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Apollo and Orion Avcoat

AVCOAT 5026-39 is a NASA code for several versions of a specific ablative heat shield material originally created by Avco for the Apollo program.[1][2][3] It is composed of silica fibers in an epoxy novolac resin. The original AVCOAT was used for the Apollo Command Module heat shield. A reformulated version was used for the initial Orion heat shield and later for a redesigned Orion heat shield.

History

[edit]

AVCOAT was used for the heat shield on NASA's Apollo command module.[4] In its final Apollo form, this material was called AVCOAT 5026–39.

Although AVCOAT was not used for the Space Shuttle orbiters, NASA again used the material for its Orion spacecraft[5] first for the initial Orion test and then for a different type of heat shield for the later Orions. The Avcoat used on the two types of Orion shield was reformulated to meet environmental legislation that was enacted after the end of Apollo.[6][7]

Specifications

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AVCOAT-based heat shields

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Apollo Command Module

[edit]
Ablative heat shield (after use) on Apollo 12 capsule

AVCOAT was first used on the parts of the Apollo spacecraft orbiter and as a unit attached to the crew module. The heat shield is a honeycomb structure filled with the AVCOAT. NASA confirmed that this is made of silica fibers with an epoxy novolac resin filled in a fiberglass-phenolic manufactured directly onto the heat shield.[9][10] The paste-like material was gunned into each of the 330,000 cells of the fiberglass honeycomb individually, a process taking about six months.[11]

NASA's Apollo Flight Test Analysis, AVCOAT 5026-39/HC-G material was tested on the nose cone of a Pacemaker sounding rocket.[12] The temperature and ablation measurements were made at four locations on the nose cap. The report noted that the wear of the shield is due to the aerodynamic shear and heating rate. The report also noted that scientists believed that the ablation was done in a controlled manner.

Orion EFT-1 Crew Module

[edit]
Technicians working on the EFT-1 heat shield
Technician injecting AVCOAT into the heat shield honeycomb

To protect the Crew Module during Earth re-entry, the dish shaped AVCOAT heat shield ablator system was selected. NASA announced that this module would encounter temperature as high as 5,000 degrees Fahrenheit (2760 °C).[13] Licensed by Textron,[14] AVCOAT material is produced at New Orleans's Michoud Assembly Facility by Lockheed Martin. This ablative heat shield was installed at the base of the crew module to provide a controlled erosion moving heat away from the crew module into the atmosphere.

John Kowal, Orion's thermal protections systems manager at Johnson Space Center, discussed the biggest challenge with AVCOAT has been reviving the technology for manufacturing with similar performance as demonstrated in the Apollo Missions.[13] After the Apollo missions, Avcoat variants were produced and studied. Orion Chief Engineer requested the heat shield to be redesigned,[15] however the final design was not selected.

The Orion Crew Module was first designed for the NASA's Constellation program. The heat shield was designed and manufactured similarly to the Apollo version as a monolithic fiberglass honeycomb which was then filled with the AVCOAT. The honey comb consisted of 330,000 small cells. Each cell was individually filled with AVCOAT one at a time by a technician with a pressure gun, with the process taking more than six months for the shield.[16]

The EFT-1 mission performed two orbits of Earth providing the opportunity for Orion's systems to be tested. It took about four hours with the splash down in the ocean.[17] This was the only flight with this heat shield.

Orion Artemis Crew Module

[edit]
ASRC Federal technicians inspect AVCOAT block bonding on the Artemis II heat shield on at Kennedy Space Center on July 2, 2020.
Artemis I heat shield showing spalling after recovery

After the end of the Constellation program, Orion was adapted for use with the Space Launch System to replace the Space Shuttle program. This spacecraft was planned to take astronauts to the International Space Station (ISS) in 2015 and to the moon in 2024. However, Orion was never used for ISS. Its first flight after EFT-1 was the uncrewed Artemis I, which flew in 2022.

Manufacture of the EFT-1 heat shield was labor-intensive and there were concerns that the monolithic honeycomb design was inappropriate for the large Orion shield. Therefore, the shield was redesigned to use carefully shaped Avcoat blocks instead.

The AVCOAT material heat shield went through several rounds of testing before being chosen for the installation. During the investigation of the thermochemical response of Avcoat TPS (based on first principles for comparison with EFT-1 data), things being tested on the heat-shield included: modeling of gas transport, heat transfer, and TPS material regression.[18]

Orion's 16.5 feet AVCOAT heat shield was secured onto the Orion Crew Module using 68 bolts by Technicians at NASA's Kennedy Space Center (KSC) in Florida. This heat shield is covered in titanium truss and a composite substitute with an addition skin made of carbon fiber layers. Orion's heat-shield was designed and manufactured by Lockheed Martin. The heat shield is like pieces of a puzzle that all must fit together perfectly and the bolt fittings must be lined up.[14]

After the heat-shield's installation, access to components of the crew module became difficult or no longer accessible.

Artemis I heat shield performance

[edit]
See also: Artemis I § Post-landing analysis

After the Artemis I Orion capsule was recovered, inspection showed unexpected loss of material from the heat shield. NASA undertook an exhaustive and complex analysis of the loss, and was finally able to report on it and announce recommendations after two years, on December 5, 2024. The conclusion was that the damage was initiated by spalling caused when gas trapped within the shield heated and then expanded when external pressure was reduced, blowing pieces out of the shield. This occurred during the reentry "skip" maneuver, which had a different heating and cooling profile than simpler direct-entry profiles.[19]

Later Artemis missions

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Based on the Artemis I analysis, NASA decided to use the already-installed identical heat shield for the Artemis II mission, but to fly with a different re-entry profile that would not allow the external pressure to be reduced. Since the Artemis III shield was not yet installed, NASA chose to change the AVCOAT formulation for it. This revised formulation will not trap gasses within the shield, and this in turn allows the capsule to use the preferred reentry skip maneuver.[20]

Flight use

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Uncrewed

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Crewed

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See also

[edit]

Phenolic-impregnated carbon ablator

References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

AVCOAT

View on Grokipedia
from Grokipedia
AVCOAT is an ablative thermal protection system (TPS) material designed to shield from extreme during atmospheric re-entry, functioning by charring and eroding to dissipate heat while maintaining structural integrity. It consists of an novolac resin matrix reinforced with silica microballoons, phenolic microballoons, and silica fibers, typically contained within a fiberglass-phenolic for application directly onto the vehicle's substrate. With a low of approximately 529 kg/m³, it offers effective properties, including an effective heat of around 23.8 MJ/kg and moderate thermal conductivity of 0.242 W/m-K at standard conditions. Originally developed by Avco Corporation (now part of Textron Systems) in the early 1960s, AVCOAT—specifically the formulation AVCOAT 5026-39—was rapidly qualified and became the primary heat shield material for NASA's Apollo command module, enabling safe re-entries for all crewed lunar missions from Apollo 7 through Apollo 17. The material's honeycomb-integrated design allowed for precise manufacturing, with the Apollo heat shields produced by filling over 300,000 cells in the honeycomb substrate with the ablative mixture. After a hiatus following the Apollo program, NASA reselected AVCOAT in April 2009 as the baseline TPS for the Orion Multi-Purpose Crew Vehicle's heat shield, adapting the proven Apollo-era formula to modern production techniques like block casting at facilities such as NASA's Michoud Assembly Facility. This choice was driven by its flight heritage, lightweight nature, and ability to withstand peak re-entry temperatures exceeding 2,700°C, though subsequent testing for Artemis missions revealed challenges like unexpected charring patterns, leading to design refinements. In December 2024, NASA identified the cause of char loss observed during the uncrewed Artemis I mission in 2022 as insufficient gas release from the AVCOAT material, resulting in cracking and detachment; enhancements have been implemented for subsequent missions, with the Orion spacecraft for the crewed Artemis II delivered in May 2025 and targeted for launch in April 2026. Over its history, AVCOAT has undergone extensive qualification, including more than 1,000 tests for Orion alone, underscoring its role as a cornerstone of ablative TPS technology in human spaceflight.

Development History

Origins in the Apollo Program

AVCOAT was developed by the Avco Corporation in the early 1960s specifically as AVCOAT 5026-39, an ablative material tailored for protecting the Apollo Command Module during high-speed atmospheric re-entry. Initiated in early 1961, the material evolved rapidly to meet the demanding requirements of lunar return velocities reaching 36,333 ft/sec, which imposed heating environments far more severe than those of prior programs like Mercury and Gemini. The key motivations for its creation centered on the need for a lightweight, high-temperature-resistant ablative system capable of enduring peak stagnation heating rates up to 800 Btu/ft²-sec, corresponding to surface temperatures exceeding 5,000°F (2,760°C), while minimizing overall mass and ensuring structural reliability. To validate its performance, Avco conducted extensive initial testing phases, including ground-based plasma arc jet simulations to replicate re-entry conditions and subscale flight tests such as the series in 1964 and R-4 in 1964, which confirmed the material's controlled and thermal protection characteristics. Following evaluation against competing materials, AVCOAT 5026-39 was selected in April 1962 for the due to its superior char integrity—maintaining under prolonged high-heat exposure—and lower compared to alternatives like Corning DC-325 and ESM-1000, which exhibited inconsistent and higher weight penalties. Production was then scaled up significantly, with each command module requiring the manual filling of approximately 370,000 individual cells with the AVCOAT resin mixture, cured under controlled conditions to form a monolithic ablative layer bonded to the module's substructure.

Revival and Modifications for Orion

Following the conclusion of the Apollo program in the 1970s, production of the original AVCOAT formulation ceased as environmental regulations restricted the use of certain phenolic compounds, prompting a hiatus in its application until the Orion program's revival. In 2007, NASA and Lockheed Martin initiated an extensive evaluation of ablative materials for Orion's heat shield, testing eight candidates over three years to withstand re-entry velocities up to 11 km/s—significantly higher than Apollo's lunar returns. By April 2009, AVCOAT was selected over phenolic impregnated carbon ablator (PICA) due to its mature technology, robust thermal and structural performance, and proven ablation properties from the Apollo era as a baseline. For Orion, AVCOAT underwent reformulation to comply with environmental legislation enacted after Apollo, including U.S. Toxic Substances Control Act (TSCA) and REACH standards, while preserving its core epoxy-novolac and silica fiber composition for effective . A major engineering adaptation shifted from the Apollo-era poured method—manually injected into cells—to pre-impregnated blocks machined from large billets, enabling easier application, reduced seams, and tailored thickness for specific zones. This tile-like block design, comprising about 180 pieces bonded to a carbon composite carrier with adhesives and gap fillers, improved overall uniformity and addressed potential cracking at interfaces observed in preliminary configurations. Manufacturing advancements included automated processes for billet machining and bonding at NASA's , supplemented by non-destructive evaluation techniques such as terahertz imaging, ultrasonics, and scans to verify density and void-free integration. To ensure consistency, engineers tested over 1,000 AVCOAT samples in arc jet facilities, simulating re-entry plasma flows to validate rates and structural integrity under varying heat fluxes. These innovations reduced production time by approximately 75% compared to honeycomb filling and facilitated scalable output for the . AVCOAT achieved qualification for Orion's (EFT-1) by 2014, employing a substrate similar to Apollo for the uncrewed orbital . Post the 2022 Artemis I mission, where lower-than-expected heating rates during skip re-entry revealed insufficient gas permeability in the material—leading to trapped gases, buildup, cracking, and uneven char loss— implemented refinements to enhance and uniformity. Analysis of 200 recovered samples and 121 additional ground s confirmed that targeted permeability improvements, achieved through adjusted processing parameters, would prevent recurrence without altering the overall design. In December 2024, identified gas pressure buildup as the root cause and enhanced arc jet testing facilities to validate the fixes, ensuring crew safety for subsequent flights including II.

Material Composition and Properties

Chemical and Physical Composition

AVCOAT is a low-density ablative material primarily composed of an novolac matrix reinforced with fibrous fillers and microspheres. The system incorporates approximately 25% by weight of fibrous filler, consisting of equal parts chopped silica fibers (nominal length of 0.25 inches or 0.6 cm) and milled E-glass fibers, which provide structural integrity and char strength during ablation. Additionally, the matrix includes about 30% by weight phenolic microballoons, along with silica microballoons, to achieve a lightweight syntactic foam-like structure upon curing with appropriate agents. The material is applied over a glass phenolic honeycomb substrate, forming panels where the ablative mixture is gunned into individual hexagonal cells to ensure uniform distribution and minimize voids. Each honeycomb panel features cells with a of approximately 3/8 inch (0.95 cm), and the Apollo Command Module required filling roughly 330,000 such cells across its surface. The resulting ablative layer exhibits a of 0.51 g/cm³ (32 lb/ft³), contributing to its overall low mass while maintaining mechanical stability. For the Orion Crew Module, AVCOAT underwent minor reformulation to replace restricted solvents and additives, ensuring compliance with modern environmental regulations, though the core silica-resin and filler ratios remained essentially unchanged. This version retains the novolac base with silica fibers and microballoons embedded in the substrate, preserving the material's foundational properties.

Thermal Performance Specifications

AVCOAT operates through an endothermic mechanism, in which the phenolic matrix decomposes under intense , releasing gases and forming a protective char layer composed primarily of silica fibers and carbon residue that insulates the underlying while radiating away from the surface. This char layer acts as a barrier, slowing conduction to the , with the process consuming material to maintain surface temperatures below structural limits. Key thermal performance specifications include the ability to withstand surface temperatures up to 2,760°C (5,000°F) for durations of 10-15 minutes during atmospheric re-entry, as demonstrated in Apollo and Orion testing environments. The material exhibits a thermal conductivity of 0.2-0.5 W/m·K in its virgin state, which decreases further in the charred form due to the porous structure, enhancing insulation. rates under peak conditions range from 0.1-0.5 mm/s, depending on coefficients and environmental factors like and oxygen flux. During re-entry, AVCOAT experiences significant mass loss resulting from gas evolution and surface , with the remaining char providing ongoing protection. Surface is modeled using the approximate for steady-state : δ=qρ⋅ΔH⋅t\delta = \frac{q}{\rho \cdot \Delta H} \cdot t where δ\delta is the recession depth (m), qq is the (W/m²), ρ\rho is the material density (kg/m³), ΔH\Delta H is the heat of ablation (J/kg), and tt is exposure time (s); typical values include ρ≈530\rho \approx 530 kg/m³ and ΔH≈2.38×107\Delta H \approx 2.38 \times 10^7 J/kg. Performance is validated through arc jet simulations replicating re-entry conditions, with fluxes ranging from 1,000-5,000 W/cm² to assess behavior across pressures and oxygen levels. For the Orion program, post-Artemis I (2022) testing revealed unexpected char loss due to plasma flow interactions, prompting refinements in for enhanced uniformity and reduced gas entrapment during , with improved permeability on the order of 10−1210^{-12} m² to better vent gases and minimize internal pressure buildup.

Spacecraft Applications

Apollo Command Module Heat Shield

The Apollo Command Module (CM) heat shield featured a blunt-body conical with a diameter of approximately 3.9 meters, optimized to maximize aerodynamic drag during . This configuration covered the forward section of the CM, utilizing AVCOAT as the primary ablative material applied over a phenolic substrate to form a unified thermal protection layer. The AVCOAT thickness varied from 1.8 cm on the leeward surfaces to 6.9 cm at the , ensuring graduated protection against peak heating loads. Integration of the AVCOAT heat shield involved bonding the filled honeycomb panels to the underlying aluminum skin of the CM using HT-424 adhesive, followed by a curing process at 325°F to achieve secure adhesion across the curved surfaces. The honeycomb featured 3/8-inch (0.95 cm) diameter cells, which were filled with AVCOAT via a gunning technique from the bottom upward to minimize voids and ensure uniform distribution. The complete heat shield assembly weighed approximately 848 kg, accounting for roughly 20% of the CM's total entry mass and necessitating careful mass budgeting to maintain overall spacecraft balance. Engineering choices emphasized reliability and gas management, with the honeycomb cells oriented perpendicular to the shield's surface—effectively radial along the conical —to channel byproducts away from the high-heat stagnation region and reduce aerodynamic interference. This monolithic panel approach, rather than segmented tiles, was selected for its characteristics, allowing the material to char and erode controllably without catastrophic detachment. AVCOAT's low-density composition, incorporating epoxy-novolac with silica microballoons, enabled effective heat dissipation through and sublimation during reentry. To validate performance, the underwent extensive ground testing, including full-scale water drop and impact simulations to assess structural and load distribution on the post-ablation surface during . Complementary tests, conducted on full-scale CM prototypes such as vehicles 004, 008, and 2TV-1 at NASA's , simulated entry heating environments to confirm bonding strength and material response under thermal stress. These evaluations addressed potential vulnerabilities in adhesive joints and honeycomb . The design was specifically tailored for lunar return entry velocities of 11 km/s, incorporating margins to accommodate up to 20% variations in trajectory parameters such as angle or skip trajectories, ensuring crew safety across a range of mission profiles.

Orion Crew Module Heat Shield

The Orion Crew Module incorporates AVCOAT in a 5-meter-diameter truncated configuration, bonded as pre-machined blocks to a carbon composite base structure supported by a skeleton, with the overall heat shield assembly weighing approximately 1,800 kg. These blocks vary in size and are tapered in thickness from 2.5 to 7.6 cm depending on exposure to reentry heating, enabling modular application across the forward-facing surface. Approximately 180 blocks are used, a significant reduction from the honeycomb cells of earlier designs, facilitating faster assembly and easier individual replacement if needed. Key adaptations from the Apollo-era implementation include the shift to a block or tile format for AVCOAT, which contrasts with Apollo's poured, monolithic filling of cells, allowing for improved producibility and reduced manufacturing time by about three-quarters. The backshell of the Orion Crew Module, covering the conical sides, utilizes reusable silica thermal tiles derived from heritage—numbering around 970 to 1,300—rather than a full AVCOAT covering, providing sufficient protection for lower-heat areas while minimizing weight. Embedded sensors within the monitor temperature, pressure, and in real time during reentry, transmitting data to assess performance. The blocks are robotically machined from billets and manually bonded using automated adhesive application and non-destructive evaluation techniques like ultrasonics and X-ray for quality assurance, with integration occurring at NASA's Kennedy Space Center. For the Exploration Flight Test-1 (EFT-1) in 2014, AVCOAT was applied via honeycomb injection using a reformulated version of the original Apollo material to verify suborbital reentry conditions. The Artemis I configuration in 2022 evolved to the block format for enhanced scalability to lunar return profiles, maintaining the same material but with adjusted trajectories to manage heating loads. The Artemis II heat shield uses the same AVCOAT block configuration as Artemis I. To address char loss observed during Artemis I, NASA adjusted the re-entry trajectory to reduce skip dwell time and minimize gas buildup. For Artemis III and subsequent missions, AVCOAT will incorporate enhanced and uniform permeability to prevent cracking and char loss from internal pressure. As of May 2025, delivered the completed Orion crew module for to , incorporating the existing AVCOAT heat shield design. The mission launch was delayed to no earlier than April 2026 to accommodate final verifications. Development involved over ground tests to validate the design under simulated reentry environments, including arc jet facilities like the LENS (Large Energy National Shock) tunnel at , which replicates hypersonic flows up to Mach 20 and temperatures exceeding 2,700°C. These tests confirmed the heat shield's to withstand deeper-space return velocities of up to 11 km/s, building on Apollo's historical precedent for high-speed protection. Additional validation included thermal cycling and mechanical assessments at Kennedy's Operations and Checkout facility to ensure bond and structural .

Mission Deployments

Uncrewed Test Flights

The development of the Apollo underwent rigorous validation through a series of uncrewed suborbital and orbital test flights during the , focusing on its ablative performance under high and reentry conditions without risking crew safety. The series, conducted between 1964 and 1966 at , utilized boilerplate Apollo command modules to simulate launch aborts and maximum ("max ") environments. For instance, the A-002 mission on December 8, 1964, specifically tested the 's capabilities during these high-stress scenarios. Subsequent flights, such as A-004 on January 20, 1966, further evaluated the material's structural integrity and during tumbling abort conditions, confirming its ability to protect the spacecraft structure. Building on these suborbital tests, the and missions provided critical orbital reentry data for AVCOAT. Launched on February 26, 1966, marked the first flight of a Block I , where AVCOAT on the command module heat shields (CM 009) successfully ablated during reentry from an apogee of approximately 305 miles, validating its performance up to orbital speeds. The follow-on mission on August 25, 1966, subjected AVCOAT to higher reentry heating rates, demonstrating consistent ablation and structural integrity without structural failures in the heat shield subsystem. These tests collectively established AVCOAT's baseline reliability for , with post-flight inspections revealing predictable char formation and minimal deviations from ground predictions. Revived for the Orion program, AVCOAT's reformulated version underwent uncrewed testing starting with (EFT-1) on December 5, 2014, a 4-hour, two-orbit mission designed to assess its performance at approximately 80% of lunar reentry speeds (about 9 km/s). The ablated as predicted overall, with post-flight assessments showing excellent thermal protection, though minor excessive recession was noted downstream of compression pads due to flow disturbances. Embedded sensors, including thermocouples at various depths, captured internal temperature profiles confirming the material's integrity, while surface scans and analysis of 182 extracted samples quantified char and zones with no catastrophic failures. This performance, aligning closely with pre-flight models, led to AVCOAT's full certification for subsequent missions. The Artemis I mission, launched on November 16, 2022, represented AVCOAT's most demanding uncrewed test to date: a 25.5-day flight culminating in a skip reentry trajectory peaking at over 5,000°F (2,760°C). While the maintained crew compartment temperatures in the mid-70s°F and protected the vehicle without failure, post-flight inspections revealed unexpected char loss through cracking and spalling in over 100 locations, attributed to gas accumulation in low-permeability AVCOAT regions during the lower heating rates of the skip profile. Thermocouples embedded at multiple depths provided precise data on internal heating and char detachment timing, and of approximately 200 samples showed surface varying by location but with an intact core structure. These anomalies, covering a limited portion of the shield's surface, prompted detailed engineering reviews but did not compromise mission success, informing refinements for future flights.

Crewed Missions

AVCOAT was employed on 11 crewed Apollo missions from 1968 to 1972, spanning through , where it provided thermal protection during atmospheric reentry and splashdown for all flights. These missions included Earth-orbital testing on and lunar operations on the others, with marking the first successful crewed lunar landing and return utilizing the full AVCOAT for a lunar reentry. The material's monolithic design in a honeycomb matrix, with thicknesses ranging from 0.7 to 2.7 inches, ensured consistent performance across varying entry conditions, including inertial velocities of 34,884 to 36,502 ft/sec and entry angles of -6.37° to -6.54°. Performance during these reentries highlighted AVCOAT's reliability, with consistent rates that prevented structural breaches or excessive erosion. For instance, on , the endured surface temperatures approaching 5,000°F for approximately 12 minutes of peak heating while maintaining bondline temperatures below 600°F, demonstrating the material's capacity to dissipate heat loads up to 26,500 Btu/ft²—well within its design limit of 44,500 Btu/ft². Real-time telemetry from embedded sensors in the provided critical data on temperatures, heating rates, and progression, allowing ground teams to monitor the system's integrity throughout the entry phase. Crew safety was further assured by conservative design margins, including up to 50% reserve in depth to account for uncertainties in heating environments. Looking ahead, AVCOAT will feature prominently in the Orion crew module for NASA's Artemis program, with Artemis II slated as the first crewed flight no earlier than February 2026 (as of November 2025)—a 10-day mission involving a lunar flyby for four astronauts. To enhance safety, the mission incorporates a modified, more conservative reentry trajectory with a shallower angle, reducing peak heating on the AVCOAT blocks compared to the steeper profile tested in uncrewed flights. Instrumentation similar to Apollo's will enable real-time from heat shield sensors, ensuring ongoing assessment of and thermal performance during the return from deep space. For Artemis III, targeted for mid-2027 (as of November 2025), the will incorporate enhanced permeability improvements. The Apollo program's use of AVCOAT achieved a 100% success rate in protecting the crew compartment across its 11 crewed reentries, enabling the safe recovery of 24 astronauts and validating the material's efficacy for human-rated missions.

Performance Issues and Improvements

Following the uncrewed Artemis I mission in November 2022, post-flight inspections revealed unexpected char loss on the Orion crew module's AVCOAT , where portions of the charred outer layer detached unevenly, creating cavities resembling potholes. This occurred primarily during the high-heat skip maneuver of reentry, where the spacecraft performed a series of atmospheric skips to manage descent. The root cause was identified as insufficient permeability in the AVCOAT material, leading to trapped gases that built up internal pressure, causing cracking and of the char layer. This non-uniform permeability resulted from variations in the material's manufacturing process, exacerbated by the lower-than-expected heating rates during the skip entry profile. The Independent Review Board, convened in spring 2024 and led by Paul Hill, analyzed the anomaly through extensive testing, including over 100 arc jet simulations, and confirmed that while the char loss affected multiple locations, it posed no to flight or crew survivability, as cabin temperatures remained well within limits. To address these issues, implemented mitigations for subsequent missions without altering the Artemis II heat shield, opting instead for trajectory adjustments to reduce gas buildup by modifying the reentry profile to a hybrid free-return path with fewer skips and lower peak heating durations. For Artemis III, targeted for mid-2027 (as of November 2025), engineers are producing AVCOAT blocks with enhanced permeability through improved mixing and processing techniques at , aiming for more uniform gas release during . These changes build on lessons from Artemis I, emphasizing better control of microcracks to prevent accumulation. The findings have broadened AVCOAT development efforts, prioritizing permeability as a critical parameter for ablative performance in high-speed reentries, with ongoing ground tests validating reliability for lunar return profiles. These enhancements ensure the material's suitability for the program's crewed lunar missions through the late 2020s, while informing potential adaptations for higher-energy entries in future deep-space exploration.

References

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