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NASA still investigating Orion heat shield issues from Artemis 1 moon mission
The landmark 2022 moon mission was a success, but questions remain about how Orion's heat shield performed.
![illustration of a conical space capsule blazing through Earth's atmosphere](https://cdn.mos.cms.futurecdn.net/AUZkT6GeHkt4nipnDGaqwC-320-80.jpg)
Earlier this year, NASA announced it had delayed until September 2025 the crewed Artemis 2 swingby of the moon, a practice run to prepare for 2026's Artemis 3 mission, which will land astronauts near the lunar south pole.
One reason cited for the 10-month delay was getting to the bottom of reentry heat shield data from Artemis 1, which sent an uncrewed Orion capsule to lunar orbit and back.
Engineers have been analyzing data from that shakeout cruise, which began with a launch by NASA's Space Launch System megarocket on Nov. 16, 2022.
The 25-day Artemis 1 mission ended on Dec. 11, 2022, with the Orion capsule splashing down under parachutes in the Pacific Ocean off Baja California.
Related: The 10 greatest images from NASA's Artemis 1 moon mission
Blistering reentry
Orion's heat shield took on the 25,000 mph (40,000 kph) reentry speed that day, protecting the capsule ably. But soon thereafter, NASA and contractors began wrestling with the discovery that Orion's ablative heat shield wore away differently than predicted.
Some areas of expected charred material ablated away in a manner not forecast by computer modeling and ground testing. Also, there was slightly more liberation of the charred material during reentry than anticipated.
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Orion's heat shield features the same ablative material, called Avcoat, used during the Apollo program in the late 1960s and early 1970s. However, the building process for the heat shield was changed from the Apollo-era method.
Vintage Apollo
While Avcoat is vintage Apollo, the production process for Orion's 21st-century thermal protection system was altered.
According to Lockheed Martin, the firm leading Orion's heat shield development process, "instead of having workers fill 300,000 honeycomb cells one by one with ablative material, then heat-cure the material and machine it to the proper shape, the team now manufactures Avcoat blocks — just fewer than 200 — that are pre-machined to fit into their positions and bonded in place on the heat shield's carbon fiber skin," the aerospace firm's website explains.
This process allows Avcoat to be applied in just a quarter of the previous time and saves money as well, according to the company.
Root cause
Post-flight inspection of the Artemis 1 Orion heat shield showed an unanticipated loss of char layer pieces from the spacecraft. NASA has been laser-focused, quite literally, on understanding the root cause of the char loss phenomena, as well as Avcoat cracking.
"We designed and executed a building block ground testing approach using agency and external test facilities," NASA's Orion program office told Space.com.
The initial test series began in the summer of 2023 and wrapped up in a last test series in December 2023. "We expect to establish root cause this spring," the NASA office stated.
Simulation testing
Those Orion heat shield tests involved the Laser Hardened Materials Evaluation Laboratory, a unique facility operated by UES, a BlueHalo company in Dayton, Ohio, and managed by the Air Force Research Laboratory. This lab does thermal simulation testing, equipped with high-power lasers.
Testing was also performed at the Arc Jet Complex at NASA's Ames Research Center in California's Silicon Valley. Arc jet testing is done on thermal protection material with plasma mimicking the intense heat generated during the plunging atmospheric reentry of the Orion capsule.
For its part, Lockheed Martin teamed up with NASA to organize a core team of engineers to investigate and understand the cause of the char loss and what would need to be done to prevent similar occurrences on future flights, said Blaine Brown, Orion Spacecraft Mechanical Systems Director at the company.
"Over the past year, the Lockheed Martin team, alongside with NASA, have been very busy producing test articles and supporting reentry environmental tests in various NASA and industry test chambers," Brown told Space.com.
These tests have produced a wealth of information for the investigation team, Brown said. "Lockheed Martin has also been providing analytical expertise to demonstrate acceptable thermal margins to support flight rationale for the Artemis 2 mission."
Related: NASA's Artemis program: Everything you need to know
Heat shield hiccups
Last year, the Orion program office at NASA's Johnson Space Center in Houston responded to a Space.com request for comment about heat shield hiccups.
"We expect the material to ablate with the 5,000 degrees Fahrenheit [2,760 degrees Celsius] the spacecraft encounters on a reentry through Earth's atmosphere, and to see charring of the material through a chemical reaction, but we didn't expect the small pieces that came off, versus being ablated," the NASA office stated.
There was a healthy margin remaining of virgin Avcoat, and temperature data inside the cabin remained at expected levels, so if crew were on board they would not have been in danger, the program office statement explained.
NASA said a dedicated investigation includes planned testing, detailed analysis, extensive sampling of the heat shield, and review of data from sensors to appraise what the Orion capsule experienced on reentry.
Avcoat changes?
Is it possible that changes in the Avcoat may be needed?
"It's still too early in our testing and analysis to arrive at any potential recommendations or solutions that address additional char liberation," the NASA office responded in its 2023 communiqué.
It is possible that the Artemis 1 heat shield phenomenon may just be intrinsic to this heat shield, the office said at the time.
Furthermore, it might be what NASA would expect in the capsule's return from the moon, "but we'll let the data inform us," the Orion project office said, adding that "our teams want the confidence that we have the best heat shield possible to fly humans going forward."
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![Leonard David](https://cdn.mos.cms.futurecdn.net/PCEVx3ScYcaEDjVR8NLHDS.jpg)
Leonard David is an award-winning space journalist who has been reporting on space activities for more than 50 years. Currently writing as Space.com's Space Insider Columnist among his other projects, Leonard has authored numerous books on space exploration, Mars missions and more, with his latest being "Moon Rush: The New Space Race" published in 2019 by National Geographic. He also wrote "Mars: Our Future on the Red Planet" released in 2016 by National Geographic. Leonard has served as a correspondent for SpaceNews, Scientific American and Aerospace America for the AIAA. He has received many awards, including the first Ordway Award for Sustained Excellence in Spaceflight History in 2015 at the AAS Wernher von Braun Memorial Symposium. You can find out Leonard's latest project at his website and on Twitter.
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Loewe-7 I don't understand why they have to come in so hot (40,000 kph). Why must they enter the atmosphere at this extreme velocity?Reply
Could they not slow down the vehicle before re-entry and thus avoid the extreme heat effects? In fact, if they could sufficiently reduce velocity, they could use parachutes to re-enter the atmosphere, yes? -
billslugg
I don't know anything about the specifics of this case but I can make a guess. If they are coming in real fast, it is because they didn't launch enough fuel to be able to slow down at the right time. Adding fuel makes everything bigger and bigger and vastly more expensive. The faster we can learn to come in, the more we can do with what we have.Loewe-7 said:I don't understand why they have to come in so hot (40,000 kph). Why must they enter the atmosphere at this extreme velocity?
Could they not slow down the vehicle before re-entry and thus avoid the extreme heat effects? In fact, if they could sufficiently reduce velocity, they could use parachutes to re-enter the atmosphere, yes? -
orsobubu
yes, this is an answer from an a.i.:billslugg said:I don't know anything about the specifics of this case but I can make a guess. If they are coming in real fast, it is because they didn't launch enough fuel to be able to slow down at the right time. Adding fuel makes everything bigger and bigger and vastly more expensive. The faster we can learn to come in, the more we can do with what we have.
"The reason spacecraft like Apollo or Orion enter Earth's atmosphere at such high speeds is due to the laws of orbital mechanics.
When a spacecraft is orbiting the Earth, it is essentially in a constant state of freefall, balanced between its velocity and the pull of Earth's gravity. To return to Earth, the spacecraft must slow down enough to drop out of orbit and begin descending towards the surface.
However, slowing down in space is not easy. In the vacuum of space, there is no air resistance to naturally slow the spacecraft. The only way to decelerate is to use thrusters or engines, which requires carrying a lot of heavy fuel. It's much more fuel-efficient to let Earth's atmosphere do most of the work of slowing the spacecraft down.
As the spacecraft enters the denser layers of the atmosphere at high speed (around 17,000 mph for Apollo), the air resistance creates intense friction and heat, up to 5000°F or more. This is why the spacecraft needs a heat shield to protect it and its occupants during re-entry.
Theoretically, a spacecraft could use its engines to slow down before re-entry to reduce the heat. But this would require carrying much more fuel, greatly increasing the spacecraft's size and weight, and making the entire mission more expensive and complex. Using Earth's atmosphere to decelerate is a more practical approach.
So in summary, the high re-entry speeds are a consequence of the spacecraft's orbital velocity, and using the atmosphere to slow down, while very hot, is more efficient than carrying extra fuel to decelerate before re-entry. The heat shields and re-entry profiles are designed to manage these extreme but unavoidable conditions of returning from orbit to Earth's surface." -
billslugg Thank you, yes, it makes sense. The hotter you are able to come in, the less fuel you need to deal with.Reply -
TheCoolBrit This I believe has influenced SpaceX so much, The need to slow down before re-entry.Reply
To that end the Starship V3 is growing in size. Thus allowing a Starship variant to refuel in orbit , that is then able to get to the Moon and back and have enough fuel to slow down to enter LEO where it can either dock with a lander or if the additional weight of a full heatshield is possible, Then it can the use the fact the Steel body that can withstand the re-entry temperatures. -
Torbjorn Larsson It is possible Apollo heat shield Avcoat behaved the same, there is no mentioning of an effect comparison.Reply
While it is quite all right to use large language models to get some insight into a new problem - and importantly, to declare it as here - they are known to hallucinate and they won't give proper references. Think of it as a "popular science" take, but check its contribution.orsobubu said:yes, this is an answer from an a.i.:
"The reason spacecraft like Apollo or Orion enter Earth's atmosphere at such high speeds is due to the laws of orbital mechanics.
Yes, it is a problem of fuel consumption. Earth is so massive that it is barely possible to launch chemically propelled rockets to orbit and even less to escape velocities, since the rocket equation means there is an exponential increase in fuel consumption with achieved speed. An orbital launcher has a few percent net cargo mass, typically in the 3-5 percent range. (This is why it is so expensive to send a kg of cargo to orbit, compared to an Earth destination.) Hence missions tend to use minimal propellant energy free ("Hohmann") orbits.
So the higher the orbit, the higher the return energy:
The atmospheric entry interface velocity upon return from the Moon is approximately 36,500 ft/s (11.1 km/s; 40,100 km/h; 24,900 mph) whereas the more common spacecraft return velocity from low Earth orbit (LEO) is approximately 7.8 km/s (28,000 km/h; 17,000 mph).
https://en.wikipedia.org/wiki/Free-return_trajectory
The Hohmann maneuver often uses the lowest possible amount of impulse (which consumes a proportional amount of delta-v, and hence propellant) to accomplish the transfer, but requires a relatively longer travel time than higher-impulse transfers.
https://en.wikipedia.org/wiki/Hohmann_transfer_orbit
A more detailed analysis: https://www.faa.gov/sites/faa.gov/files/about/office_org/headquarters_offices/avs/III.4.1.7_Returning_from_Space.pdf
No, it is not possible to reentry from a 8 km/s orbital speed with a parachute designed for low atmosphere falls at ~ 0.2 km/s for a human in terminal speed fall (fall with aerodynamic lift steady state). The best you can do is a kind of heatshield protected foam bubble.
MOOSE, originally an acronym for Man Out Of Space Easiest but later changed to the more professional-sounding Manned Orbital Operations Safety Equipment, was a proposed emergency "bail-out" system capable of bringing a single astronaut safely down from Earth orbit to the planet's surface. The design was proposed by General Electric in the early 1960s. The system was quite compact, weighing 200 lb (91 kg) and fitting inside a suitcase-sized container. It consisted of a small twin-nozzle rocket motor sufficient to deorbit the astronaut, a PET film bag 6 ft (1.8 m) long with a flexible 0.25 in (6.4 mm) ablative heat shield on the back, two pressurized canisters to fill it with polyurethane foam, a parachute, radio equipment and a survival kit.
https://en.wikipedia.org/wiki/MOOSE
There are ways to reduce high orbital speeds towards low Earth entry speeds though. Besides using gravity assist braking you can try to double up with aerobraking in the case of Earth (or even Mars).
Gravity assistance can be used to accelerate a spacecraft, that is, to increase or decrease its speed or redirect its path.
https://en.wikipedia.org/wiki/Gravity_assist
Aerobraking is used when a spacecraft requires a low orbit after arriving at a body with an atmosphere, as it requires less fuel than using propulsion to slow down.
https://en.wikipedia.org/wiki/Aerobraking
They are somewhat risky methods, especially the latter as it relies on a complex and dynamic atmospheric pressure*, which is why e.g. SpaceX do not (yet, officially) rely on them for its projected Mars missions:
no spacecraft can yet aerobrake safely on its own
*) Think of how solar emissions heightened Earth stratospheric height and drag so a launch of Starlinks failed to reach orbit. -
Torbjorn Larsson
Starship system design is primarily driven by its eventual interplanetary mission capabilities, not by NASA et al. Moon shenanigans. The Moon lander will be dedicated to travel to Moon to be used as a local non-heat shield ferry there, with Orion and its heatshield as the crew craft taking the astronauts to and from lunar orbit. Yes, it will need to be refueled in Earth orbit to reach lunar orbit, and later refueled in lunar orbit - and have a crew environmental control system - so it shares some deliverables with other manned Starship projects.TheCoolBrit said:To that end the Starship V3 is growing in size. Thus allowing a Starship variant to refuel in orbit , that is then able to get to the Moon and back and have enough fuel to slow down to enter LEO where it can either dock with a lander or if the additional weight of a full heatshield is possible,
The 100 mt Moon cargo capability comes without a heatshield (but with Moon land and reorbit propellant). https://en.wikipedia.org/wiki/Starship_HLS No doubt they will have refrigerators and microwaves for "Moon Cordon bleu development" and astronaut R&R. Think of Earth food chains and restaurants that announce sodas and menus that "will take you to the moon"! -
ChrisA
Yes, in theory, they could enter the atmosphere at low speed. But it takes a lot of energy to slow down. In fact it takes as much energy to reduce speed as it took to gain all that speed. SO they would literally need a huge rocket like the one that sent them to the moon and of course all the fuel too.Loewe-7 said:I don't understand why they have to come in so hot (40,000 kph). Why must they enter the atmosphere at this extreme velocity?
Could they not slow down the vehicle before re-entry and thus avoid the extreme heat effects? In fact, if they could sufficiently reduce velocity, they could use parachutes to re-enter the atmosphere, yes?
As it turns out heat shields are MUCH lighter than big rockets and fuel tanks. The heart sheild converts all that kinetic energy to heat and has no moving parts to fail.
Look at how much harder it is to land on the Moon, they need a decent rocket. It is only possible to land on the moon becuase the gravity is so low. Landing one Earth using a lunar-landing-like rocket would be nearly impossible.
Mars is an intermediate problem. They can use a heat shield but they also need rockets and a parachute. Mars has a thin atmosphere and 38% of Earth's gravity.
Venus was the best, heat shields are very effective in the thick atmosphere. As we saw with Pinoneer Venus it is possible to crash land on Venus with nothing but a heat sheild. The air is so thick that the velocity of freefall is low-enough for a survivable crash.
Heat sheilds are the best and most cost effective why to slow a spacecraft for landing -
DrRaviSharma Hello readers!Reply
I can understand the lethargy from the Orion team as can be seen from lack of innovation in many areas by their just copying items, shapes, technologies and materials largely from Apollo. I worked on Apollo 8-17 and also on planning for Space Shuttle and Space Station as early as 1968-1972.
We improved several new items that have proven much more resilience to extreme environment.
While Skylab except for solar panel damage used some prototypes, Shuttle and Station have more robust systems compared to Apollo.
Columbia and Challenger disasters were largely human errors and some of my suggestions were identical to those implemented for post Columbia post-disaster missions for a decade. In my opinion there was need to be more vigilant and we could have continued after 2013 till SpaceX could be ready.
Anyway that is history.
But just as Shuttle discovered materials for low level ablative losses and a lot is happening now in Space Force arena, we could expect SpaceX and Starship technologies to use better materials than Apollo vintage,
In my opinion not enough priority has been give to reentry materials and into preflight robotic missions to prove newer concepts.
Thanks.
Ravi
(Dr. Ravi Sharma, Ph.D. USA)
NASA Apollo Achievement Award
ISRO Distinguished Service Awards
Former MTS NASA HQ MSEB Apollo
Former Scientific Secretary ISRO HQ
Ontolog Board of Trustees
Particle and Space Physics
Senior Enterprise Architect
SAE Fuel Cell Tech Committee voting member for 20 years.
http://www.linkedin.com/in/drravisharma. -
DrRaviSharma Hello readers!Reply
I can understand the lethargy from the Orion team as can be seen from lack of innovation in many areas by their just copying items, shapes, technologies and materials largely from Apollo. I worked on Apollo 8-17 and also on planning for Space Shuttle and Space Station as early as 1968-1972.
We improved several new items that have proven much more resilience to extreme environment.
While Skylab except for solar panel damage used some prototypes, Shuttle and Station have more robust systems compared to Apollo.
Columbia and Challenger disasters were largely human errors and some of my suggestions were identical to those implemented for post Columbia post-disaster missions for a decade. In my opinion there was need to be more vigilant and we could have continued after 2013 till SpaceX could be ready.
Anyway that is history.
But just as Shuttle discovered materials for low level ablative losses and a lot is happening now in Space Force arena, we could expect SpaceX and Starship technologies to use better materials than Apollo vintage,
In my opinion not enough priority has been give to reentry materials and into preflight robotic missions to prove newer concepts.
Ravi
(Dr. Ravi Sharma, Ph.D. USA)
NASA Apollo Achievement Award
ISRO Distinguished Service Awards
Former MTS NASA HQ MSEB Apollo
Former Scientific Secretary ISRO HQ
Ontolog Board of Trustees
Particle and Space Physics
Senior Enterprise Architect
SAE Fuel Cell Tech Committee voting member for 20 years.
http://www.linkedin.com/in/drravisharma