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Materials Used in Space Shuttle:
Evolution, Challenges, and Future
Prospects
–
an Overview
Irfan Nazir Wani , Kanika Aggarwal , Swati Bishnoi , Pushpendra Shukla , Dineshkumar Harursampath * ,
Ashish Garg *
Posted Date: 22 April 2025
doi: 10.20944/preprints202402.0382.v2
Keywords: space shuttle; materials; thermal protection systems; structural materials; propulsion systems;
re-entry; nanotechnology; composite materials; additive manufacturing; materials science; emerging
materials
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Article
Materials Used in Space Shuttle: Evolution,
Challenges, and Future Prospects—An Overview
Irfan Nazir Wani 1,†, Kanika Aggarwal 2,†, Swati Bishnoi 3, Pushpendra Kumar Shukla 1,
Dineshkumar Harursampath 4,*, Ashish Garg 1,3,5,
1Dept. of Mechanical & Aerospace Engg., Faculty of Engg. and Tech., NIMS Univ., Jaipur, India
2Anisotropic Private Limited, Hyderabad, India
3Department of Chemical Engineering, Indian Institute of Technology Delhi, India
4Aerospace Engineering, Indian Institute of Science, Bangalore, India
5Seminare Private Limited, Delhi, India
*Correspondence: dinesh@aero.iisc.ernet.in (D.H.); ashish@seminare.in (A.G.)
†Denotes the first authors (I.W. and K.A.)
Abstract: The space shuttle, a revolutionary spacecraft that has played a significant role in human
space exploration, was composed of various advanced materials that were carefully selected to meet
the extreme demands of spaceflight. This review paper provides a comprehensive examination of the
materials historically employed in the construction of space shuttles and explores the latest trends shap-
ing the field. The evolution of space shuttle materials is traced from the inception of the space program
to contemporary missions, highlighting key milestones, challenges, and breakthroughs. Emphasis
is placed on the critical role that materials play in the overall performance, safety, and sustainability
of space shuttles. The paper begins by elucidating the diverse requirements that materials must
fulfill in the harsh and complex environment of space, encompassing extreme temperatures, radiation
exposure, and mechanical stresses. A detailed analysis of the materials utilized in the fabrication of
various shuttle components, such as thermal protection systems, structural elements, and propulsion
systems, is presented. Special attention is given to the challenges posed by re-entry and the strate-
gies employed to mitigate heat-related issues. Furthermore, the review explores recent innovations
and emerging materials that are reshaping the landscape of space shuttle design. Advancements
in nanotechnology, composite materials, and additive manufacturing are discussed in the context
of their potential applications for enhancing shuttle performance and reducing mission costs. The
paper also addresses the importance of sustainability in space exploration, exploring materials with
lower environmental impact and improved recyclability. The review concludes with a forward-looking
perspective on the future of materials, considering ongoing research, development, and the potential
incorporation of cutting-edge technologies. Insights are provided into how the evolving landscape
of materials science may influence the design and manufacturing processes of the next generation of
space vehicles. This paper provides an overview of the materials used in the construction of the space
shuttle, including their properties, applications, and challenges. The materials used in the space shuttle
are critical in ensuring the safety, performance, and longevity of the spacecraft, and understanding
their characteristics and performance in space is crucial for the advancement of aerospace engineering.
Keywords: space shuttle; materials; thermal protection systems; structural materials; propulsion
systems; re-entry; nanotechnology; composite materials; additive manufacturing; materials science;
emerging materials
1. Introduction
The Space Transportation System (STS), commonly known as the space shuttle, represented a
groundbreaking achievement in human spaceflight. This reusable spacecraft, developed and operated
by NASA, transformed space exploration by providing a versatile platform for transporting astronauts
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from any ideas, methods, instructions, or products referred to in the content.
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© 2025 by the author(s). Distributed under a Creative Commons CC BY license.
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and payloads to and from orbit. The success of the space shuttle program hinged on the innovative
use of materials that could withstand the harsh conditions of space while meeting stringent safety
and performance requirements. These materials had to endure extreme temperature fluctuations,
vacuum conditions, radiation exposure, and potential impacts from micrometeoroids and space
debris. A key consideration in material selection was weight reduction, as every additional kilogram
significantly increased propellant requirements. This necessitated the use of lightweight yet robust
materials throughout the shuttle’s design. Composite materials played a crucial role in the shuttle’s
construction. Carbon fiber-reinforced polymers (CFRPs), for instance, were extensively utilized in
structural components such as wings, tail, and body panels due to their exceptional strength-to-
weight ratio and resistance to fatigue and corrosion. Various metals were also integral to the shuttle’s
design. Aluminum alloys were employed in the external tank construction, leveraging their low
weight and corrosion resistance. Titanium alloys found application in critical components like landing
gear, owing to their high strength-to-density ratio. Stainless steel was used in certain structural
elements for its durability and heat resistance. Ceramic materials were essential for thermal protection.
Specially designed tiles made from materials such as silica and alumina formed the shuttle’s heat
shield, protecting it from the intense heat generated during atmospheric re-entry. The space shuttle
also incorporated specialized materials for specific functions. Ablative materials were used in high-
temperature areas to absorb and dissipate heat. Radiation shielding materials, including lead and
polyethylene, protected the crew from harmful space radiation. Various insulation materials helped
maintain appropriate temperatures for sensitive components and crew areas. The development and
application of these advanced materials in the space shuttle program not only enabled its success
but also drove significant advancements in materials science and engineering. These innovations
continue to influence modern spacecraft design and have applications in various industries beyond
aerospace. This paper explores the various materials utilized in space shuttle construction, including
composites, metals, ceramics, and other specialized materials. It also examines the challenges, recent
advancements, and emerging opportunities in materials science and engineering for space exploration.
The paper organisation is as follows: The Significance of Materials in Space Shuttle Design is
discussed in section 2. The Historical Overview of Space Shuttle Materials are reviewed and discussed
in Section 3. The Evolution of Materials over Different Shuttle Models and Key Requirements for
Space Shuttle Materials are discussed in Sections 4, and 5, respectively. The Primary Materials Used in
Space Shuttle Construction are discussed in Section 6. Thermal Protection System (TPS) Materials are
discussed in Section 7. Design and Material Requirements for Spacecraft are discussed in Section 8.
Structural materials are discussed in Section 9. Challenges and Future Directions are discussed in
Section 10. Conclusions are discussed in Section 12.
2. Significance of Materials in Space Shuttle Design
The materials used in the space shuttle were required to meet stringent performance standards
and undergo rigorous testing and qualification to ensure safety and reliability. Comprehensive
assessments, including mechanical, thermal, and environmental testing, were conducted to evaluate
their performance under space-like conditions. These tests examined resistance to extreme temperature
variations, vacuum exposure, radiation, micrometeoroid impacts, and space debris encounters, as well
as durability, fatigue resistance, and corrosion resistance. Only materials that met these strict criteria
were approved for integration into the space shuttle, with stringent quality control measures applied
throughout manufacturing and assembly.
Advancements in materials science and engineering have been instrumental in shaping the
materials used in space shuttles. Ongoing research and innovation have led to the development of
advanced materials with superior properties, such as increased strength, reduced weight, improved
thermal stability, and enhanced radiation resistance. The incorporation of cutting-edge composites,
such as carbon nanotube-reinforced materials [
1
,
2
] has shown great potential in achieving exceptional
strength-to-weight ratios, making them highly suitable for future space missions. Additionally,
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nanomaterials, including nanocomposites and nanocoatings [
3
], have been explored for their unique
benefits, such as enhanced toughness, improved thermal and electrical conductivity, and greater
resistance to radiation, water and air penetration [4].
Furthermore, additive manufacturing, commonly known as 3D printing, has emerged as a trans-
formative technology for creating lightweight and complex structures with customizable properties.
This technology has been applied to manufacturing specific space shuttle components, such as small
structural elements and prototypes, with promising prospects for broader implementation in future
space missions. The concept of in-situ resource utilization (ISRU) for 3D printing, where materials
available in space, such as lunar regolith or Martian soil, are used for construction, represents a
groundbreaking advancement that could reduce reliance on Earth-based materials.
In addition to material innovations, advanced modeling and simulation techniques have signifi-
cantly contributed to optimizing materials for space applications. Computational methods, including
finite element analysis and computational materials science, enable researchers to design and refine
materials that meet the demanding conditions of space travel.
The materials used in the space shuttle were fundamental to the program’s success. Carefully
selected and extensively tested composites, metals, ceramics, and other specialized materials met the
critical demands of space travel, including weight reduction, high strength, thermal stability, radiation
resistance, and durability. Advances in materials science, such as novel composites, nanomaterials,
additive manufacturing, and simulation techniques, continue to push the boundaries of space tech-
nology, offering immense potential for the development of next-generation materials for future space
exploration.
3. Historical Overview of Space Shuttle Materials
The emergence of the space shuttle marked a transformative era in space exploration, compelling
the utilization of advanced materials capable of withstanding the rigorous conditions encountered in
space travel. A comprehensive historical overview of space shuttle materials illuminates a progressive
trajectory from the early programs to the sophisticated systems of subsequent models. The inception
of space shuttle materials can be traced to early programs like the Space Shuttle Enterprise, serving as
a prototype for subsequent shuttles. In this formative period, materials confronted the initial challenge
of meeting the demands of an innovative design enabling reusable space travel. Aluminum alloys,
renowned for their lightweight properties, emerged as primary materials in the structural components
of the early shuttles, setting the foundation for the continuous evolution of space shuttle materials [
5
].
As space shuttle technology advanced, corresponding developments unfolded in the materials
employed in their construction. The transition from the prototype phase to operational shuttles,
including Columbia, Challenger, Discovery, Atlantis, and Endeavour, witnessed a refinement in
material selection. A defining feature of this evolution was the introduction of advanced composites,
contributing to heightened strength and reduced weight. The Challenger disaster in 1986 instigated
a thorough reevaluation of materials, driving enhancements in safety and reliability. Subsequent
shuttle models incorporated lessons learned, integrating more robust materials and prioritizing safety
considerations.
The historical evolution of space shuttle materials underscores the escalating emphasis on meeting
stringent performance requirements. The demanding conditions of space travel, encompassing extreme
temperature variations, vacuum exposure, radiation, micrometeoroid impacts, and encounters with
space debris, necessitated materials exhibiting exceptional durability, fatigue resistance, and corrosion
resistance. With each new shuttle model, materials underwent rigorous testing and qualification
processes to ensure their capability to withstand these challenges. The history of space shuttle
materials is intricately linked with advancements in materials science and engineering. Research
and innovation over the years have led to the development of new materials boasting improved
properties, including higher strength, lower weight, better thermal stability, and enhanced radiation
resistance. The integration of advanced composites, exemplified by carbon nanotube-reinforced
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composites, represents a substantial leap forward, offering even higher strength-to-weight ratios and
showcasing the ongoing commitment to pushing the boundaries of materials science in the realm of
space exploration.
4. Evolution of Materials over Different Shuttle Models
The evolution of materials in space shuttle design represents a cornerstone of aerospace engineer-
ing innovation. NASA’s Space Shuttle program, which operated five orbiters—Columbia, Challenger,
Discovery, Atlantis, and Endeavour—over several decades, witnessed significant advancements in
material science aimed at enhancing performance, safety, and efficiency. Space shuttle materials must
withstand extreme conditions, including intense temperature fluctuations, vacuum exposure, radiation
bombardment, and severe mechanical stresses. Extensive research has focused on developing materials
capable of enduring these harsh environments while maintaining structural integrity and operational
effectiveness. This literature review examines the key materials utilized in space shuttle construction,
their properties, and the advancements in materials science and engineering that have enhanced their
development.
Advanced composites, particularly carbon fiber-reinforced materials, have been extensively
utilized due to their exceptional strength-to-weight ratio, thermal stability, and low thermal expansion
coefficients. These materials find applications in body panels, wing structures, and tail assemblies.
High-performance metal alloys play crucial roles in shuttle construction. Aluminum alloys are
used for lightweight structural components, titanium alloys for high-strength elements like landing
gear, and stainless steel for corrosion-resistant parts in propulsion systems. Ceramics offer superior
thermal and chemical resistance, critical for atmospheric re-entry protection. Silica-based tiles, along
with alumina and zirconia composites, form the thermal protection system on the shuttle’s underside.
Specialized materials such as ablative compounds are used in nose cones for controlled heat dissipation.
Thermal barrier coatings are applied to various components for temperature management, while heat-
resistant paints provide additional thermal protection. Ongoing research has led to innovations
such as carbon nanotube-reinforced composites, offering enhanced strength and thermal properties.
Nanocomposites provide improved mechanical and electrical characteristics, while advanced coatings
have been developed for better heat resistance and durability. These advancements continue to push
the boundaries of material performance in space applications, paving the way for future exploration
missions and more efficient spacecraft designs. The integration of new materials and technologies has
not only improved the safety and reliability of space shuttles but has also contributed to advancements
in various industries beyond aerospace.
Metals play a crucial role as fundamental materials in the construction of space shuttles, con-
tributing to the spacecraft’s structural integrity, thermal management, and overall performance in the
demanding conditions of space travel. Aluminum alloys, prized for their lightweight properties, find
extensive use in various structural components, including the fuselage and frame, where strength
and weight considerations are paramount. Titanium alloys, known for their high strength and heat
resistance, are employed in critical structural and thermal components, ensuring durability in the face
of extreme conditions during launch and re-entry. Stainless steel, valued for its corrosion resistance,
is utilized in components subjected to environmental exposure. Inconel and other high-temperature
alloys, with their heat-resistant properties, are specifically chosen for applications in areas experi-
encing extreme thermal conditions.The structural applications of metals extend to the construction
of load-bearing components such as wings, fins, and landing gear, where considerations of stress,
strain, and impact resistance are vital. Moreover, metals contribute to the thermal properties of the
spacecraft, facilitating efficient heat dissipation and playing a role in thermal protection systems (TPS)
that shield the shuttle from the intense heat generated during re-entry. Despite the advantages of
metals, challenges such as thermal stress, fatigue, and corrosion in the space environment necessitate
sophisticated mitigation strategies and coating technologies. Advancements in metal technologies
have seen the development of high-strength alloys and the integration of lightweight metals to enhance
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overall performance. Additionally, additive manufacturing techniques have opened new possibilities
for fabricating intricate metal structures with improved efficiency. As space exploration evolves,
the ongoing exploration of new metal alloys and their integration into next-generation spacecraft
underscores the enduring significance of metals as foundational materials in the continued quest for
space exploration and discovery.
4.1. Aluminum and Titanium Alloys
Columbia, the inaugural space shuttle, featured a predominantly aluminum airframe, comple-
mented by certain structural components crafted from titanium alloys. The lightweight nature of
aluminum was strategically chosen for space travel, while titanium contributed strength to specific
regions [6,7].
4.2. Reinforced Carbon–Carbon (RCC)
The NASA Space Shuttle’s most heat-sensitive areas during re-entry were protected by a specially
engineered Reinforced Carbon-Carbon (RCC) material, which was used in constructing the wing
leading edges and the nose-cap assembly. These components were exposed to extreme temperatures,
requiring a highly resilient thermal protection system. The fabrication of RCC began with a layering
technique where a precursor woven fabric was arranged in alternating 0 and 90-degree orientations,
creating a strong structural foundation. The outer layers underwent a silica infusion process, pene-
trating two to three laminae deep, followed by a high-temperature treatment in an inert atmosphere,
leading to the formation of a silicon-carbide (SiC) coating [8].
This SiC layer was crucial in providing oxidation resistance to the wing leading edges during
the intense heating phase of atmospheric re-entry. However, the extreme processing temperatures
introduced challenges, such as void formation within the carbon-carbon substrate and the development
of micro-cracks in the SiC coating. Despite these issues, RCC’s outstanding heat resistance made
it an essential material for shielding the shuttle’s most vulnerable regions. Its ability to withstand
extreme thermal loads ensured the shuttle’s structural integrity, making it a critical component of the
spacecraft’s thermal protection system [8,9].
The development of RCC marked a major advancement in aerospace materials science, offering
both opportunities and challenges. Its exceptional thermal performance allowed it to maintain struc-
tural integrity under intense heat, while its complex internal structure, resulting from the alternating
ply orientation and multi-step processing, required advanced quality control measures. Managing
voids and micro-cracks necessitated sophisticated inspection and maintenance protocols to ensure the
material’s reliability throughout the shuttle’s missions.
The innovations derived from RCC research continue to shape modern spacecraft design, influ-
encing the development of advanced high-temperature composites. Inspection technologies initially
designed to monitor RCC integrity have found applications across various industries. Additionally,
future spacecraft designed for atmospheric re-entry on Earth and other planetary bodies benefit from
the lessons learned in RCC fabrication and performance, paving the way for next-generation thermal
protection materials.
4.3. Self-Healing Materials for Space Application
Space exploration and interplanetary colonization demand highly durable, reliable, and self-
adaptive materials capable of autonomously repairing damage to spacecraft systems and structures.
Traditional materials used in space applications are susceptible to mechanical wear, thermal stress, UV
degradation, and chemical exposure, which can compromise mission safety and longevity. The devel-
opment of self-healing materials for spacecraft presents a promising solution, enabling the creation of
resilient space structures such as space suits, optical surfaces, liquid-propellant containers, and protec-
tive coatings. These advancements could significantly enhance the feasibility of long-duration space
missions [
10
,
11
]. Furthermore, spacecraft must endure extreme environmental conditions, including
high radiation levels, drastic temperature variations, and the vacuum of space, making the integration
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of self-repairing materials a critical step toward ensuring long-term operational reliability [
12
]. Ex-
trinsic self-healing materials exhibit repeatable self-healing capabilities, but the challenge arises in the
need for energy input to initiate the healing process, particularly in space. Hybrid films incorporating
polymeric nanofillers such as carbides, titania nanomaterials, graphene, derivatives, and MXenes hold
promise in various applications, ranging from EMI shielding and thermal management to self-cleaning
surfaces and fire-resistant materials. Enhancing the performance and feasibility of these materials
requires meticulous fine-tuning, optimization, and a comprehensive understanding of advanced
material processing through effective coordination between level-specific modeling techniques.The
identified areas for innovation present technical challenges that necessitate iterative and explorative
improvements, crucial in their own right. Additionally, a broader outlook for space materials involves
the ambitious goal of integrating multiple functionalities into a single component or material. For
instance, merging self-healing technology with structural health-monitoring composites could enhance
safety, longevity, and feasibility for space applications simultaneously. Similarly, spacecraft featuring
intrinsically EMI shielding/energy-storing composite structural panels would reduce weight and
profile, improving overall feasibility. The combination of self-healing materials with self-cleaning sur-
faces could result in scratch and dust-resistant coatings, enhancing the longevity of solar panels.While
integrating numerous functionalities into a single material poses challenges in maintaining original
functionalities, ongoing advancements in quantum computing and artificial intelligence offer the
potential to overcome these hurdles through advanced materials modeling. Envisioning a satellite
with structural panels serving as antennas and power sources, capable of shape morphing, self-healing,
EMI shielding, self-cleaning, and thermal stability may become a reality with continuous progress in
these fields. Until then, significant research is imperative in the realm of space materials.
4.4. Composites
Composites played a critical role in the construction of the space shuttle, particularly in the fab-
rication of the orbiter. The orbiter, which served as the main vehicle for carrying astronauts and
payloads to and from space, was made primarily of composite materials, including carbon fibres
reinforced polymers (CFRP) and fiberglass composites. These materials offered high strength- to-
weight ratios, excellent thermal stability, and low thermal expansion properties, making them ideal for
aerospace applications. CFRP composites were used in the fabrication of structural components, such
as the wings, fuselage, and tail, due to their high stiffness and strength, while fiberglass composites
were used in non-structural components, such as fairings and access doors.
4.5. Other Materials
In addition to composites, metals, and ceramics, the space shuttle also used various other materials
for different purposes. For example, the windows in the orbiter were made of fused silica, a type
of glass that has high optical clarity and resistance to radiation. The thermal blankets used in the
orbiter’s payload bay were made of flexible insulation materials, such as Mylar and Kapton, to protect
sensitive payloads from extreme temperatures. The adhesives, sealants, and coatings used in the space
shuttle were also carefully selected to meet the stringent require- ments of spaceflight, including low
outgassing, high bond strength, and resistance to vacuum and radiation.
5. Key Requirements for Space Shuttle Materials
The materials used in space shuttles must meet stringent requirements to withstand the harsh
conditions of space travel, re-entry into Earth’s atmosphere, and the stresses of launch and landing.
Here are some key requirements for space shuttle materials:
Thermal Resistance for the Re-entry Heat Protection: Materials must be capable of withstanding
extremely high temperatures experienced during re-entry into Earth’s atmosphere. This is often
achieved through the use of heat-resistant materials such as reinforced carbon–carbon and thermal
protection tiles. Structural Integrity: Space shuttle materials must provide the structural integrity
needed to withstand the dynamic forces and vibrations experienced during launch, orbital operations,
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and landing.
Weight Efficiency: As weight is a critical factor in space travel, materials must be lightweight while
maintaining strength. This requirement helps optimize fuel efficiency and payload capacity.
Aerodynamic Stability: Materials used in the construction of wings and other aerodynamic surfaces
should provide stability and control during re-entry and landing. Protection Against Corrosion: Mate-
rials must resist corrosion due to exposure to the space environment, including the vacuum of space,
radiation, and other corrosive elements [13].
Radiation Shielding: Space shuttles must incorporate materials that provide adequate shielding
against cosmic radiation, which is more prevalent in space than on Earth.
Electromagnetic Interference (EMI) Shielding: mMaterials should be designed to minimize electromag-
netic interference, which can affect the functioning of electronic systems on board.
Thermal Insulation: Effective insulation materials are crucial to regulate internal temperatures, pro-
tecting sensitive equipment from extreme temperature variations [14].
Safety Features: Materials should be fire-resistant to minimize the risk of combustion during launch
and re-entry.
6. Primary Materials Used in Space Shuttle Construction
The extreme conditions encountered by the Space Shuttle during flight necessitated the develop-
ment of specialized materials capable of withstanding severe thermal and mechanical stresses. Some
materials were designed to endure temperatures exceeding 1600°C, while others had to function in
cryogenic conditions as low as -253°C or withstand extreme structural loads. In addition to withstand-
ing these harsh environments, these materials needed to be lightweight to optimize the shuttle’s overall
performance. When configured for launch, the Space Shuttle consisted of three primary components:
the Orbiter, the solid rocket boosters, and the external tank (ET). The shuttle’s thermal protection
system (TPS), which comprised multiple heat shields, was designed with various materials to protect
different parts of the vehicle. The main body of the Shuttle and ET were primarily constructed from
aluminum alloy and graphite epoxy [15].
The TPS incorporated reinforced carbon-carbon (RCC) on the wing leading edges and nose cap to
withstand the highest temperatures. Other critical areas, such as the upper forward fuselage, the entire
underside of the Shuttle, and the maneuvering and reaction control systems, were protected by black
high-temperature reusable surface insulation (HRSI) tiles. Additional sections of the Orbiter were
covered by fibrous refractory composite insulation (FRCI) tiles, which provided improved durability
and strength. Areas exposed to temperatures below 649°C, including the forward fuselage, mid-
fuselage, aft fuselage, vertical tail, and upper wings, were shielded by white low-temperature reusable
surface insulation (LRSI) tiles, advanced flexible reusable surface insulation (AFRSI) blankets, and felt
reusable surface insulation (FRSI) white blankets.
The RCC material was manufactured through pyrolysis of laminated carbon, with its outer surface
converted to silicon carbide (SiC) to prevent oxidation. The FRSI tiles consisted of low-density, high-
purity 99.8% amorphous silica fibers bonded using ceramic processing, resulting in a rigid, lightweight
structure with 90% void space. RCC and HRSI were deployed in areas where temperatures exceeded
1260°C. The FRCI tiles, an advanced high-strength variant, incorporated 20% alumina-borosilicate
fibers and 80% silica fibers, offering enhanced resistance to cracking, improved durability, and weight
reduction compared to HRSI tiles.
The LRSI tiles, composed of 99.8% pure silica fibers, provided thermal protection in regions
experiencing lower heat exposure, while the AFRSI system utilized low-density fibrous silica batting
made from high-purity amorphous silica fibers [
16
–
18
]. The FRSI layer, applied to upper payload
bay doors and fuselage, was composed of glass fibers bonded directly to the Orbiter using room-
temperature vulcanizing (RTV) silicone adhesives.
Additional specialized materials were incorporated into various shuttle components, including
thermal window panes, gap fillers around operable penetrations, and thermal barriers for insulation.
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The external tank’s thermal protection system (ET TPS) utilized sprayed-on foam insulation and
remolded ablator materials, alongside phenolic thermal insulators. Given the extensive range of
materials employed, meticulous attention was required to monitor potential damage caused by debris
impact. Post-flight inspections included detailed assessments of debris found on damaged components,
with subsequent analyses helping to identify sources of damage and prevent future material failures
[19?,20].
The development of materials for structural and engine applications in aerospace has seen signif-
icant progress in recent years. The aerospace industry has greatly benefited from advancements in
alloys based on aluminum, magnesium, titanium, and nickel. Additionally, innovative materials such
as composites are increasingly being integrated into aircraft structures. Despite these advancements,
current aerospace materials still face challenges related to corrosion, stress corrosion cracking, fretting
wear, and mechanical limitations. Extensive research has been conducted to develop the next gener-
ation of aerospace materials that offer improved mechanical performance, corrosion resistance, and
durability. This review covers essential materials used in designing aircraft structures and engines,
along with recent developments in aerospace materials [20,21].
6.1. Smart Materials in Aerospace
In various industries, including aerospace, smart materials—also known as intelligent mate-
rials—are gaining increasing importance due to their unique properties such as self-sensing, self-
adaptability, and memory capability. Despite their potential, a comprehensive review of smart ma-
terials in aerospace has been lacking. Therefore, this study discusses recent advancements in smart
materials and their applications in the aerospace sector. The classification, working principles, and lat-
est developments in nano-smart materials are examined, along with their future potential in aerospace
technologies. Further research in this field is required to explore their full capabilities [22].
6.2. Additive Manufacturing and In-Situ Resource Utilization
Additive manufacturing, commonly known as 3D printing, has emerged as a promising technique
for fabricating complex, lightweight structures with customizable properties. This technology has
been utilized in the production of various components of the space shuttle, including small-scale
structural elements and prototypes. Its adaptability and efficiency make it a strong candidate for
broader implementation in future space missions.
In addition to additive manufacturing, in-situ resource utilization (ISRU) has been proposed as a
means to reduce dependence on Earth-sourced materials. ISRU involves the extraction and processing
of raw materials available in space environments, such as lunar regolith or Martian soil, to manufacture
essential components. This approach has the potential to significantly decrease mission costs and
improve sustainability by enabling on-site fabrication of critical structures.
Furthermore, advancements in computational modeling and simulation techniques have played a
crucial role in optimizing materials for space applications. Tools such as finite element analysis and
computational materials science have allowed engineers to design and refine materials tailored to with-
stand the harsh conditions of space. These technologies have enhanced the ability to predict material
behavior under extreme environments, improving the overall reliability of spacecraft components.
6.3. Aerospace Materials and Military Applications
The design of the Space Shuttle was significantly influenced by military requirements, particu-
larly those of the United States Air Force (USAF), which intended to use the vehicle for launching
reconnaissance satellites and classified missions. Many planned flights were to be conducted from
Vandenberg Air Force Base, where a dedicated launch complex was constructed. However, following
the Challenger disaster, these plans were abandoned, and several missions, including the polar orbit
mission STS-61A, were never executed [23].
Research in aerospace materials for both structural and propulsion applications has progressed
considerably in recent years. The aerospace industry has benefited from the development of advanced
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alloys, including those based on aluminum, magnesium, titanium, and nickel. These materials have
contributed to improved aircraft performance, weight reduction, and enhanced durability. Despite
these advancements, challenges such as corrosion, stress corrosion cracking, fretting wear, and me-
chanical limitations remain prevalent in aerospace materials. As a result, extensive research efforts
have been directed toward developing the next generation of materials that offer superior mechanical
properties and corrosion resistance. This review examines the key materials required for aircraft
structures and engines, along with recent innovations in aerospace materials [21].
In various technological sectors, including aerospace, smart materials—also referred to as intel-
ligent materials—are gaining increasing relevance due to their ability to adapt to external stimuli.
These materials possess unique properties such as self-sensing, self-adaptability, and shape memory,
enabling them to perform multiple functions. Despite their potential, comprehensive assessments of
smart materials in aerospace have been limited. This study aims to address this gap by reviewing
advancements in smart materials and their applicability to aerospace engineering. The classification,
operational mechanisms, and latest developments in nano-smart materials are discussed, along with
their potential applications in future aerospace technologies. Given the limited research conducted
in this area, further investigation is required to fully harness the capabilities of smart materials for
aerospace applications [22].
6.4. Aerogels and Advanced Propulsion Materials
Significant research has been conducted on aerogel materials and their potential use in avia-
tion and aerospace applications. Aerogels, known for their low thermal conductivity, lightweight
structure, and high porosity, offer excellent insulation properties. Their application in aerospace
includes thermal protection for spacecraft, insulation for cryogenic fuel tanks, and shielding against
extreme temperature variations. This study provides a comprehensive overview of aerogel materials,
their properties, recent advances in aerogel production techniques, and potential challenges in their
implementation. The findings serve as a valuable resource for researchers and engineers working on
aerogel applications in aerospace and aviation. In addition to insulation materials, advancements in
propulsion technologies have driven research into novel materials for military aerospace applications.
Future military propulsion systems, including high-speed and hypersonic engines, require materials
that can withstand extreme thermal and mechanical stresses. This review outlines the challenges
and opportunities associated with developing such advanced propulsion materials. It also highlights
key research areas for improving material performance and an overview of ongoing developments
in aeronautical propulsion materials. These insights are particularly beneficial for researchers and
engineers engaged in designing next-generation propulsion systems for military aircraft and spacecraft
[24].
Polymeric materials have been widely used in aerospace due to their lightweight nature, high
strength, and flexibility. However, challenges such as thermal stability, durability, and flammability
must be addressed. Recent developments in aerospace polymers include shape memory polymers,
polymer matrix composites, and nanocomposites, which have enhanced mechanical and thermal
properties. These innovations continue to drive research into advanced polymeric materials for
aerospace applications [25].
Aerogels, known for their low thermal conductivity, lightweight properties, and high porosity,
are also being investigated for aerospace applications. Their potential use as thermal insulation in
spacecraft fuel tanks is particularly promising. Studies have focused on the spray deposition technique
for applying aerogels onto fuel tank surfaces and evaluating their insulation performance. The research
highlights the benefits of using aerogels for improved fuel efficiency and increased safety in space
applications [26].
6.5. Structural Health Monitoring and Composite Materials
The integrity of aerospace materials is crucial for ensuring safety and durability. Structural health
monitoring (SHM) techniques, such as acoustic emission, ultrasonic testing, and fiber-optic sensing,
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are increasingly being used to detect damage in laminated materials. Recent advancements include
the use of machine learning algorithms for data analysis, which enhances the accuracy and reliability
of damage detection [27].
Composite materials, due to their high strength-to-weight ratio, durability, and corrosion resis-
tance, have been widely used in aerospace applications. The development of aerospace composites
has evolved from military aircraft to modern commercial jets and space vehicles. Recent innovations
include the incorporation of nanomaterials and bio-composites, which improve material performance
and sustainability [28].
Thermal protection materials play a critical role in shielding spacecraft from extreme temperatures.
The Space Shuttle’s external insulation system relied on ceramic insulation tiles, which were designed
to withstand high temperatures, low thermal conductivity, and the harsh space environment. The
development process involved material selection, manufacturing techniques, and rigorous testing to
ensure durability. Advances in high-temperature insulation materials, such as silica aerogels, continue
to be explored for future space missions [29].
Multi-layer insulation (MLI) has been developed to provide effective thermal protection while
maintaining a low mass, making it ideal for aerospace applications. Cryogenic insulation techniques are
also being optimized to improve fuel tank insulation, ensuring reliability under extreme temperature
and pressure conditions. Research continues to enhance these insulation materials for next-generation
spacecraft [
30
,
31
]. The aerospace industry continues to evolve with advancements in materials, manu-
facturing techniques, and monitoring technologies. Research into next-generation aerospace materials,
including advanced composites, smart materials, aerogels, and high-temperature ceramics, is essential
for improving safety, efficiency, and sustainability in future space missions. Additionally, innovations
in structural health monitoring and computational modeling will further enhance the design and
reliability of aerospace structures. Continued collaboration between researchers and engineers will be
crucial in overcoming the challenges associated with extreme environmental conditions in aerospace
applications [24,32].
6.6. Development of Ceramic Insulation for the Space Shuttle
The advancement of ceramic insulation systems played a crucial role in enhancing the Space
Shuttle’s thermal protection. The development process involved overcoming key challenges such as
ensuring high-temperature resistance, minimizing thermal conductivity, and maintaining durability
in the extreme conditions of space. Research on ceramic insulation explored material selection,
manufacturing techniques, and rigorous testing methodologies to validate its effectiveness in meeting
the shuttle’s operational requirements. These studies have served as an essential historical reference
for understanding the evolution of external insulation systems in space applications [33].
Finite element analysis was employed to examine the thermal performance of aerogel-based
insulation tiles under different conditions. The study provided valuable insights into heat transfer
mechanisms and the material’s behavior when exposed to high temperatures. The research concluded
that silica aerogel, due to its low thermal conductivity and excellent high-temperature resistance, is a
strong candidate for next-generation insulation tiles. The findings contribute to ongoing advancements
in aerospace insulation materials, aiding engineers and researchers in developing improved thermal
protection solutions for future space missions [29].
Materials originally developed for space exploration have demonstrated potential applications in
other fields, such as medicine. A NASA-led study investigated the feasibility of using Space Shuttle
insulation materials as implants for orthopedic applications. Experimental results indicated that
these materials possess desirable biocompatibility and mechanical properties, making them promising
candidates for medical implants. This study highlights how technological advancements in aerospace
engineering can be adapted for critical applications in healthcare. It also underscores the importance
of interdisciplinary collaboration in fostering innovation [34].
The development of multi-layer insulation (MLI) addressed the challenge of creating lightweight
and reusable thermal protection materials. MLI consists of multiple thin layers of lightweight materials,
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designed to form an insulating blanket that provides high thermal efficiency. Studies demonstrated
that MLI effectively reduces thermal loads, making it an optimal choice for spacecraft insulation. This
research has contributed to the continued evolution of insulation technologies for space applications,
emphasizing the significance of innovative materials in aerospace engineering [30].
Insulating the Space Shuttle’s liquid hydrogen and oxygen tanks posed a significant challenge
due to the extreme temperatures and pressures encountered in space. Research on cryogenic insula-
tion materials aimed to develop solutions that balance weight efficiency and thermal performance.
Advances in this area have highlighted the critical role of insulation technologies in maintaining the
integrity of cryogenic propellant storage, ultimately enhancing mission reliability [31].
The external thermal protection system (TPS) is vital in safeguarding the Space Shuttle from
extreme temperatures and aerodynamic forces experienced during atmospheric re-entry. Researchers
developed lightweight and reusable insulation materials based on ceramic-fiber-reinforced phenolic
composites. Testing and validation of these materials included high-temperature endurance and
impact resistance evaluations. The results demonstrated that these TPS materials offered superior
durability and cost-effectiveness compared to earlier designs, reinforcing their significance in aerospace
applications [35].
The manufacturing of high-temperature reusable surface insulation (HRSI) for the Space Shuttle’s
TPS presented several challenges. The production of LI-900 insulation material required precision
in mixing, extrusion, and curing stages. Variations in environmental factors such as temperature
and humidity affected the final properties of the insulation. Stringent quality control measures,
including extensive testing and inspection, were implemented to ensure consistency and performance.
Research on these challenges has provided valuable insights into the complexities of manufacturing
high-performance aerospace insulation materials [36].
Various mechanical attachment systems were evaluated for securing TPS tiles, including the
"Z-pin" and "Vespel pin" methods. Comparative studies determined that the "Z-pin" method was the
most suitable due to its high attachment strength and ease of tile removal during maintenance. This
research has contributed to optimizing TPS attachment techniques, enhancing the maintainability and
longevity of spacecraft insulation systems [37].
The Space Shuttle’s external fuel tank utilized rigid polyurethane foam insulation. Experiments
using single edge notch bend (SENB) specimens were conducted to assess the fracture toughness of
the foam material. Findings indicated that as foam density increased, fracture toughness decreased.
Understanding the mechanical behavior of foam insulation was essential in ensuring the safety and
structural integrity of the shuttle during flight [38].
Mathematical models were developed to predict the thermal behavior of insulation materials
under varying operating conditions. Experimental data on thermal conductivity, heat capacity, and
thermal expansion were used to refine these models. The results provided a foundation for designing
more effective insulation systems for spacecraft, ensuring optimal thermal performance throughout
the mission [39].
High-speed imaging and laser displacement sensors were utilized to analyze insulation material
erosion during rocket motor firings. The study revealed that turbulent and separated flow regions
exhibited higher erosion rates, emphasizing the need for robust insulation designs. These findings have
been instrumental in improving the durability of insulation materials for space propulsion systems,
ensuring their resilience in extreme environments [40].
7. Thermal Protection System (TPS) Materials
The orbiter’s primary defense against the extreme heat encountered during re-entry is its Thermal
Protection System (TPS). During atmospheric re-entry, the spacecraft experiences intense aerodynamic
heating and air resistance, necessitating highly durable materials to ensure structural integrity. While
each mission results in the loss of some TPS tiles, as long as they do not detach from a concentrated
area, the orbiter remains protected.
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Composed of advanced ceramic materials, these tiles are engineered to endure temperatures
approaching 3,000°F. With over 27,000 individual tiles covering the shuttle, each plays a vital role in
maintaining the spacecraft’s integrity and ensuring a safe return to Earth. The TPS is strategically
designed with different materials applied across various sections of the orbiter to withstand the
broad range of thermal conditions encountered during flight. Positioned as the final layer before the
aluminum and graphite epoxy shell, TPS materials serve as the primary shield against extreme heat.
Operating across a temperature range from -250°F in the cold vacuum of space to nearly 3,000°F
during re-entry, the TPS materials demonstrate remarkable resilience. These materials not only provide
thermal protection but also contribute to the spacecraft’s aerodynamic shape, influencing its descent
trajectory and stability. The selection of TPS materials prioritizes heat resistance, stability under high
temperatures, and minimal weight to ensure effective shielding without compromising the spacecraft’s
efficiency.
7.1. Overview of TPS
The space shuttle is subjected to extreme conditions, ranging from the vacuum of space to high-
temperature environments during re-entry. To maintain safety and functionality, the shuttle relies
on insulation systems designed to regulate heat transfer and protect critical components. One of the
primary aspects of spacecraft insulation is the TPS, which consists of high-temperature ceramic tiles
and reinforced carbon-carbon (RCC) materials capable of withstanding up to 3,000°F. The ceramic tiles
protect regions such as the underside and fuselage, while RCC is applied to the nose cap and wing
leading edges due to their exposure to the most extreme temperatures.
7.1.1. Insulation Blankets
Insulation blankets are used throughout the shuttle to minimize heat transfer between spacecraft
components. These blankets, including multi-layer insulation (MLI), consist of multiple reflective
foil layers separated by low-conductivity spacers. The reflective foil redirects heat away from the
spacecraft, while the spacers reduce conductive heat transfer. MLI blankets are strategically positioned
in key areas, such as the payload bay and external tanks, to prevent heat buildup and maintain thermal
balance in space.
7.1.2. Cryogenic Insulation
Cryogenic insulation is essential for maintaining the low temperatures required for storing liquid
hydrogen and liquid oxygen fuels. The shuttle employs various cryogenic insulation techniques,
including foam insulation, vacuum-jacketed lines, and cryogenic blankets, to prevent heat transfer to
the propellant tanks. Effective cryogenic insulation ensures that these fuels remain in their liquid state,
which is critical for propulsion efficiency and overall mission success.
7.1.3. Structural Insulation
Structural insulation is used in areas exposed to extreme heat, particularly near rocket nozzles
and engines. Materials such as phenolic-impregnated carbon ablator (PICA) and avocet are designed
to char and ablate under high heat conditions, forming a protective barrier that prevents thermal
penetration. This insulation protects the spacecraft’s internal structure from damage and maintains
operational integrity throughout re-entry.
7.1.4. Active Thermal Control Systems
To maintain optimal temperature conditions, the space shuttle employs active thermal control
systems that regulate heat exchange using heaters, coolers, and heat exchangers. These systems are
essential for preserving the functionality of avionics, payload equipment, and life support systems. By
actively controlling the spacecraft’s temperature, these systems ensure that all onboard components
operate within safe thermal limits.
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7.2. Materials for Temperature Regulation
Passive heat management techniques, including surface modifications, coatings, and multi-layer
insulation blankets, play a key role in spacecraft thermal regulation. Metals used in space applica-
tions often require surface treatments to prevent corrosion before launch. Traditionally, hexavalent
chromate-based chemical conversion coatings have been widely used, but due to environmental con-
cerns, alternative coatings such as trivalent chromium and chromium-free options are being explored.
Ongoing research is evaluating these coatings’ effectiveness in preventing corrosion and withstanding
space conditions.
Chemical conversion coatings that comply with MIL-C-5541 standards provide adequate corrosion
protection. However, due to their relatively low thermal emissivity, they may not always meet
spacecraft temperature management requirements. Spacecraft engaged in extravehicular activities
(EVAs) must maintain surface temperatures within safe limits, typically between -118°F and +113°F, to
ensure astronaut safety.
Anodizing processes conforming to MIL-A-8625 standards offer improved thermal regulation
through modifications in absorptance and emittance properties. This specification includes three types
of anodizing: Type I chromic acid (now largely phased out due to reduced chromate use), Type II
sulfuric acid (commonly sealed with hot water for space durability), and Type III hard anodizing (used
for enhanced wear resistance with a thicker oxide layer). However, careful consideration is needed for
hard anodizing in components prone to fatigue.
In cases where additional thermal properties are required, phosphoric acid anodizing and
boric/sulfuric acid anodizing have been tested and found suitable for space applications. These
techniques help optimize the thermal characteristics of spacecraft materials while ensuring corrosion
resistance.
Passive heat control coatings are employed when a lower absorptance-to-emittance ratio is
needed. These coatings, which frequently incorporate binders such as silicone, epoxy, polyurethane, or
potassium silicate, are designed to withstand the harsh conditions of space. Acrylic-based paints are
generally unsuitable for space applications due to their poor performance in extreme environments.
In low Earth orbit (LEO), coatings must resist atomic oxygen erosion, which limits the lifespan
of polyurethane and epoxy coatings. Silicone coatings, particularly low-outgassing variants, are
often preferred for their durability, but caution is necessary when using them near delicate optical
instruments. Potassium silicate coatings are resistant to contamination and highly durable in space,
though their application process can be challenging. Ensuring proper curing times before space
exposure is crucial, as premature exposure can cause cracking and delamination [41].
The accumulation of surface charge on anodized coatings and passive thermal control materials
can lead to operational issues in the space environment. NASA RP-1390 documents instances where
spacecraft failures resulted from electrostatic charging. To mitigate this risk, materials with static-
dissipative properties or conductive coatings are recommended. Indium tin oxide-coated films have
been used for this purpose, though care must be taken to prevent cracking. Additionally, conductive
threads integrated into fiberglass cloth have been explored as an alternative means of reducing surface
charge accumulation.
Overall, advancements in TPS materials and spacecraft thermal regulation continue to evolve,
driven by ongoing research and engineering innovations. The selection of appropriate materials and
insulation strategies remains critical for ensuring the safety and performance of space vehicles during
all mission phases.
7.3. Examples of TPS Materials
Materials for heat regulation and protection have varied functions. Thermal protection materials
are made to endure high temperatures, especially during engine exhaust or re-entry, which can reach up
to 2,800 C (5,070 F). Thermal control materials are used to control temperatures in space conditions. The
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materials incorporated in the TPS are chosen for their ability to withstand the demanding conditions
encountered during space missions and are as follows:
7.3.1. Reinforced Carbon-Carbon (RCC)
Reinforced carbon-carbon (RCC) finds application on critical regions of the orbiter, including
the wing leading edges, the nose cap (encompassing a section on the lower surface), and the vicinity
around the forward orbiter/external tank structural attachment. This specialized material acts as a
thermal barrier, shielding these areas from temperatures surpassing 2,300 degrees Fahrenheit during
re-entry. The production of reinforced carbon-carbon (RCC) tiles involves a multi-step process aimed
at achieving optimal carbon-carbon properties. Initially, a graphitized rayon cloth is impregnated with
phenolic resin, resembling the infusion of juice into the fabric. Subsequently, the impregnated cloth
undergoes curing in an autoclave. After this initial cure, the cloth is pyrolized to convert the resin
into carbon. The cycle is repeated three times, each involving impregnation with furfural alcohol in a
vacuum chamber, curing, and pyrolysis to transform the alcohol into carbon.
To prevent oxidation, the outer surface of the carbon-carbon material is coated with silicon carbide.
The RCC is then packed in a retort alongside a dry pack material composed of alumina, silicon, and
silicon carbide. This assembly undergoes a high-temperature treatment in a furnace within an argon
environment, utilizing a stepped-time-temperature cycle up to 3,200 degrees Fahrenheit. A diffusion
reaction occurs between the dry pack and carbon-carbon, leading to the conversion of outer layers to
silicon carbide, imparting a whitish-gray color. This silicon carbide coating acts as a protective barrier,
shielding the carbon-carbon surface from oxidation. Despite its effectiveness, the silicon carbide
coating is prone to surface cracks due to thermal expansion mismatch. To address this, the RCC part is
impregnated with tetraethyl orthosilicate, providing uniform thermal expansion. The treated part is
sealed with a glossy overcoat for added protection.
The resulting RCC laminate is preferred over a sandwich design due to its lightweight and robust
characteristics. Operating within a range of minus 250 degrees Fahrenheit to about 3,000 degrees
Fahrenheit, the RCC tile aligns with the extreme temperature variations encountered by the orbiter in
space and during re-entry. Additionally, the RCC tile exhibits resistance to fatigue loading experienced
during both ascent and re-entry phases. This comprehensive process ensures the reliability and
durability of the RCC tiles in the demanding conditions of space travel.
7.3.2. Black High-Temperature Reusable Surface Insulation (HRSI)
Black High-Temperature Reusable Surface Insulation (HRSI) tiles, The orbiter is clad in HRSI)
tiles totaling nearly 20,000 in quantity. While not exposed to the highest temperatures, these tiles
play a vital role in withstanding significant heat. Positioned across the orbiter’s surface, HRSI tiles
safeguard regions where temperatures remain below 2,300 degrees Fahrenheit. The High-Temperature
Reusable Surface Insulation (HRSI) tiles are composed of low-density, high-purity silica, specifically
a 99.8-percent amorphous fiber derived from common sand, with fibers measuring between .001 to
.002 inches in thickness. With 90 percent of the tile comprising air and the remaining 10 percent being
material, each tile weighs approximately 9 pounds per cubic foot. The manufacturing process involves
casting a slurry containing fibers mixed with water to create soft, porous bricks, to which a colloidal
silica binder solution is added. After sintering, the resulting block is ready to be cut and machined into
the specified dimensions.
HRSI tiles exhibit varying thicknesses, ranging from 1 to 5 inches, with each tile’s thickness
determined by the level of heat encountered during re-entry. Generally, the tiles become thinner as one
progresses from the front to the back of the orbiter. Enduring cold soak conditions, repeated heating
and cooling, as well as thermal shock during orbit, these tiles must withstand significant temperature
fluctuations without breaking or cracking [42,43].
For instance, an HRSI tile, removed from a 2,300-degree Fahrenheit oven, can be immersed in cold
water without sustaining damage. The surface heat dissipates rapidly, allowing an uncoated tile to be
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held by its edges with an ungloved hand seconds after removal from the oven, while its interior still
glows red. Figure 4 of the reference [?] illustrates the conditions these tiles encounter during re-entry.
The High-Temperature Reusable Surface Insulation (HRSI) tiles undergo a coating process where
the top and sides are sprayed with a glassy material utilizing a liquid carrier. This glass coating is
applied to a thickness of .016 to .018 inches on the tiles, and once coated, they undergo baking in an
oven at approximately 2,300 degrees Fahrenheit. The resulting brick is transformed into a glossy black
finish, rendering it completely waterproof.
Given the minimal thermal expansion and contraction of the tiles (in comparison to the orbiter
structure), it is imperative to incorporate gaps measuring .025 to .065 mils between them to prevent
contact. These gaps are filled with Nomex , referred to as filler bars, ensuring the tiles do not touch
each other.
The HRSI tiles are engineered in two different densities: the first, weighing 22 pounds per cubic
foot, is utilized in specific areas including around the nose, main landing gears, and the wing leading
edge. The remaining areas employ tiles with a density of 9 pounds per cubic.
7.3.3. Fibrous Refractory Composite Insulation (FRCI)
Fibrous Refractory Composite Insulation (FRCI) tiles in black replace some HRSI tiles in specific
high-heat zones. Almost 3,000 FRCI tiles are strategically placed, predominantly at the shuttle’s base,
where the most intense heat is encountered during re-entry. The FRCI tiles, developed by NASA’s
Ames Research Center and manufactured by Lockheed Missiles and Space Division in Sunnyvale,
Calif., represent an advancement of the High-Temperature Reusable Surface Insulation (HRSI) tile
concept. These tiles integrate AB312 (alumina-borosilicate fiber), known as Nextel, into the pure silica
tile slurry. Nextel serves to activate boron fusion, welding the pure silica fibers into a robust structure
during the sintering process. Comprising 20% Nextel and 80% silica, FRCI tiles exhibit distinct physical
properties compared to the original 99.8% silica HRSI tiles.
Following the curing process and the application of a black glass coating, the FRCI tiles undergo
compression during curing to minimize the risk of cracking during handling and operational use.
Beyond the enhanced coating, FRCI tiles boast a lighter weight than basic HRSI tiles. Moreover, they
exhibit a tensile strength at least three times greater than that of HRSI tiles and can endure temperatures
nearly 100 degrees Fahrenheit higher than HRSI tiles.
The manufacturing process for FRCI tiles closely parallels that of the 99.8% pure silica HRSI tiles,
albeit with a higher sintering temperature and some minor adjustments. Once dried, a rigid block is
formed, and the FRCI tiles undergo the same cutting and machining processes as HRSI tiles, exhibiting
variations in thickness. Functionally replacing the HRSI 22 lbs per cubic foot tiles, FRCI tiles possess
a density of 12 pounds per cubic foot. They offer superior strength, durability, resistance to coating
cracking, and contribute to weight reduction in comparison to their HRSI counterparts.
7.3.4. Low-Temperature Reusable Surface Insulation (LRSI)
Low-Temperature Reusable Surface Insulation (LRSI) white tiles serve selected areas like the
vertical tail and upper wing, protecting regions where temperatures are below 1,200 degrees Fahrenheit.
The white color optimizes thermal characteristics, particularly during orbit when the shuttle faces
extremely low temperatures, often dipping below 0 degrees Fahrenheit. The Low-Temperature
Reusable Surface Insulation (LRSI) tiles share the same fundamental construction and perform the
same essential functions as the 99.8% pure silica High-Temperature Reusable Surface Insulation (HRSI)
tiles, but with a reduced thickness ranging from 0.2 to 1.4 inches. The tile thickness is contingent upon
the amount of heat it is expected to encounter during its operational use. Manufactured using the
same process as the 99.8% pure silica HRSI tiles, LRSI tiles are configured as 8x8 inch squares and
are coated to achieve optical and water resistance, with the coating measuring approximately .010
inches in thickness. This protective coating comprises silica compounds infused with shiny aluminum
oxide, enhancing and optimizing optical properties. The installation of LRSI tiles onto the orbiter
mirrors the process used for HRSI tiles. Due to the elevated temperatures experienced during re-entry,
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especially on the wing leading edges, the LRSI tiles have recently been replaced with FRCI and HRSI
tiles. Discovery and Atlantis were the initial orbiters to undergo this replacement.
7.3.5. Advanced Flexible Reusable Surface Insulation (AFRSI)
Advanced Flexible Reusable Surface Insulation (AFRSI) blankets emerged post the construction
of orbiter Columbia. These blankets, comprising sewn composite quilted fabric insulation sandwiched
between layers of white fabric, replace the majority of LRSI tiles on Discovery and Atlantis. With
approximately 1,900 square feet per orbiter, AFRSI blankets offer increased durability, reduced fabri-
cation and installation time, lower costs, and a weight advantage. They are applied in areas where
temperatures do not exceed 1,200 degrees Fahrenheit. The remaining sections of the shuttle that once
utilized Low-Temperature Reusable Surface Insulation (LRSI) tiles have transitioned to Advanced
Flexible Reusable Surface Insulation (AFRSI) blankets. AFRSI consists of low-density fibrous silica
batting, composed of high purity silica and 99.8% amorphous silica fibers [
16
,
17
] with thicknesses
ranging from .001 to .002 mils. This batting is compressed between a woven high-temperature silica
fabric and a low-temperature glass fabric, and the compressed batting is sewn together with silica
thread, creating a quilt-like appearance. The composite density of AFRSI is approximately 8 to 9
lbs per cubic foot, with variations in thickness from 0.45 to 0.95 inches, contingent upon the specific
application and anticipated heat exposure. The utilization of AFRSI blankets not only reduces the
weight of the shuttle but also lowers fabrication and installation costs, along with reducing installation
time. There is a prospect that the entire shuttle may eventually be enveloped in AFRSI blankets,
leading to a substantial reduction in weight. However, before this transition occurs, the AFRSI blankets
must demonstrate their capability to withstand extreme temperatures.
White blankets crafted from coated Nomex Felt Reusable Surface Insulation are utilized on the
upper payload bay doors and sections of the upper wing surface. These blankets serve in areas where
temperatures do not exceed 700 degrees Fahrenheit, providing effective thermal protection for these
specific regions of the orbiter.
7.3.6. Heatshields
Heatshields are frequently used to provide thermal protection and can be created from both
reusable materials, such as ceramic tiles or composites formed of ceramic ma- trix, and one-time use
materials, such as ablatives. The peak heat flux and stagnation pressure experienced during re-entry,
as well as factors like mechanical strength, density, entry angle, and the shape of the heatshield (such
as blunt-body, sphere-cone, biconical, or non-axisymmetric), all play a role in the choice of heatshield
materials. These elements are essential in choosing the best material to offer efficient thermal protection
during high-temperature occurrences. Weight and performance uncertainty must be traded off when
choosing a heatshield’s thickness.
The Flexible Reusable Surface Insulation (FRSI) exhibits varying thicknesses, ranging from 0.160
to 0.40 inches, contingent upon the heat levels experienced during re-entry. These FRSI pieces are
typically 3 to 4 foot squares, with exceptions made for custom cutting when required. Directly adhered
to the orbiter using silicon adhesive, applied at a thickness of approximately 0.20 inches, FRSI is
additionally coated with a white silicon elastomer for waterproofing, as well as to fulfill necessary
thermal and optical requirements. Covering nearly 50 percent of the orbiter’s upper surfaces, FRSI
serves as a crucial protective layer.
A thermal blanket undergoes testing at a temperature nearing 2000 degrees Fahrenheit. While
most of the blankets do not encounter temperatures of this magnitude, the resilience demonstrated in
testing provides assurance, especially considering the potential reassurance it offers to astronauts.
7.3.7. Gap Fillers
Gap fillers are used in areas to restrict the flow of hot gas into the gaps of TPS components. The
types and applications of the various types of gap fillers are shown in Figure 14 (Tile-To-Tile Gap
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Fillers) of the reference [
44
]. The predominant gap filler types that are used are the pillow or pad type
and the Ames type.
Gap fillers made of pillow fabric are typically used to completely fill designated gaps. The
fabrication process for the basic pillow gap filler begins by creating a template that outlines the contour,
height, and width requirements, along with specific thickness details recorded on Mylar. A 0.001-inch
thick sheet of Inconel 601 alloy is then cut to match the gap shape. Aluminoborosilicate fiber (Nextel)
fabric is folded over the Inconel, and the fabric is filled with alumina fiber (Saffil) batting to achieve
the desired thickness. The gap filler is stitched with Nextel thread, and the tail is reinforced with RTV
silicone adhesive. Stitched gap fillers can also include Nextel ceramic fiber braided sleeving, which
can be applied externally or internally to the folded area of the gap filler fabric.
Most gap fillers are installed after RSI tiles have been placed. The gap filler is bonded to the
underlying filler bar or tile sidewall using RTV silicone adhesive. After the adhesive cures, a friction
test is conducted to ensure proper compression within the gap and validate the bond integrity of the
gap filler. Pillow and pad-type gap fillers undergo a coating process that involves applying a high
emissivity ceramic coating in a two-part procedure similar to FI blankets. An initial precoat mixture,
consisting of 85% Ludox ammonia stabilized colloidal silica solution, 12% isopropyl alcohol, and 3%
silicon carbide powder, is applied and air-dried for 4 hours. This precoat enhances fabric adhesion for
the subsequent topcoat application, which consists of a mixture of Ludox ammonia stabilized colloidal
silica solution, silica powder, and silicon carbide powder. The topcoat is applied to the exposed area of
the gap filler and air-dried for 8 hours.
Ames gap fillers are available in three varieties, incorporating two fabric types and two coating
options. The fabric is offered in both non-vacuum baked and vacuum baked conditions. The non-
vacuum baked fabric allows for the application of black RTV coating for upper surface use and ceramic
coating for lower surface use. In contrast, the vacuum baked variety is exclusively fabricated with
black RTV coating for upper surface use.
Typically, the Ames gap filler is nominally 0.020 inches thick and is custom-cut to fit a correspond-
ing gap Mylar. For partial or complete gap filling, up to six layers of Ames gap fillers may be installed.
A Mylar template is crafted to mirror the length, width, and contour of the gap, with precise gap
measurements recorded at corresponding locations on the Mylar. The gap filler undergoes a prefitting
process, during which pull test loops are integrated. Subsequently, the gap filler is bonded using RTV
onto a primed surface, and the integrity of the bond is verified by pulling on the test loops after the
adhesive has cured [44].
7.3.8. Thermal Barriers
Thermal barriers serve a crucial role around penetrations and in the closeout areas between major
components of the orbiter. Their primary function is to limit the flow of hot gas to the underlying
cavity or structure. The specific locations of the orbiter ’s thermal barriers, along with aerothermal seals
are illustrated in Figure 15 (Thermal Barriers and Aerothermal Seal Locations) and 16 (Main Landing
Gear Door Thermal Barrier Detail) of the reference [44].
Thermal barriers typically consist of key elements such as spring tubes, insulative batting, sleeving,
and ceramic fabric. The spring tube, a tubular inconel wire mesh, is enclosed within braided sleeving
made of aluminoborosilicate fiber (Nextel). Following this, the thermal barrier is covered by an outer
layer crafted from Nextel ceramic fiber fabric. Depending on the specific type, the thermal barrier
is then attached to its designated cavity using its ceramic fabric tail (for adhesive-bonded varieties),
fastened to the structure through hardware (for mechanically attached types), or secured to a carrier
plate (for mechanically attached carrier panel types). The next figure illustrates the installation process
of the mechanically attached carrier panel type thermal barrier around the periphery of the main
landing gear doors [44].
The installation of thermal barriers involves specific processes tailored to unique design require-
ments. Typically, they are affixed under pressure to a solvent-cleaned and primed structural substrate
using RTV silicone adhesive. In the thermally extreme nose landing gear door area, external thermal
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barriers are bonded to the peripheral High-Temperature Reusable Surface Insulation (HRSI) tile side-
walls and Reinforced Carbon-Carbon (RCC) surfaces with a ceramic adhesive. This adhesive consists
of two components: the first is a mixture of 75% deionized water and 25% Ludox ammonia stabilized
colloidal silica solution, and the second is a ceramic adhesive powder.
For thermal barriers on the main landing gear and external tank doors, bonding takes place on
a solvent-cleaned and primed carrier panel using RTV silicone adhesive. The carrier panel is then
secured into a retaining fixture attached to the orbiter structure. Thermal barriers around the nozzles of
the Reaction Control System (RCS) thrusters are fastened to the structure using appropriate fasteners.
After installation, the outer fabric of the thermal barriers undergoes coating. This coating is
composed of either polyethylene or black RTV silicone adhesive, contributing to improved thermal
performance and durability.
7.3.9. Aerothermal Seals
Aerothermal seals are strategically utilized to regulate and limit the ingress of hot gases into the
cavities of control surfaces and payload bay doors. The specific locations of these aerothermal seals are
illustrated in the preceding figure. Notably, the areas where thermal seals are implemented include the
wing trailing edge/elevon leading edge (elevon cove) and the aft fuselage trailing edge/body flap
leading edge (body flap cove). The following figure provides a visual representation of the aerothermal
seal in the elevon cove region.
In the elevon cove, the primary seal is the span-wise polyimide seal, designed to make contact
with the elevon rub tube. Precise fitting against the rub tube is crucial for this seal to limit gas flow
into the cavity during control surface movement. Inside the cavity, the incorporation of heat sinks and
additional insulative material contributes to an increased thermal mass, effectively reducing structural
thermal gradients. To prevent hot flow from entering the cavity at the inboard and outboard ends of the
control surfaces, spring-loaded columbium seals are installed, thereby avoiding potential overheating
of the underlying structure and mechanisms. The spring-loaded seal accommodates the inboard and
outboard floating of the elevon due to thermal expansion mismatches between the wing and elevon.
To ensure a proper seal with the rub panels on the upper elevon, the upper surface of the elevon
cove is sealed with inconel flipper doors as shown in figure 17 (Elevon Cove Aerothermal Seal Detail
[
44
]) and 18 (Payload Bay Door Aerothermal Seals) of the reference [
44
]. These flipper doors, hinged
on the wing trailing edge, move in tandem with the elevon. The exposed metallic surface is coated
with white paint to optimize the thermal emissivity of the part.
The protection of the payload bay door area involves the use of two distinct types of aerothermal
seals, as illustrated in the upcoming figure. Expansion joints within this region are safeguarded by
environmental bulb seals. These seals, composed of FEP Teflon, are shielded during reentry by a
thermal barrier consisting of a quartz fibrous pile. To prevent water intrusion into the payload bay, the
sealing surfaces are coated with a fluorinated grease.
In the hinge area of the payload bay door, protection is ensured through a spring-loaded inconel
718 cover assembly. This assembly is deployed on the initial six hinges of OV-102 (Columbia) and the
initial ten hinges of OV-103 (Discovery), as well as on subsequent orbiters (Atlantis and Endeavour).
The design incorporates a floating mechanism, allowing for fore and aft movement of the graphite
epoxy composite payload bay doors to accommodate thermal expansion mismatches with the alu-
minum alloy midfuselage. The exposed surfaces of the hinge cover are coated with a high emissivity
Pyromark coating.
7.3.10. Windows
The orbiter is outfitted with eleven strategically positioned windows to facilitate mission opera-
tions, comprising six forward windows, two overhead windows, two aft flight deck windows, and
one crew hatch window, as depicted in the upcoming figure. The design of these windows features a
configuration where the forward, overhead, and crew hatch windows consist of three panes of glass
enclosed in a pressure-sealed retainer. The outermost pane is secured to the forward fuselage structure,
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while the inner two panes are attached to the crew module. In contrast, the aft flight deck windows
consist of two panes of glass solely attached to the crew module, with the outermost pane serving as
the sole window component of the thermal protection system.
The innermost pane, known as the pressure pane, is crafted from aluminosilicate glass, tempered
to endure the crew compartment’s on-orbit pressure differential. Capable of withstanding a pressure
of 8,600 psi at 240°F, this pane is coated with an infrared reflective coating on its outer surface. The
thickness varies, measuring 0.625 inches on forward windows, 0.450 inches on overhead windows,
0.300 inches on aft flight deck windows, and 0.250 inches on the crew hatch window.
The center pane, termed the redundant pane, is fashioned from low-expansion fused silica glass.
Uncoated, this pane has varying thicknesses: 1.300 inches on forward windows, 0.450 inches on
overhead windows, 0.300 inches on aft flight deck windows, and 0.500 inches on the crew hatch
window. The outermost pane, referred to as the thermal pane, is also made from fused silica glass
and is designed to withstand the same pressure as the pressure pane. Internally coated with a high-
efficiency anti-reflective coating to enhance light transmission, its thickness varies: 0.625 inches on
forward windows, 0.680 inches on overhead windows, and 0.300 inches on the crew hatch window.
For example, during the arrival of the Galileo spacecraft, ablation modeling predicted a higher
degree of ablation in the nose region compared to the shoulder area. However, the actual ablation
distances differed from the predictions based on data from ablation sensors. The measured thermal
protection system (TPS) recession at the shoulder area deviated by only 10 mm from the projected
values. Contrary to the anticipated 88 mm recession by the stagnation point recession model, the
measured value of the nose recession was 41 mm.
High-temperature reusable surface insulation (HRSI), commonly known as silica ceramic tiles,
was developed for the Space Shuttle and can withstand re-entry temperatures of up to 1,260 °C (2,300
F). While flexible and available in various densities, HRSI tiles are fragile and prone to breakage,
requiring a waterproof coating. Toughened unpiece fibrous insulation (TUFI) tiles, in comparison
to HRSI tiles, offer greater strength and hardness. Both the Space Shuttle and the X-37B Orbital Test
Vehicle employ a similar heat shielding strategy. Lightweight tiles are used on the belly, while flexible
insulation blankets are used in colder regions.
In areas where re-entry temperatures remain below 649 °C (1,200 °F), quilted blankets composed
of woven silica fiber, silica batting, and aluminoborosilicate fiber were employed on the Space Shuttle,
effectively providing thermal protection. A critical element of the Space Shuttle, especially in the nose
cap and wing leading edges, was reinforced carbon-carbon (RCC), capable of withstanding re-entry
temperatures exceeding 1,260 °C (2,300 °F). Although not flown, a different composite material known
as carbon/silicon carbide (C/Sic), comprising carbon fibers embedded in a silicon carbide matrix, was
ground-tested for potential use in the X-38 vehicle’s nose cap, leading edges, and steering flaps.
To shield carbon/carbon composites from oxidation, multilayer high-temperature ceramics like
silicon carbide and zirconium boride, as well as nanocomposites, can be utilized. Ablative heatshields
typically employ a honeycomb structure with resin or polymer injected into each cell. Various ablative
materials, including Av coat (used on Apollo capsules), phenolic-impregnated carbon ablator (PICA,
used by the Stardust sample return capsule), and SLA-561V (used on Viking landers), have been
employed. These materials are designed to gradually erode and release heat during re-entry, providing
effective thermal shielding.
Recent investigations have provided valuable insights for advanced thermal protection system
(TPS) strategies in aerospace re-entry applications. Moreover, Re-entry missions face challenges
from high temperatures, plasma interactions, ultraviolet (UV) radiation, and atomic oxygen (AO),
necessitating robust material design for thermal protection systems (TPS). Carbon/Carbon (C/C)
composites are favored for their thermal stability, yet their rapid degradation in oxidizing environments
highlights the need for protective coatings. Researchers evaluated the effects of AO exposure on C/C
composites, demonstrating that coated materials significantly withstand erosive damage compared
to uncoated ones. A novel nano-reinforced aluminum oxide varnish, enhanced with silicon dioxide
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nano-spheres, proved to effectively shield these composites, underscoring the importance of coating
optimization for enhanced durability in aerospace applications [45].
In another study, researchers evaluated an innovative thermal protection system (TPS) concept by
introducing a hybrid multiscale ceramic coating, specifically an alumina-based varnish enhanced with
silica nanoparticles, designed for application on Carbon/Carbon (C/C) plates. The treatment aimed to
maintain the thermo-mechanical integrity of the ceramic substrate under challenging space environ-
ment conditions, including the thermal cycling characteristic of Low Earth Orbit (LEO), outgassing
resulting from ultra-high vacuum, and exposure to atomic oxygen and ultraviolet (UV) radiation. To
assess the thermal performance and stresses on both the substrate and the coating layer, experimental
measurements of the coefficient of thermal expansion (CTE) were conducted [46].
7.4. Features and Upgrades
The space shuttle Enterprise was designed without a fully functional thermal protection system.
Instead, its surface was mainly covered with simulated tiles made from polyurethane foam, while
fiberglass was used for the leading-edge panels in place of the reinforced carbon–carbon material
found on spaceflight-ready orbiters. Columbia, the first operational orbiter in the fleet, was the first to
incorporate High and Low Temperature Reusable Surface Insulation (HRSI/LRSI) tiles as its primary
thermal protection system (TPS). Additionally, white silicone rubber-painted Nomex, known as Felt
Reusable Surface Insulation (FRSI) blankets, was applied in certain areas, including the wings, fuselage,
and payload bay doors [47].
Subsequent upgrades to the shuttle fleet included replacing many of the white LRSI tiles on upper
surfaces with Advanced Flexible Reusable Surface Insulation (AFRSI) blankets, also referred to as
Fibrous Insulation Blankets (FIBs), which had already been used on Discovery and Atlantis [
48
]. These
AFRSI blankets were constructed with layers of pure silica felt sandwiched between an outer silica
fabric layer and an inner S-Glass fabric layer, stitched together using pure silica thread in a 1-inch grid.
The blankets were then coated with a high-purity silica layer, making them semi-rigid and allowing
them to be manufactured in sizes as large as 30 inches by 30 inches. Each blanket replaced up to 25
individual tiles and was bonded directly to the orbiter’s surface [
47
]. The direct application of these
blankets resulted in multiple benefits, including a significant reduction in weight, enhanced durability,
lower fabrication and installation costs, and a shorter installation schedule [48].
The Challenger orbiter, along with later orbiters, had fewer tiles in its Thermal Protection System
than Columbia. However, Challenger still featured an extensive use of white LRSI tiles on the cabin
and main fuselage. Many tiles on the payload bay doors, upper wing surfaces, and rear fuselage were
replaced with DuPont white Nomex felt insulation. These design modifications, combined with a
lighter overall structure, enabled Challenger to carry 2,500 lb (1,100 kg) more payload than Columbia.
Additionally, the fuselage and wings of Challenger were both stronger and lighter than those of its
predecessor [49].
During the construction of Discovery, a unique feature emerged near the middle starboard
window where black tiles were placed instead of the expected white ones. It remains unclear whether
this was a manufacturing anomaly or a deliberate choice, but this feature, often referred to as the
“teardrop,” provided a distinct identifier for Discovery within the shuttle fleet, even though it was
not always immediately noticeable to casual observers [?]. Weight optimization efforts for Discovery
included an increased use of quilted AFRSI blankets rather than white LRSI tiles on the fuselage.
Additionally, the payload bay doors and certain wing spars and beams were constructed from graphite
epoxy instead of aluminum, further reducing weight [50].
Similarly, Atlantis underwent several weight-reduction modifications, including the replacement
of AFRSI insulation blankets on upper surfaces with FRSI, further enhancing its efficiency and overall
structural performance [48].
Table 1shows an idea of how many and how much area each type of installation takes up on the
orbiter. Further, Figure
??
gives an approximate location of each tile and insulation type for the shuttle.
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Table 1. Approximate amount of tiles used on each orbiter and for the blankets and approximate amount of
square feet used.
AFRSI + FRSI HRSI LRSI FRCI
˜
1,800 sq. ft. ˜
20,500 ˜
800 ˜
3,000
Every tile undergoes meticulous inspection both prior to launch and after re-entry to verify its
suitability for another flight. If a tile is deemed unfit for further use, it is promptly replaced with a new
one. This rigorous inspection process is paramount to ensuring the safety of the orbiter’s occupants.
Rockwell employees can be seen conducting a thorough inspection of a tile before launch as shown in
figure 2 in the reference [?].
8. Design and Material Requirements for Spacecraft
8.1. Considerations for Manufacturability: Importance of Traceability and Record-Keeping in Aerospace
In the aerospace industry, meticulous record-keeping and traceability play a crucial role in
ensuring safety, quality control, and regulatory compliance. A robust part identification and traceability
system is essential for recording the complete history of materials used in critical aerospace applications.
By maintaining detailed documentation, engineers can verify that materials meet specified standards
and have undergone the necessary treatments and inspections. This is particularly important for
materials susceptible to batch variations or hydrogen embrittlement, as traceability helps mitigate the
risk of failure. Furthermore, comprehensive records facilitate compliance with industry regulations
and standards during audits and inspections. Ultimately, accurate documentation and traceability
contribute significantly to mission success and the upholding of aerospace standards.
Vendors in the aerospace sector must have a deep understanding of approval criteria for fracture-
critical hardware. A notable case underscores the severe consequences of non-compliance. Over
a period of sixteen years, a NASA contractor was found guilty of improperly heat-treating, aging,
and falsifying quality tests on aerospace hardware used in major programs, including the Space
Shuttle, Space Station, commercial and military aircraft, and missile programs. This led to significant
legal penalties and highlighted the critical role of adherence to proper procedures in aerospace
manufacturing.
8.2. Fracture Control and Non-Destructive Evaluation (NDE)
Ensuring the safety and reliability of space vehicle systems requires rigorous fracture control
measures. Every spacecraft component must be thoroughly assessed to determine the likelihood of
structural failure and its potential catastrophic consequences. If a component is identified as having the
potential for catastrophic failure, comprehensive fracture control measures, including non-destructive
evaluation (NDE), are implemented. Various NDE techniques, such as eddy current testing, fluorescent
penetrant inspection, magnetic particle testing, radiography, and ultrasonics, are used to detect flaws
or cracks. However, certain non-structural components, such as insulating blankets, electrical wiring
bundles, and elastomeric seals, which are resistant to crack propagation, may be exempt from fracture
control criteria.
This case serves as a critical reminder of the importance of adhering to stringent procedures and
maintaining high standards in aerospace manufacturing, particularly for fracture-critical hardware.
It underscores the necessity of using precise and reliable methods to detect and manage potential
failures, thereby ensuring the structural integrity and safety of spacecraft and other aerospace systems.
8.3. Designing for Manufacturability in Spacecraft Engineering
Incorporating manufacturability considerations into spacecraft component design is essential to
optimizing production efficiency and reducing costs. The concept of manufacturability plays a key
role in minimizing manufacturing expenses while adhering to strict project timelines. To achieve this,
various factors must be taken into account during the design phase. Table 2presents a summary of
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list for manufacturability aspects that designers should consider. By integrating manufacturability
principles early in the design process, engineers can enhance production effectiveness, streamline
fabrication processes, and improve overall project outcomes.
Table 2. Key Considerations for Manufacturability in Aerospace Design.
Factor Description
Material Selection
Choosing materials that balance performance, cost, and ease of fabrication
Process Compatibility Ensuring component design aligns with available manufacturing
techniques
Tolerance Control Designing with achievable tolerances to reduce rework and inspection
time
Assembly Efficiency Simplifying assembly processes to minimize labor and production time
Inspection and Testing Incorporating features that facilitate non-destructive evaluation and
quality assurance
By proactively addressing manufacturability concerns in the initial design stages, aerospace
engineers can significantly enhance the efficiency and effectiveness of spacecraft production, leading
to improved mission reliability and cost-effectiveness. Further, a number of elements need to be
considered in order to assure manufacturability. These elements are listed in Table 3, which offers a
thorough list of aspects for designers to take into account. Engineers can increase the efficacy and
efficiency of producing spaceship components by adding manufacturability early in the design phase,
which will improve project outcomes overall are as follows:
Table 3. Comprehensive overview for the considerations for manufacturability.
Factor Consideration
Drawings
Utilise geometric tolerancing and dimensioning Do not use double
dimensions.
select dimensions that are similar to typical stock
If at all possible, choose 45° as opposed to 40° for your angles. Just use the
necessary number of decimal places.
If a portion requires complicated masking or many processes, make a
separate drawing for finishing.
Tolerances Use reasonable tolerance thresholds Keep in mind the tolerance stickup
Think about access to locations for inspection and tool use.
Drilled Holes
only tap holes that are 1.5 times the diameter or less in size
Consider thread relief or refrain from tapping the bottom of blind holes to
avoid burr accumulation.
Inside Radii provide the biggest possible radii
wherever possible, use the same radius
Edges or Thickness Reduce any breakable sharp edges or points.
Avoid deep holes and thin walls to reduce distortion.
Part Holding
Extra stock should be available on all sides so the work piece can be clamped
or chucked.
Assembly built to be disassembled
Set aside space for wrenches Whenever necessary, include access holes
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Table 3. Cont.
Factor Consideration
Materials
choose materials that are easy to manufacture using
Be aware that some materials aren’t available in your country and that some
certifications can be hard to come by or aren’t valid.
Choose materials that can be processed quickly through machining, heat
treatment, etc..
Select materials with the simplest storage requirements
Processes
choose techniques that have been validated and are accessible to production
Composite
Resources
Make sure to choose a material system where manufacturing has experience
and tested procedures.
Surface Finishes Set minimum completions
Coatings
Utilize proven production techniques.
Before choosing the best practice, consult coating experts, production, and
engineering.
Think about how coating procedures affect things like part size and optical
characteristics.
Take coating holes, blind holes, and challenging masking needs into
consideration.
If the masking is difficult, use coating-specific drawings.
Heat Treat
Consider using precipitation hardening alloys such as 17-4PH, 15-5MO,
12-8MO which only require a relatively low temperature of 480-620 °C
(900-1150 ºF) soak from one to four hours with an air cool in place of the
common alloys like 4340 or 4130 steels, which require an austenitizing soak
at 815-843 °C (1500-1550 ºF) with a quick quench into oil followed by a
tempering soak 480-600 °C (900-1100 ºF).
With the latter kind of heat treatment, there is substantial oxidation and
scaling.
If the weldment has tight tolerances or a poor surface quality, you should
increase the weld size or add gusseting rather than using heat treatment to
restore it to a T6 condition. This calls for a rapid quench after a solution
treatment at nearly melting temperature.
Welding
When feasible, use the American Welding Society Standard Welding
Procedure Specifications.
minimize the length of the weld
Choose a joint that has the least amount of filler. Avoid over welding
For structural applications, use square tubing rather than round tubing.
Design for accessibility and inspection
Be prepared for distortion and shrinking.
Be mindful of the uneven dimensions of the mill-supplied structural I and H
beams when employing them, and spell out your tolerances appropriately.
When the beams can vary, a +/-.030" tolerance is challenging to maintain.
From the center line to the end of the flange, 250".
Painting
Make sure that processes are available that have been documented and
verified. Maintain a suitable level of surface cleanliness
Think about your capacity to hold a paintbrush perpendicular to the surface
you’re painting.
Shop Capability
dimensions and component weight Limits for forklifts and cranes
verified/documented procedures Welding techniques
Sheet metal proficiency capacity for surface treatment sizes after heating
Size restrictions for painting or cleaning.
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Table 3. Cont.
Factor Consideration
Electrical or
Electronic
Components
Take lead time needs and production capacity into account.
Storage and
Packaging
Requirements
the component’s size needed environmental controls
space and tools readily available to accommodate storage needs
During production, component shelf life must be taken into account. Organic-based materials
have a finite shelf life as well as a finite static age life, or the amount of time they may spend in
an ambient environment without operating. Even when materials are sealed, the characteristics of
polymeric resins, catalysts, some lubricants, thin polymer films, sealants, adhesives, and elastomers can
slowly deteriorate over time. The shelf life is typically indicated by manufacturers; however, storage
circumstances are sometimes not. In general, lower storage temperatures and limiting exposure to
light (including fluorescent lighting and sunshine) increase shelf life. The amount of time the product
has been exposed to the elements in it, such as oxygen, moisture, and other active agents, also affects
how long it will last on the shelf.
8.4. Considerations for Flammability, Toxicity, and off Gassing
All materials used in spacecraft and ground support equipment must comply with NASA-
STD-6001 (formerly NHB 8060.1), which outlines requirements and test procedures for flammability,
off-gassing, and material compatibility. These standards ensure the safety and reliability of materials
in various operational environments, including habitable spacecraft interiors, liquid oxygen (LOX)
and gaseous oxygen (GOX) systems, breathing gases, and reactive fluids.
Based on the intended application, the specific tests required for each environment are detailed
in Table 1 of NASA-STD-6001. Additionally, NASA maintains the Materials and Processes Technical
Information System (MAPTIS), an online database containing material test results and evaluations.
Beyond Newtonian fluids, numerous industrial and biological systems involve non-Newtonian
fluids, whose viscosity varies with shear rate, time, or applied stress. These fluids exhibit complex flow
behavior, particularly under high-pressure or high-shear environments. For example, shear-thinning
fluids—such as polymer solutions—experience a decrease in viscosity with increasing shear rate,
facilitating enhanced flow rates under dynamic conditions [
51
,
52
]. In contrast, shear-thickening flu-
ids—such as concentrated suspensions and colloidal dispersions—undergo a sudden rise in viscosity at
elevated shear rates [
53
], which can destabilize flow or impede transport. Yield stress fluids, including
Bingham plastics and viscoplastic materials, require a minimum threshold stress to initiate flow. Their
yielding and spreading behaviors are significantly influenced by pressure and external forces, playing
a critical role in applications like hydraulic fracturing and extrusion-based manufacturing [54,55].
Understanding these behaviors is especially crucial when selecting or engineering materials and
fluids for space applications governed by NASA-STD-6001, where interactions with high-pressure,
reactive, or oxygen-rich environments may amplify non-Newtonian effects. Hence, integrating rheolog-
ical characterization with safety compliance testing becomes essential for ensuring both performance
and mission safety.
A critical test defined by NASA-STD-6001 is the upward flame propagation test (Test 1), which
assesses the fundamental flammability of materials. Managing flammability risks in space hardware
is essential for crew safety. Lessons learned from the Apollo 1 fire incident in 1967 emphasized two
crucial principles: avoiding propagation pathways and recognizing that ignition sources can never
be completely eliminated. By restricting primary propagation routes, any potential fire will remain
localized and self-extinguish, minimizing risks to both the crew and spacecraft systems. Additionally,
the total volume of combustible materials should be kept as low as possible to further reduce hazards.
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To support flammability control, additional guidelines are provided in documents such as NSTS
22648, which addresses flammability configuration analysis for spacecraft applications, and MSFC-
PROC-1301, which outlines material control procedures. These protocols help engineers implement
material selection and design strategies that enhance fire safety in space missions.
Table 4. NASA-STD-6001 Requirements and Additional Tests for Each Material Use. The terminology used in
the table are: S – Supplemental Test; R – Required Test. 2–Only surface areas bigger than 4 ft2 (0.37 m2) each use
require a test. 3– Materials in hermetically sealed containers are exempt from this requirement (see Section 2.1.3).
4–If the items meet the requirements of Test 1 in that setting, they are not necessary contains every place that isn’t
inside the liveable flight compartment.
Environment Test No. Type Title
Habitable Flight 1 R Upward Flame Propagation
3 S Flash Point of Liquids
4 6 7 R R3 R3 Assessing the flammability, odour, and off-gassing
potential of electrical wire insulation
8 S Flammability Test for Materials in
sealed containers with vents
10 S Simulated Panel or Major Assembly
Flammability
12 S Total Off gassing of Spacecraft
18 R 18 R Arc-Tracking
Other Areas 5 1 R Upward Flame Propagation
2 R2/S Heat and Visible Smoke Release Rates
3 S Flash Point of Liquids
4 R Electrical Wire Insulation Flammability
8 S Flammability Test for Materials in
Vented or Sealed Containers
18 R Arc-Tracking
LOX and GOX 6 R3 Odor Assessment
Environments 7 R3 Determination of Off gassed Products
13A R Mechanical Impact for Materials in
13B R
Mechanical Impact for Materials in Variable Pressure LOX
and GOX
14 S Pressurized Gaseous Oxygen Pneumatic Impact for
Nonmetals
17 R4 Upward Flammability of Materials in GOX
Breathing Gases 1 R Upward Flame Propagation
6 R Odor Assessment
7 R Determination of Off gassed Products
13A R Mechanical Impact for Materials in
13B R Mechanical Impact for Materials in
Reactive Fluids 15 R
Materials with Variable Pressure LOX and GOX Reactivity
in Aerospace Fluids
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NASA-STD-6001 includes several critical tests to assess the safety and reliability of materials used
in spacecraft. One such test, Step 4, evaluates the flammability of electrical wire insulation. Awareness
of insulation wear and abrasion increased significantly after an electrical fire occurred aboard STS-61-A
Spacelab D-1 in 1985. In that incident, frayed insulation led to a short circuit and fire, yet the circuit
breaker failed to trip. This event underscored the importance of ensuring that electrical breakers are
easily accessible to quickly cut power to malfunctioning equipment. Furthermore, lessons from the
1997 fire in a Russian oxygen generator aboard the Mir space station prompted the implementation
of containment shields and stricter quality controls for oxygen canisters on the International Space
Station.
To evaluate the off-gassing characteristics of materials, NASA-STD-6001 includes Tests 7 and
12. These assessments are essential for maintaining air quality in habitable areas of spacecraft and
minimizing the presence of trace contaminants. Non-metallic materials such as coatings, adhesives,
and potting compounds can release volatile organic compounds, including formaldehyde, n-butanol,
and aliphatic aldehydes, which may pose risks to crew health. Although activated carbon filters can
remove some contaminants, long-duration human missions should not rely solely on filtration. A
recommended practice to reduce off-gassing is to subject materials to a bakeout procedure, typically
conducted at 50 °C (122 °F) for 48 hours, to eliminate volatile compounds before integration into the
spacecraft.
There are two primary categories of material testing based on the operational environment:
off-gassing and outgassing. External spacecraft components undergo outgassing testing in vacuum
conditions following ASTM-E-595, which measures total mass loss (TML) and collected volatile
condensable material (CVCM). The recommended limits are 1.0% TML and 0.1% CVCM. Depending
on the spacecraft’s contamination control plan, additional testing under ASTM-E-1559 may be required.
This test provides data on outgassing rates over time at varying temperatures, enhancing dynamic
modeling of potential contaminants and ensuring that materials meet strict volatility standards to
maintain spacecraft cleanliness.
For materials exposed to sensitive optical surfaces in space, MSFC-SPEC-1443 outlines specific
outgassing tests. This standard was developed during the Hubble Space Telescope program to
ensure that materials meeting ASTM-E-595 standards do not emit volatiles that could degrade optical
performance in the ultraviolet spectrum. A material is deemed unsuitable if it causes more than a 3%
change in reflectance of a magnesium fluoride/aluminum mirror before and after vacuum exposure.
These stringent testing protocols are essential to preserving optical integrity and overall spacecraft
performance.
9. Structural Materials
When selecting structural materials for spacecraft, the strength-to-weight ratio plays a critical
role. Engineers must account for both static and dynamic loads that the spacecraft will encounter.
Additional key considerations include thermal performance, corrosion resistance, manufacturability,
reparability, and cost. To ensure materials meet the necessary requirements, engineers frequently refer-
ence established resources such as the Metallic Materials Properties Development and Standardization
(MMPDS, formerly MIL-HDBK-5), MIL-HDBK-17 for plastics in flight vehicles, and MIL-HDBK-23
for structural sandwich composites. These sources provide essential data on material properties for
aerospace applications.
Beyond general material properties, use-dependent characteristics must also be considered. For
instance, the dielectric constant is crucial when designing radomes, while gas permeability becomes sig-
nificant in the construction of fuel tanks. A comprehensive evaluation of these factors enables engineers
to make informed decisions that ensure the structural integrity and performance of spacecraft.
High-strength alloys, including titanium, aluminum, and stainless steel, have been widely used in
aerospace applications. However, certain limitations must be noted. Aluminum alloys from the 5000
series containing more than 3% magnesium should not be used at temperatures exceeding 66 °C (150
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°F) due to the risk of exfoliation or stress-corrosion cracking caused by grain boundary precipitation.
Examples of such alloys include 5086-H34, 5086-H38, 5456-H32, and 5456-H38. Similarly, the 300-series
corrosion-resistant stainless steels should not be used for prolonged periods above 370 °C (700 °F).
Austenitic stainless steels provide superior resistance to stress corrosion cracking compared
to ferritic and duplex stainless steels, primarily due to their higher chromium and nickel content.
Additionally, nickel-based alloys and titanium alloys generally exhibit strong resistance to stress
corrosion cracking. However, copper alloys containing more than 20% zinc may still be vulnerable,
even with alloying elements designed to improve resistance. MSFC-STD-3029 provides guidelines for
material selection in sodium chloride environments, emphasizing that protective coatings can only
delay, rather than prevent, stress corrosion. Additionally, surface modifications such as carburizing or
nitriding can increase susceptibility to stress corrosion cracking.
Aluminum-lithium alloys offer a weight reduction of 10% or more compared to conventional
aerospace aluminum alloys. A notable application of these materials was in the Space Shuttle’s Super
Lightweight Tank (SLWT), which reduced weight by 7,000 lbs compared to the original External Tank.
Friction stir welding has enabled the successful joining of aluminum-lithium and other previously
challenging aluminum alloys. This process reduces weld defects, eliminates the need for inert shielding
gas or filler material, and produces stronger joints compared to traditional fusion welding.
Composite materials are frequently used in applications requiring precise thermal expansion
tolerances, such as telescope optical benches. Several types of fibers—including graphite, boron,
fiberglass, aramids, and carbon—can be used as reinforcements, bound by polymer resin systems such
as epoxy, phenolic, polyimide, and polysulfone. These fibers can be arranged in various configurations,
including tow, tape, sheet, or woven forms. For applications demanding high toughness, metal-matrix
composites (MMCs) and ceramic-matrix composites (CMCs) are employed, utilizing particle or fiber
reinforcement in forms such as chopped fibers, whiskers, or continuous and discontinuous fibers.
Non-metallic materials in low Earth orbit (LEO) are susceptible to degradation from atomic oxygen
exposure. This exposure can lead to surface erosion, particularly in thin composites. Additionally,
polymeric materials may undergo chain scission or cross-linking when exposed to ultraviolet (UV)
and particle radiation, potentially compromising structural integrity. For example, composites on
the leading edge of the Long Duration Exposure Facility (LDEF) satellite lost an entire layer due to
prolonged exposure to atomic oxygen over 5.8 years. Some polymeric materials may also weaken and
become brittle in high-radiation environments, making careful material selection essential.
Due to their high stiffness-to-weight ratio, honeycomb structures are widely used in aerospace
applications. These structures utilize facesheets and cores made from either metals or composite
materials. Depending on the application, closed-cell cores may be necessary to prevent cryopumping
in cryogenic conditions. Cryopumping occurs when gas liquefies and condenses at cryogenic tempera-
tures, creating a vacuum that can lead to unintended fluid movement. A key example was observed in
the X-33 honeycomb composite fuel tank, where liquid hydrogen escaped through microcracks in the
inner facesheet, while nitrogen purge gas was drawn in through microcracks in the outer facesheet.
Incorporating redundant permeation barriers is essential to mitigating such risks.
The selection of spacecraft structural materials requires a meticulous evaluation of multiple
factors, including mechanical performance, environmental resistance, and manufacturability. While
traditional metal alloys such as aluminum, titanium, and stainless steel continue to play a vital
role, advancements in composites, aluminum-lithium alloys, and friction stir welding have enabled
significant improvements in performance and weight reduction. Engineers must also account for the
unique challenges of the space environment, including atomic oxygen erosion, radiation-induced
degradation, and cryogenic effects. By leveraging established material databases and standards,
aerospace engineers can make informed decisions that enhance the safety, durability, and efficiency of
spacecraft structures.
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10. Challenges and Future Prospects in Space Shuttle Materials
The materials used in the space shuttle encountered several challenges, primarily the need for
high-performance materials capable of withstanding the extreme conditions of space. These conditions
include exposure to extreme temperatures, vacuum, radiation, micrometeoroid impacts, and space
debris. Additionally, these materials had to meet stringent safety and reliability standards to ensure
the success of human spaceflight missions. Another crucial requirement was minimizing weight, as
reducing the overall mass of the spacecraft directly impacted the amount of propellant required for
launch, thereby enhancing mission efficiency.
Despite significant progress in materials science and engineering, ongoing research continues to
address challenges and explore new opportunities for future advancements in space materials. One
key area of research involves the development of advanced composites with superior mechanical
properties, enhanced thermal stability, and reduced outgassing to improve performance in space
environments. These next-generation materials aim to provide greater durability while maintaining
low weight. Another critical focus is on thermal protection materials, where research is directed
toward creating lightweight yet highly heat-resistant materials capable of withstanding the extreme
temperatures experienced during atmospheric re-entry. The objective is to develop materials that
minimize weight and thickness without compromising thermal protection capabilities.
The use of nanomaterials, such as carbon nanotubes and graphene, presents another promising
avenue for space applications. These materials exhibit exceptional properties, including superior
strength, high thermal conductivity, and enhanced radiation resistance, which could significantly im-
prove spacecraft structural components and shielding materials. Additionally, additive manufacturing,
or 3D printing, is emerging as a transformative technology in space material fabrication. This approach
enables the production of complex and lightweight structures with customized properties, optimiz-
ing material usage and reducing manufacturing constraints for space applications. Sustainability is
also gaining increasing attention in space exploration. Research is exploring the use of recyclable,
biodegradable, and renewable materials to minimize the environmental impact of space missions. The
incorporation of environmentally friendly materials into spacecraft components could contribute to
long-term sustainability in space exploration by reducing waste and enabling resource-efficient mission
designs. In summary, while significant advancements have been made in space shuttle materials, ongo-
ing research continues to push the boundaries of material science. By developing advanced composites,
high-performance thermal protection systems, nanomaterial-based enhancements, and sustainable
materials, the future of space exploration materials is poised to improve spacecraft durability, efficiency,
and environmental sustainability.
11. New Directions in Space Exploration
The evolution of space exploration post-Space Shuttle program has ushered in new directions for
both robotic and human endeavors in the cosmos. Building on the foundation of the Shuttle, which
facilitated significant technological advancements and international collaboration, current programs
are now focusing on returning humans to the Moon through NASA’s Artemis initiative. This program
aims not only to establish a sustainable base on the Moon but also to prepare for future crewed missions
to Mars [56].
Moreover, private space companies have emerged as integral players in space exploration, en-
hancing the democratization and accessibility of space travel. Advancements in human-computer
interaction (HCI) systems are being designed to support a diverse range of missions, enabling better
human integration in space environments [
57
]. Additionally, innovative research in areas such as space
life sciences is expanding our understanding of how biological systems adapt to space conditions,
furthering efforts to cultivate food in space through fermentation processes [
58
]. As space exploration
continues to evolve, interdisciplinary approaches integrating biology, technology, and engineering are
crucial. Ongoing research focusing on plant growth in microgravity and the adaptation of immune
responses under space conditions underscores the transformative potential of space research [
59
,
60
].
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Together, these advancements signify a new era in space exploration that builds on past achievements
while reaching towards the future.
12. Conclusions
In conclusion, the significance of advanced insulation techniques and materials in the optimal
functioning of the space shuttle within challenging environments cannot be overstated. The meticulous
selection and design of materials, such as reinforced carbon-carbon (RCC) and ceramic tiles comprising
the Thermal Protection System (TPS), play a pivotal role in safeguarding the spacecraft from extreme
temperatures, particularly during re-entry. The collective effort of insulation blankets, cryogenic
insulation, structural insulation, and active thermal control systems contributes to maintaining the
requisite temperature range for diverse spacecraft components. The proper application of insulation
materials is fundamental to ensuring the safety, reliability, and overall performance of the space shuttle.
As we look ahead, continuous research and development in insulation materials and techniques remain
imperative for the advancement of spacecraft designs. The ongoing challenges and opportunities in
materials for space applications underscore the need for exploration into innovative realms, including
the evolution of composites, nanomaterials, additive manufacturing, and sustainability. Embracing
these avenues will not only address current challenges but also pave the way for enhanced capabilities
and resilience in future space exploration endeavors
References
1.
Garg, A. Pulsatile pressure enhanced rapid water transport through flexible graphene nano/Angstrom-size
channels: a continuum modeling approach using the micro-structure of nanoconfined water. New Journal of
Physics 2023,25.
2. Garg, A. Enhanced flow in deformable carbon nanotubes. Journal of Applied Physics 2024,135.
3.
Garg, A.; Prasad, P. Wall-slip effects on the yield-stress fluid flows in the rigid and deformable channel.
ChemRxiv- Polymer Science, DOI: 10.26434/chemrxiv-2023-l3knn 2023, pp. 1–30.
4.
Garg, A.; Poddar, D.; Ahmad, F.; Pattanayek, S.K.; Goel, G. Elastoviscoplastic Model of Shellac-Butanol
Solutions and its Application in Coated Paper Barrier Property Analysis 2025.https://doi.org/10.26434
/chemrxiv-2025-sfckm.
5.
Abd El-Hameed, A.M.; Abdel-Aziz, Y. Aluminium Alloys in Space Applications: A Short Report. Journal of
Advanced Research in Applied Sciences and Engineering Technology 2021,22, 1–7.
6.
Olivas, J.; Wright, M.; Christoffersen, R.; Cone, D.; McDanels, S. Crystallographic oxide phase identification
of char deposits obtained from space shuttle Columbia window debris. Acta Astronautica 2010,67, 553–560.
7.
Ochoa, N.U.; Smith, A.; Cone, D.; Stafford, S.; Olivas, J. Investigation of material response to atmospheric
re-entry exposure of sub-structural Ti-6Al-4V components recovered from Space Shuttle Columbia. Journal
of Space Safety Engineering 2021,8, 113–120.
8. Lyle, K.H.; Fasanella, E.L. Permanent set of the space shuttle thermal protection system reinforced carbon–
carbon material. Composites Part A: Applied Science and Manufacturing 2009,40, 702–708.
9.
Ince, J.; Peerzada, M.; Mathews, L.; Pai, A.; Al-Qatatsheh, A.; Abbasi, S.; Yin, Y.; Hameed, N.; Duffy, A.; Lau,
A.; et al. Overview of emerging hybrid and composite materials for space applications. Advanced Composites
and Hybrid Materials 2023,6, 130.
10.
Alpert, B.K.; Johnson, B.J. Extravehicular activity framework for exploration-2019. In Proceedings of the
International Conference on Environmental Systems, 2019, number JSC-E-DAA-TN70005.
11.
Degtyarev, A.; Lobanov, L.; Kushnar’ov, A.; Baranov, I.Y.; Volkov, V.; Perepichay, A.; Korotenko, V.; Volkova,
O.; Osinovyy, G.; Lysenko, Y.A.; et al. On possibilities for development of the common-sense concept of
habitats beyond the Earth. Acta Astronautica 2020,170, 487–498.
12.
Naser, M.Z.; Chehab, A.I. Materials and design concepts for space-resilient structures. Progress in Aerospace
Sciences 2018,98, 74–90.
13. Garg, A. Aerodynamics. In Proceedings of the GATE Aerospace Forum Educational Services, 2015.
14. Garg, A. Aircraft Propulsion. In Proceedings of the GATE Aerospace Forum Educational Services, 2015.
15.
Kim, H.S. The Characterization of the Selected Materials for Space Shuttle. In Proceedings of the 9th
Asia-Pacific Microscopy Conference (APMC9) in conjunction with the 39th Annual Meeting of the Korean
Society of Microscopy, 2008, number KSC-2008-033.
Preprints.org (www.preprints.org) | NOT PEER-REVIEWED | Posted: 22 April 2025 doi:10.20944/preprints202402.0382.v2
30 of 31
16.
Vishal, G.; Garg, A.; Sarkar, J.; Pattanayek, S.K. The channel flow of a real shear thickening fluid using the
Lattice Boltzmann Simulation and the Theoretical Model. ChemRxiv- Chemical Engineering and Industrial
Chemistry, DOI: 10.26434/chemrxiv-2023-zk1nn 2023, pp. 1–26.
17.
Vishal, G.; Garg, A.; Sarkar, J.; Pattanayek, S.K. Real Shear Thickening Fluid (STF) Flow in Converging-
Diverging Channels: Analytical and Lattice Boltzmann Study. ChemRxiv- Chemical Engineering and Industrial
Chemistry, DOI: 10.26434/chemrxiv-2023-3cjvq 2023, pp. 1–29.
18.
Vishal, G.; Garg, A.; Sarkar, J.; Pattanayek, S.K. Modelling of Real Shear Thickening Fluid (STF) Flow around
a Circular Cylinder within a Channel using the Lattice Boltzmann Method. ChemRxiv- Chemical Engineering
and Industrial Chemistry, DOI: 10.26434/chemrxiv-2024-nzpxr 2024, pp. 1–19.
19. Tavassoli, A. Metallic materials for the space shuttle. The Aeronautical Journal 1972,76, 152–156.
20.
Finckenor, M.M., Document ID 20160013391. In Aerospace Materials and Applications; American Institute of
Aeronautics and Astronautics, 2018. NASA Marshall Space Flight Center Huntsville, AL, United States,
https://doi.org/10.2514/4.104893.
21.
Zhang, X.; Chen, Y.; Hu, J. Recent advances in the development of aerospace materials. Progress in Aerospace
Sciences 2018,97, 22–34.
22.
Basheer, A.A. Advances in the smart materials applications in the aerospace industries. Aircraft Engineering
and Aerospace Technology 2020,92, 1027–1035.
23. Sivolella, D. Space Shuttle in Uniform; Springer, 2017.
24.
Council, N.R.; et al. Materials Needs and R&D Strategy for Future Military Aerospace Propulsion Systems;
National Academies Press, 2011.
25.
Rajput, A.; Upma.; Shukla, S.K.; Thakur, N.; Debnath, A.; Mangla, B. Advanced Polymeric Materials for
Aerospace Applications. Aerospace Polymeric Materials 2022, pp. 117–136.
26.
Golfman, Y.; Sudbury, M. Spray Deposition of Aerogels as a Thermal Insulation for the Space Shuttle Fuel
Tanks. An International Journal of Processing, Science, Characterization and Application of Advanced Materials
2007, p. 42.
27.
Franz, G.; Hassan, M.H. Structural Health Monitoring of Laminated Materials for Aerospace Application. In
Structural Integrity and Monitoring for Composite Materials; Springer, 2023; pp. 1–26.
28.
Norkhairunnisa, M.; Chai Hua, T.; Sapuan, S.; Ilyas, R. Evolution of aerospace composite materials. In
Advanced Composites in Aerospace Engineering Applications; Springer, 2022; pp. 367–385.
29.
Rahman, M.; Shaw, J.; Roesel, M.; William, B.; Willis, J.; Salekeen, S.; Ahmed, M. Finite Element Analysis of
Silica Aerogel to Be Used in High Temperature Insulation Tiles for next Generation Space Tiles 2015.
30. Burr, K. Reuseable lightweight modular multi-layer insulation for space shuttle. Technical report, 1973.
31.
Barber, J. Cryogenic insulation technology review for the space shuttle. In Proceedings of the SPACE
TRANSPORTATION SYSTEM TECHNOL. SYMP., VOL. 5 JUL. 1970, 1970.
32.
Vaz, R.F.; Garfias, A.; Albaladejo, V.; Sanchez, J.; Cano, I.G. A Review of Advances in Cold Spray Additive
Manufacturing. Coatings 2023,13, 267.
33.
Tanzilli, R.A. Development of an External Ceramic Insula-tion for the Space Shuttle Orbiter. NASA
CR-112257,-National Aeronautics and Space Administration 1973.
34. Silver, F. Biomaterials, Medical Devices and Tissue Engineering: An Integrated Approach: An Integrated Approach;
Springer Science & Business Media, 1993.
35.
Florence, D.; Gorsuch, P.; Tanzilli, R. Reusable external insulation TPS for the space shuttle. In Proceedings
of the NASA. MANNED SPACECRAFT CENTER NASA SPACE SHUTTLE TECHNOL. CONF., VOL. 2
APR. 1971, 1971.
36.
Forsberg, K. Description of the manufacturing challenges in producing the high-temperature reusable
surface insulation for the thermal protection system of the Space Shuttle. In Proceedings of the Congres
International Aeronautique, 1979, number AAAF PAPER NT 79-42.
37.
Fleck, R.; Lehman, J. Mechanical Attachment of Reusable Surface Insulation to Space Shuttle Primary
Structure. In Proceedings of the NASA. Ames Res. Center Symp. on Reusable Surface Insulation for Space
Shuttle, Vol. 3, 1973.
38.
Ganpatye, A.; Kinra, V. Fracture toughness of space shuttle external tank insulation foam. In Proceedings of
the 47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference 14th
AIAA/ASME/AHS Adaptive Structures Conference 7th, 2006, p. 2020.
39.
Brazel, J.; Tye, R. Thermal characterization of reusable external insulation for the space shuttle. Technical
report, 1972.
Preprints.org (www.preprints.org) | NOT PEER-REVIEWED | Posted: 22 April 2025 doi:10.20944/preprints202402.0382.v2
31 of 31
40.
McWhorter, B.; Ewing, M.; Albrechtsen, K.; Noble, T.; Longaker, M. Real-time measurements of aft
dome insulation erosion on space shuttle reusable solid rocket motor. In Proceedings of the 40th
AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 2004, p. 3896.
41. Finckenor, M.M. Materials for Spacecraft.
42.
Sharma, V.; Garg, A. Numerical Investigation of Effects of Compound Angle and Length to Diameter Ratio
on Adiabatic Film Cooling Effectiveness. CoRR 2014,abs/1405.0560.
43.
Chandrashekar, P.; Garg, A. Vertex-centroid finite volume scheme on tetrahedral grids for conservation laws.
Computers & Mathematics with Applications 2013,65, 58–74.
44. Snapp, C. Evaluation of Space Shuttle Tile Subnominal Bonds 2006.
45.
Delfini, A.; Santoni, F.; Bisegna, F.; Piergentili, F.; Pastore, R.; Vricella, A.; Albano, M.; Familiari, G.;
Battaglione, E.; Matassa, R.; et al. Evaluation of atomic oxygen effects on nano-coated carbon-carbon
structures for re-entry applications. Acta Astronautica 2019,161, 276–282.
46.
Delfini, A.; Pastore, R.; Santoni, F.; Piergentili, F.; Albano, M.; Alifanov, O.; Budnik, S.; Morzhukhina, A.;
Nenarokomov, A.; Titov, D.; et al. Thermal analysis of advanced plate structures based on ceramic coating on
carbon/carbon substrates for aerospace Re-Entry Re-Useable systems. Acta Astronautica 2021,183, 153–161.
47.
Orbiter Thermal Protection System. NASA’s Kennedy Space Center Public Affairs Office, 2006. Archived
from the original (PDF) on June 10, 2011. Retrieved June 7, 2011.
48.
NASA. Advanced Flexible Reusable Surface Insulation Blankets. April 7, 2002, 2001. Archived from the
original on February 10, 2001. Retrieved June 7, 2011.
49. Lardas, M. Space Shuttle Launch System 1972–2004; Bloomsbury Publishing, 2012.
50.
NASA. STS-41D Press Kit. August 1984. Archived from the original (PDF) on March 15, 2013. Retrieved
July 12, 2013.
51.
Garg, A.; Mishra, H.; Pattanayek, S.K. Scaling Laws for Optimized Power-Law Fluid Flow in Self-Similar
Tree-like Branching Networks. Journal of Applied Physics 2024,135.
52.
Garg, A. Scaling laws for optimal power-law fluid flow within converging-diverging dendritic networks of
tubes and rectangular channels. Physics of Fluids 2024,36, 073116, [https://pubs.aip.org/aip/pof/article-
pdf/doi/10.1063/5.0217953/20076362/073116_1_5.0217953.pdf].https://doi.org/10.1063/5.0217953.
53.
Fontana, J.V.; Garg, A. Optimal power-law fluid flow in tree-like branching networks with self-similar and
uniform roughness models. Journal of Applied Physics 2025,137.
54.
Garg, A.; Bergemann, N.; Smith, B.; Heil, M.; Juel, A. Fluidisation of yield stress fluids under vibration.
Journal of Non-Newtonian Fluid Mechanics 2021,294, 104595.
55.
Garg, A. Fluidisation of yield stress materials under vibration. PhD thesis, The University of Manchester 2022,
pp. 1–175.
56.
Pataranutaporn, P.; Sumini, V.; Ekblaw, A.; Yashar, M.; Häuplik-Meusburger, S.; Testa, S.; Obrist, M.;
Donoviel, D.; Paradiso, J.; Maes, P. SpaceCHI: Designing human-computer interaction systems for space
exploration. In Proceedings of the Extended Abstracts of the 2021 CHI Conference on Human Factors in
Computing Systems, 2021, pp. 1–6.
57.
Pataranutaporn, P.; Sumini, V.; Yashar, M.; Testa, S.; Obrist, M.; Davidoff, S.; Paul, A.M.; Donoviel, D.; Wu, J.;
Fish, S.A.; et al. SpaceCHI 2.0: Advancing Human-Computer Interaction Systems for Space Exploration. In
Proceedings of the CHI Conference on Human Factors in Computing Systems Extended Abstracts, 2022, pp.
1–7.
58.
Coblentz, M.; Evans, J.D.; Kothe, C.I.; Mak, T.; Valeron, N.R.; Chwalek, P.; Wejendorp, K.; Garg, S.; Pless, L.;
Mak, S.; et al. Food Fermentation in Space Is Possible, Distinctive, and Beneficial. bioRxiv 2024, pp. 2024–02.
59.
Sun, Y.; Kuang, Y.; Zuo, Z. The emerging role of macrophages in immune system dysfunction under real
and simulated microgravity conditions. International Journal of Molecular Sciences 2021,22, 2333.
60.
Kumar, R.K.; Singh, N.K.; Balakrishnan, S.; Parker, C.W.; Raman, K.; Venkateswaran, K. Metabolic modeling
of the International Space Station microbiome reveals key microbial interactions. Microbiome 2022,10, 102.
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