic system) from the capsule and install it in the next one to fly, this time with a crew, on the Artemis 2 mission.

This recycling foreseen in the program could be one of the knots capable of delaying the next flight, at the moment scheduled for the end of November 2024. Asked if there was a possibility of advancing the schedule, Jim Free, NASA’s deputy administrator responsible for developing the systems of manned exploration (everything that is being designed to take humans beyond Earth orbit), said there is no prospect of bringing the mission forward, “but it helps build headroom into our timeline.”

Preparations for Artemis 2 are ongoing. According to Hu, Orion’s European service module (provided by the European Space Agency and manufactured by Airbus) for the next flight should complete its tests in mid-May, and the command module (responsibility of Lockheed Martin, main contractor of Orion), in mid-June. The two are expected to unite by the end of June.

Meanwhile, the next SLS rocket, which has Boeing as the prime contractor, is also in the process of being assembled at the Michoud Assembly Facility in New Orleans. Two of the four center stage engines have already been unpacked for installation.

On platform 39B at the Kennedy Space Center, work on repairing and updating ground systems for launch is also progressing. The two elevators were damaged during the takeoff of Artemis 1. One of them is already operational, and the second is in the repair phase. Teams are considering installing additional protections to prevent similar damage in future releases.

The crew, the most important item in the Artemis 2 mission, is not scheduled yet. But certainly there is enormous apprehension among astronauts, to know who will be the first humans to go around the Moon in the 21st century, which — for now — is scheduled to happen by the end of next year.