After two years of silence, NASA publicly acknowledged the dubious qualities of the Orion spacecraft’s heat shield. Worst of all, it was decided to leave the heat shield as is, and even in worse condition than that of the first Orion, which flew around the Moon without a crew two years ago. The agency’s leadership was widely criticized for this decision. However, the new NASA leadership will have to sort it all out.
Image source: NASA
The fact that something was wrong with the Orion heat shield became known in May of this year after the publication of photographs of the ship with pieces of the screen falling off. The photographs were published by NASA’s chief inspector after reviewing the agency’s activities. In April, NASA created an independent review team (IRT) to evaluate the problem and draw conclusions. The group submitted its report to the agency in August, but NASA hid it in the back of its desk. And not surprisingly, a campaign to rescue the Boeing Starliner pilots stuck on the ISS was in full swing. No one needed another significant problem.
NASA revealed what was wrong with the heat shield only last Thursday at a press conference. As the commission found out, the heat shield turned out to be poorly permeable to gases. It consists of 186 tiles of Avcoat material manufactured by Textron Systems under license from Lockheed Martin. The tiles are glued to the titanium base of the capsule body. When entering the Earth’s atmosphere at a speed of 40 thousand km/h and after the shield was heated to 2760 °C, gases were released inside the shield. Due to poor permeability of the screen material and the seams between the tiles, the gases created pressure and exploded the screen from the inside. They were expected to burn evenly and reduce thickness.
A capsule without entire pieces of the heat shield risks burning out in this place. However, aerodynamics are also questionable. The air pressure there is such that the capsule can spin. During the descent of the Orion spacecraft during the Artemis 1 mission, the destruction of the heat shield did not lead to a critical increase in temperature inside. But the heat shield on the Artemis 2 mission, which will fly four astronauts for the first time, is even worse.
While working on the Orion heat shield for the unmanned Artemis 1 mission, it turned out that ultrasonic diagnostics of shield integrity did not work well enough. To make it work better, it was proposed to increase the impenetrability of the shield, which was embodied in the screen for Orion of the Artemis 2 mission. As is now clear, this was a wrong decision, which only increased the risk of screen destruction. And now this ship with a screen of questionable reliability is being prepared for installation on the first stage of the SLS rocket for the Artemis 2 mission. NASA management gave the go-ahead for this operation, explaining that they simulated a safer trajectory for Orion’s entry into the Earth’s atmosphere. The trajectory was assessed using Monte Carlo statistical analysis, which shocked the experts in the field.
«“I worked at NASA for 45 years,” said former astronaut and heat shield specialist Charles Camarda. — I love NASA. I don’t like the way NASA has become. I don’t like that we’ve lost our research culture.” In a LinkedIn post, Camarda said the space agency and its leadership team should be “ashamed.” In an interview Friday, he reiterated that NASA is relying on flawed probabilistic risk assessments and Monte Carlo simulations to determine the safety of Orion’s existing heat shield.
«Expediency trumped safety and good materials science and engineering. Sad day for NASA,” Ed Pope, an expert in advanced materials and heat shields, wrote on LinkedIn.
The state of the heat shield of the first Orion spacecraft returning from the Moon
At the same time, the head of the IRT special commission, Paul Hill, a former NASA flight director and an expert on the Columbia shuttle disaster in 2003, claims that agency specialists did not try to hide anything regarding problems with the Orion screen. All data was provided in full, tests were carried out, reports were prepared. At the beginning of the commission’s work, two of its members were against using the screen in its current form, but by the time the conclusion was prepared, everyone unanimously recognized the screen as capable of withstanding flight in the atmosphere when the entry trajectory changes.
Since assembly of the SLS rocket for the Artemis 2 mission has already begun, new NASA management will have to take responsibility for the fate of the mission after the appointment of Donald Trump in January or February 2025. For the Artemis 3 mission with astronauts landing on the Moon, the Orion spacecraft will receive a modified heat shield. In this regard, the crew of the Artemis 2 mission is at greater risk. They will have to fly with what they already have, being aware of the level of risk.