1 Introduction

Aerospace systems operate across a sequence of mission stages, including launch, on-orbit service, long-duration deep-space exploration, re-entry and recovery, and crewed operations. Although each stage involves distinct loading conditions and environmental exposures, they pose a common requirement for materials: the material system must remain functional and reliable under shock [1, 2], vibration [3], vacuum [4], atomic oxygen [5], large temperature variations [6, 7], accumulated radiation damage [8], and long-term thermomechanical interactions. These challenges are becoming increasingly prominent in current aerospace developments, such as deep-space exploration missions exemplified by the NASA Artemis program and large-scale commercial satellite constellations represented by SpaceX Starlink. In this context, metals and fiber-reinforced composites remain essential because they provide high load-bearing capacity and structural stability. In addition, as aerospace systems move toward large deployable components, long-duration autonomous operation, intelligent sensing, and closer coupling between hardware and humans, the key issue is no longer how a material performs under a single dominant load, but how it maintains performance when several extreme factors act together over time [9]. Elastomers, hydrogels, aerogels, shape-memory polymers, and related composites generally combine low modulus [10, 11], large deformation [12, 13], high hysteresis [14, 15], and tunable response to external stimuli [16−20]. These characteristics make them useful in aerospace engineering, such as lightweight elements that integrate structure, actuation, sensing, and protection [9, 21].

At the launch stage, the most direct uses of soft materials are shock reduction, vibration control, and sealing. Ignition, stage separation, and pyrotechnic events generate transient impact loads. In contrast, broadband vibration—typically comprising sinusoidal and random components—arises from engine thrust oscillations, engine-induced noise, and aerodynamic excitation. Under these combined dynamic disturbances, mechanically disturbed interfaces must still maintain effective sealing. Compared with rigid connections, soft materials can dissipate energy through viscoelastic damping and localized chain scission, and reduce load transfer across interfaces, which is advantageous for lightweight vibration-control design. Sealing, moreover, is not determined only by contact geometry. It is also governed by pressure-driven transport processes, including diffusion and advection. Garafolo and Daniels [22] showed that leakage in elastomeric space seals cannot be described adequately by diffusion alone, and that compressibility together with pressure-dependent permeability must be considered. This example illustrates that the mechanical and transport behavior of soft materials can be engineered for specific functions.

During on-orbit service, the engineering focus shifts from meeting launch-stage mechanical requirements to achieving reliable operation in space while enabling large functional structures. Spacecraft must deploy large components after launch from a compact stowed configuration, but they must also withstand vacuum, atomic oxygen exposure, and repeated thermal cycling. This combination of design and environmental requirements has made deployable and inflatable structures increasingly important [23]. Soft materials provide a practical basis for these architectures. Shape-memory polymers and their composites can be folded into compact forms, triggered to recover their programmed shapes, and adjusted in stiffness after deployment, which makes them attractive for antennas, solar arrays, booms, and other deployable systems. As summarized by Yadav et al. [24], their appeal lies in large recoverable strain, low structural mass, and relatively low actuation energy. Aerogels provide another important route at this stage. Their nanoporous structures suppress solid, gas-phase, and radiative heat transfer, giving them distinct advantages for thermal management under coupled thermal and mechanical conditions [25].

For long-duration deep-space missions, the problem extends beyond environmental resistance to long-term autonomous functionality. Continuous exposure to cosmic radiation, high-energy particle events, long mission durations, and restricted maintenance opportunities means that materials must do more than simply resist degradation. They should also tolerate damage, indicate performance changes, and ideally recover at least part of their functionality. Soft materials are especially relevant here because their molecular networks and internal architectures are highly tunable, making it easier to combine multiple functions such as shielding, self-repair, and stimulus response within one material platform. Pernigoni et al. [26] demonstrated that self-healing polymer candidates can recover from puncture in spacesuit-related scenarios, but also found that radiation exposure weakens healing performance. This finding highlights an important point: deep-space soft materials should be judged by whether they retain functionality after prolonged exposure to coupled thermal, mechanical, and radiation-related damage. Future aerospace materials should move beyond passive endurance toward active response and structural-functional integration [9].

During re-entry and recovery, thermal protection remains the primary concern. In addition to thermal insulation, materials are increasingly expected to provide damage tolerance and mechanical adaptability. Conventional rigid thermal-protection materials remain important for high-temperature applications [27, 28], but they are less effective when complex surfaces, thermal shock, or local damage must be accommodated. Soft or compliant porous thermal materials, especially aerogel-based systems, offer a different design strategy. Their high porosity and multiscale resistance to heat transfer enable extremely low thermal conductivity, while also allowing greater flexibility in structural design [29]. Jin et al. [25] describe aerogels as outstanding thermal-insulation materials for aerospace applications. More importantly, their significance lies not only in insulation itself, but in the possibility of building thermal-protection systems that are more tunable, damage-tolerant, and functionally integrated.

In crewed aerospace applications, soft materials play an even broader role because they operate directly at the interface between the human body, equipment, and the surrounding environment. As long-duration habitation and deep-space missions advance, materials must satisfy requirements for conformability, biocompatibility, continuous monitoring, and local protection [30, 31]. For this reason, flexible sensors and wearable electronics are becoming increasingly important in human-support systems. Yang et al. [32] reported a flexible aerogel sensor that combines pressure sensing, thermal insulation, and stable operation under extreme temperatures, and suggested its relevance to spacesuits and future habitats. At the same time, the properties and functions of soft materials in space must be reconsidered from a more fundamental physical perspective. Ben Amar et al. [33] showed that microgravity changes the balance among geometric nonlinearity, capillarity, and gravitational effects, which means that the behavior of soft matter in space cannot be monitored simply from ground-based conditions.

Overall, the role of soft materials in aerospace engineering is changing from passive use in components such as seals, damping pads, and insulating fillers to more integrated functions related to structural reconfiguration, thermal management, environmental adaptation, flexible sensing, and human support. As shown in Figure 1, this review is organized around the full aerospace mission lifecycle, with particular emphasis on impact and vibration mitigation, sealing, deployable structures, thermal management, radiation protection, flexible electronics, and multifunctional integration. To complement this mission-based overview, Table 1 summarizes representative soft-material platforms for each functional category, together with their key performance, aerospace application scenarios, and main limitations or validation needs. These topics will be reviewed and discussed in the following sections.

Figure 1 Representative soft material classes and their major application scenarios in aerospace engineering

2 Impact Resistance and Vibration Mitigation

In aerospace engineering, launch shock, pyroshock, broadband vibration, long-term microvibration, and extreme thermal cycling act on structures and payloads over very different time and energy scales. As a result, it is essential to simultaneously address stiffness, impact protection, cyclic durability, thermal tolerance, and low mass within an integrated material-structure system. As shown in Figure 2A, Deng et al. [34] showed on a satellite imaging platform that rubber shock absorbers can reduce microvibration transmitted from the flywheel and improve imaging performance. Both simulation and experiment indicated an improvement of about 10% in modulation transfer function, highlighting the practical value of viscoelastic soft isolators for on-orbit vibration control [34, 35]. At the same time, isolators based purely on soft rubber remain constrained by a familiar contradiction: low stiffness is favorable for high-frequency isolation, but it also shifts resonance into the low-frequency range and increases the risk of excessive deformation and fracture under severe launch vibration. Han et al. [36] highlighted this limitation and proposed a pseudoelastic hybrid isolator specifically to improve attenuation across both low-frequency vibration and high-frequency pyroshock conditions, underscoring that the core requirement is not only attenuation, but attenuation without loss of structural stability under harsh loading.

Figure 2 Soft materials and their composites and structures for impact resistance and vibration mitigation. (A) Rubber shock absorbers for flywheel-induced microvibration in satellite imaging systems. Reproduced with permission from Ref. [34]. Copyright 2016, The Author(s). (B) Elastomer-encapsulated polymer fluids for egg-drop impact protection. Reproduced with permission from Ref. [37]. Copyright 2021, The Author(s). (C) Armored polymer–fluid gels with high loss factors over a broad temperature range. Reproduced with permission from Ref. [38]. Copyright 2025, The Author(s). (D) Molecular-friction hydrogels with rapid damping recovery. Reproduced with permission from Ref. [39]. Copyright 2024, The Author(s). (E) Thermally stiffening hydrogels with rapid recovery capability. Reproduced with permission from Ref. [40]. Copyright 2025, The Author(s). (F) Gradient double-twisted Bouligand structures for high impact resistance. Reproduced with permission from Ref. [41]. Copyright 2025, The Author(s)

At the material level, a central limitation of conventional viscoelastic polymers lies in the trade-off between damping capacity and modulus, together with their relatively narrow effective frequency and temperature ranges. Recent studies have therefore focused on material strategies that decouple energy dissipation from stiffness while extending serviceability across broader loading and thermal conditions. Huang et al. [37] showed that elastomers containing confined polymer fluids can dissipate energy through hierarchical relaxation over an exceptionally broad frequency range of 10⁻²−10⁸ Hz while maintaining a nearly stable modulus; in their tests, the loss factor exceeded 0.5, the impact force was reduced by as much as 85%, and vibration attenuation reached 90%, demonstrating that soft damping media can be designed for both transient impact and sustained excitation (Figure 2B). Chen et al. [38] extended this idea through armored polymer-fluid gels, where a stiffened outer layer and dissipative interior jointly mitigated the damping-modulus trade-off over a wide service temperature range from −45℃−135℃; under these conditions, rebound was reduced by more than 98%, and vibrational force was lowered by as much as 72% under low-temperature loading, which is especially relevant to aerospace environments with large thermal excursions (Figure 2C). Hydrogels add another design dimension because they introduce not only dissipation, but repeated and adaptive mechanical response. Xu et al. [39] showed that molecular-friction hydrogels can restore damping within seconds after deformation, thereby overcoming the slow recovery associated with sacrificial-bond systems (Figure 2D), while Li et al. [40] developed thermal-stiffening hydrogels that can switch rapidly from compliant to load-bearing states and then recover quickly enough to support repeated impact resistance (Figure 2E). These studies indicate that soft impact-resistant materials are moving from passive dissipative media toward programmable systems in which damping, stiffness, temperature response, and recoverability are designed simultaneously.

Structural approaches provide a further route to impact and vibration resistance, with protective performance generated through hierarchy, topology, and wave regulation rather than through intrinsic material damping alone. Wen et al. [41] showed that a gradient double-twisted Bouligand architecture composed of stiff Polylactic Acid (PLA) and soft Thermoplastic Polyurethane (TPU) improves impact resistance over loading conditions ranging from quasi-static to ballistic, illustrating how bioinspired hierarchical design can broaden protective performance across different strain-rate regimes (Figure 2F). Reviews of low-frequency acoustic metamaterials and porous materials further show that tunable resonance, negative-Poisson-ratio deformation, and multiscale wave attenuation provide additional routes for broadband vibration suppression and impact energy redistribution in lightweight systems [42, 43]. Feng and Li [44] argued that damping systems should be evaluated within an integrated material-structure-performance framework, because high damping alone cannot ensure effective vibration suppression without adequate stiffness and suitable deformation modes; in this context, self-healing constituents enable repeatable damping structures by restoring dissipation after damage. The same trend is now extending to design methodology, where data- and mathematics-driven optimization is being used to co-design metamaterial topology and target functions for lightweight energy absorption and vibration-control behavior [45]. Overall, the most promising direction is to integrate soft-material dissipation, hierarchical structural design, reusable or self-healing functionality, and inverse design into aerospace-specific systems capable of withstanding both instantaneous impact and sustained vibration under realistic mission environments.

3 Sealing and Leakage Control

Sealing and leakage control are indispensable in aerospace engineering because loss of sealing integrity can compromise pressure containment, medium isolation, and environmental protection even when a seal remains under nominal compression. For soft sealing systems, leakage is not a simple consequence of insufficient preload or geometric mismatch; rather, it arises from the coupled evolution of interfacial contact, viscoelastic stress relaxation, and flow through non-contact channels across multiple length and time scales. This point has been clarified in rough-surface contact mechanics, where sealing performance is governed by the real contact condition and the connectivity of non-contact leakage paths rather than by nominal contact area alone [46]. Viscoelastic contact analyses showed that time-dependent loading alters interfacial separation, real contact area, and dissipative behavior, so that leakage pathways become dependent on loading history under cyclic or sustained service (Figure 3A) [47, 48]. Huang et al. [49] developed a predictive leakage model for irradiated ethylene propylene diene monomer O-rings by coupling macroscopic simulations of O-ring deformation with mesoscopic simulations of interfacial leakage. Their results showed that leak rate cannot be predicted from irradiation-induced material changes alone, because surface roughness, compression ratio, and pressure differential also govern the morphology and connectivity of interfacial flow channels (Figure 3B). In addition, Li et al. [50] reported a result for O-ring seals under high-temperature and high-pressure conditions: although elevated temperature may temporarily increase contact stress and improve sealing in the short term, prolonged exposure accelerates stress relaxation, extrusion, and leakage growth. This finding indicates that the key challenge for O-ring sealing reliability lies not in short-term sealing enhancement, but in the long-term degradation of sealing performance.

Figure 3 Mechanics of soft-material sealing. (A) Interaction between a nominally flat, randomly rough rigid surface and a substrate described by a standard viscoelastic model. Reproduced with permission from Ref. [47]. Copyright 2021, Elsevier. (B) Schematic illustration of the leakage mechanism of an O-ring. Reproduced with permission from Ref. [49]. Copyright 2023, The Author(s). (C) Characteristic-length-controlled cavitation and fracture in soft materials. Reproduced with permission from Ref. [56]. Copyright 2026, Springer Nature. (D) Schematic illustration of particle diffusion through an undeformed hydrogel and hydrogels under uniaxial tension. Reproduced with permission from Ref. [57]. Copyright 2024, Elsevier

The sealing problem becomes more complex when the sealed medium is chemically reactive or highly diffusive. In hydrogen environments, Zhou et al. [51] showed that gas transport in rubber follows a solution-diffusion mechanism involving sorption, diffusion, and desorption, with hydrogen permeability governed by pressure, temperature, filler characteristics, crosslink density, and polymer polarity. In high-pressure hydrogen environments, gas transport is closely linked to the permanent deformation of rubber seals. Zheng et al. [52] showed that swelling, modulus degradation, cavitation and fracture by rapid gas decompression [53−56] (Figure 3C), and extrusion-related cracking may develop concurrently, indicating that seal failure should be understood as a coupled mechanics-transport problem rather than as a simple consequence of geometric mismatch. A broader mechano-transport perspective is provided by Liu et al. [57], who showed that diffusivity in deformed polymer networks is controlled by two dimensionless parameters: the ratio of particle diameter to mesh size, and the ratio of current polymer chain length to its initial length. Their results indicate that transport in soft polymers is deformation-dependent, so diffusivity should be incorporated into sealing analysis as a mechanically coupled parameter (Figure 3D). The same logic extends to aging caused by radiation. Chain scission, crosslinking, and diffusion-limited oxidation evolve concurrently over long service periods, progressively changing both stress-retention capability and barrier performance [58, 59]. For silicone-based sealing materials, long-term stability remains a challenge, because thermal-oxidative aging, including oxidative crosslinking and scission of molecular chains, progressively degrades network integrity unless they are mitigated through formulation design, interfacial compatibility, and network stabilization [60].

Accelerated testing and life prediction remain difficult because sealing reliability cannot be inferred from a single test result or a material property. Jung [61] showed that the gas uptake, solubility, and diffusivity obtained from gravimetric, volumetric, manometric, and gas-chromatographic methods are generally consistent, while the methods differ in resolution, stability, expanded uncertainty, sensitivity to temperature and pressure, and practical applicability; in this sense, the main issue is how measurement route and test condition affect the reliability and usability of those data in leakage evaluation. A similar point appears in radiation-induced degradation. Battini et al. [62] showed that the safe service of gate-valve O-rings exposed to radiation cannot be defined by any single radiation-sensitive material property, but depends jointly on squeeze degree, service time, storage time, and the contact pressure required to preserve sealing; accordingly, their study yielded a life-prediction map rather than a single end-point criterion. In addition, Mahankar and Dhoble [63] showed that hydraulic seal failure under elevated temperature arises from the interaction of swelling, oxidation, loss of additives, compression set, friction, and wear, while Basuli et al. [64] and Patel et al. [65] similarly argued that proton exchange membrane (PEM) fuel-cell gaskets and oil-and-gas elastomer assemblies cannot be evaluated from bulk material tests alone, because chemical compatibility, stress relaxation, extrusion gaps, thermal cycling, and assembly conditions remain strongly coupled at the component scale. Overall, future aerospace sealing research needs predictive frameworks that relate leakage directly to coupled contact mechanics, transport behavior, aging under environmental exposure, and accelerated test conditions, so that service life can be estimated from the evolution of sealing function rather than from isolated material-property changes alone.

4 Intelligent Actuation and Flexible Deployable Structures

In aerospace deployable systems, soft materials offer the potential to integrate compliance, actuation, and functional adaptation directly into the structure, thereby reducing reliance on complex mechanical subsystems. For such systems, compact stowage and reliable deployment are only the initial requirements; equal attention must also be given to post-deployment stiffness, recovery force, geometric accuracy, and stability under the space environment. Wang et al. [23] classified space deployable structures into pantographic (Figure 4A) [66], elastically deployed (Figure 4B) [67], and inflatable systems (Figure 4C) [68], and showed that the significance of smart materials lies in their ability to reduce structural complexity while improving controllability, environmental adaptability, and deployment precision. This requirement is particularly evident in membrane and gossamer structures, where reflector antennas, booms, solar arrays, and inflatable habitats all benefit from high packaging efficiency and low mass, yet remain constrained by wrinkling, shape control, vibration, and deployment reliability [68]. In this context, material-structure coordination remains a critical issue in advanced deployable space systems [69].

Figure 4 Intelligent actuation and flexible deployable structures. (A) A deployed circular solar array. Reproduced with permission from Ref. [66]. Copyright 2022, The Author(s). (B) The GOSSAMER-1 System, four sail segments deployed in a crossed boom configuration. Reproduced with permission from Ref. [67]. Copyright 2014, Springer Nature. (C) Deployed inflatable antenna in space. Image credit: NASA [68]. (D) 4D-printed active sandwich structures in folded and initial configurations. Reproduced with permission from Ref. [76]. Copyright 2020, IOP Publishing Ltd. (E) Metamaterial cells with different configurations and a fabricated device. Reproduced with permission from Ref. [77]. Copyright 2025, The Author(s). (F) The pixel mechanical metamaterials with multifunctional and reprogrammable properties developed by arraying uncoupled constraint-based independent modular mechanical pixels. Reproduced with permission from Ref. [78]. Copyright 2025, The Author(s)

Shape-memory polymers (SMPs) and their composites are among the most extensively studied soft-material systems for intelligent deployment in aerospace. Xia et al. [70] noted that the shape-memory effect in polymers can be interpreted through complementary thermoviscoelastic and phase-transition frameworks, while composite design extends actuation beyond direct heating to electricity, light, magnetism, water, and other external stimuli. Yadav et al. [24] showed that, relative to shape-memory alloys, SMPs generally offer higher recoverable strain, lower density, easier processing, and lower actuation energy, which accounts for their continued use in antennas, hinges, booms, and related deployable elements; however, they also emphasized that vacuum, ultraviolet irradiation, and thermal cycling remain important constraints on long-term service performance. A more application-oriented perspective was provided by Liu et al. [71], who reviewed hinges, foldable and coilable booms, deployable panels, reflector antennas, and morphing wings made of shape memory polymer composites (SMPCs), and showed that the engineering significance of SMPCs lies in their ability to balance low structural mass, recovery force, and deployment shock within a single deployable system. Dao et al. [72] designed carbon-fabric-reinforced SMPC hinges for space deployable structures and found that carbon-epoxy reinforcement improved both stiffness and shape recovery, but repeated folding and deployment also led to progressive damage and longer recovery times, indicating that cyclic durability is a central requirement for practical aerospace use. More broadly, the key challenge lies in achieving stable and controllable actuation under coupled thermal, mechanical, and environmental conditions, while preserving recovery force, dimensional stability, and repeatable deployment performance [73].

A significant development in this field is the increasing integration of actuation, structural design, and manufacturing. Programmable deployment does not arise from responsive materials alone, but from spatially organized heterogeneity, such as gradients, multilayers, patterned stiffness, and active fillers, through which local deformation can be transformed into controlled global shape change [74]. Additive manufacturing enables material response to be encoded into geometry and spatial arrangement [75]. This strategy is evident in 4D-printed deployable structures. As shown in Figure 4D, Xin et al. [76] designed origami-inspired honeycomb sandwich structures combining shape-memory actuation with sandwich stiffening, so that thin responsive sheets can achieve both large shape transformation and sufficient stiffness after deployment for antenna-like applications. The same design logic has also extended from one-time self-deployment to reprogrammable multifunctionality. Yang et al. [77] developed gradient metamaterials based on thermo-, photo-, electro-, and magneto-responsive SMP nanocomposites, showing that multi-material 4D printing can coordinate shape change and mechanical response within a single structure (Figure 4E). Xin et al. [78] further proposed modular 4D pixel mechanical metamaterials, in which properties such as multistability and compression-torsion coupling are determined by reconfigurable unit design rather than fixed once at fabrication (Figure 4F). Much of the existing work has focused on actuation design and functional expansion under relatively conventional conditions. In aerospace deployable systems, however, structural performance must be maintained after deployment under extreme environments such as large thermal excursions and high-temperature exposure. This requirement brings non-actuating soft materials into the design problem as well. Flexible aerogels and multifunctional polymer nanocomposites, for example, can provide compliant thermal-protection layers, deformable interfaces, and additional functional integration, thereby extending the material and structural design space of deployable soft systems [79, 80].

5 Thermal Insulation and Management

Among the aerospace applications of soft materials, thermal insulation and management are particularly important, as they address the severe thermal conditions encountered in modern space missions—from crewed lunar landings and deep space exploration to hypersonic flight and large inflatable space stations. These missions require protection against extreme cyclic thermal environments spanning from −270℃ in deep space to over 1200℃ during hypersonic re-entry, together with stringent requirements for lightweight design, geometric conformability, and low energy consumption. Conventional rigid solutions, including bulk ceramic heat shields, metallic thermal control structures, and traditional multi-layer insulation (MLI), are increasingly constrained by trade-offs among thermal efficiency, mechanical flexibility, and long-term durability in space environments. In this context, nanostructured soft materials provide new opportunities for aerospace thermal management.

Carbon nanofiber aerogels (CNFAs) are promising candidates for high-performance thermal insulation through rational nanostructure design, extending the use of soft materials toward more demanding thermal-protection scenarios. Constructed from three-dimensional interconnected one-dimensional nanofiber networks with porosities exceeding 99% and pore sizes smaller than the mean free path of air molecules, CNFAs can simultaneously suppress gaseous convection, solid heat conduction, and high-temperature infrared radiative transfer across a wide temperature range. Recent advances in electrospinning fabrication, biosynthesis, and interface engineering have substantially improved the historical fragility and irreversible structural collapse of conventional carbon aerogels: state-of-the-art CNFAs achieve room-temperature thermal conductivity as low as 0.02 W m⁻¹ K⁻¹ [81], exceptional thermomechanical stability spanning from −196℃ to 1000℃ [81, 82], an extremely fast structure recovery speed of 860 mm s⁻¹ alongside high compressive strength (Figure 5A) [83], and fatigue resistance reaching up to millions of compression cycles without plastic deformation (Figure 5B) [84]. An ultralight carbon nanofiber aerogel can stably stand on a dandelion and support heavy weights thousands of times its own mass [85]. For aerospace applications, these CNFAs offer an ultralight solution with potential relevance to hypersonic vehicle leading edges, lunar lander cryogenic systems, and micro-satellite thermal control units, while potentially reducing launch weight and active thermal-control loads.

Figure 5 Soft materials for thermal insulation and thermal management. (A) Schematic illustration of the general synthetic process for carbon nanofiber aerogels using one-dimensional nanowires as templates. Reproduced with permission from Ref. [83]. Copyright 2019, John Wiley and Sons. (B) Hierarchical microstructure of carbon nanofiber aerogels. Reproduced with permission from Ref. [84]. Copyright 2020, John Wiley and Sons. (C) Microstructure of dual-gradient nanofiber aerogels and their applications in spacesuit health monitoring and thermal insulation under extreme conditions. Reproduced with permission from Ref. [90]. Copyright 2026, The Author(s). (D) Glass–polymer hybrid metamaterial with randomly distributed silica microsphere inclusions for scalable radiative cooling. Reproduced with permission from Ref. [92]. Copyright 2017, The American Association for the Advancement of Science. (E) Scanning electron microscopy images of various PMMA films, together with their reflection spectra in the solar wavelength range and infrared emissivity spectra. Reproduced with permission from Ref. [94]. Copyright 2021, The Author(s)

Flexible aerogel insulation materials have also advanced rapidly, particularly for next-generation spacesuits. These materials use the inherent conformability of soft materials to address the geometric limitations of rigid insulation and thereby broaden the design space of human spaceflight systems. Traditional spacesuit MLI suffers from excessive thickness, weight, and poor conformability to joint regions, which severely restricts astronaut mobility. While pristine silica aerogels feature extremely low solid-state thermal conductivity, their brittleness and powder shedding have long hindered aerospace deployment. The detached powder acts as a contaminant, adhering to optical surfaces, seals, and electronic components, ultimately causing payload failure. Recent innovations in organic-inorganic hybridization have substantially improved these limitations. Pioneering flexible polyimide aerogels from NASA withstand temperatures up to 400℃ with high tensile strength [86]. Polyimide-silica (PI/SiO₂) hybrid aerogels now achieve ultra-low densities of 0.061 g cm^–3 and thermal conductivities of 0.0216 W m^–1 K^–1, while demonstrating no fracture even under 80% compressive strain [87]. Moreover, they support heavy weights exceeding 2,999 times their own mass without structural collapse [88]. Under simulated space environments, they maintain stable insulation despite high-vacuum outgassing, high-energy proton/electron irradiation, and extreme thermal cycling [87]. Furthermore, double-network PI/SiO₂ aerogel formulations mitigate cryogenic brittleness and exhibit a 60% lower thermal conductivity than pristine silica at 100% relative humidity [89], which may help reduce thermal-management demands in life-support-related systems. This environmental adaptability is further illustrated by the recently developed dual-gradient polyimide nanofiber/carbon nanotube (PINF@CNTs) aerogels. As demonstrated in Figure 5C, such advanced PI-based aerogels can maintain stable piezoresistive sensing capabilities under cryogenic conditions (−196℃) and provide thermal management on a ~500℃ hot surface, indicating their potential for astronaut health monitoring and thermal protection in spacesuits [90].

Flexible thermal-control coatings and radiative-cooling soft materials constitute another active direction, especially for spacesuits and flexible deployable aerospace structures, where soft materials may enable thermal-management configurations that are less accessible to rigid solutions. In the vacuum of space, thermal radiation is the only viable heat-rejection pathway. Conventional rigid metallic coatings with fixed emissivity cannot readily adapt to cyclic thermal environments or flexible non-planar surfaces. Recent advances in spectral engineering have yielded flexible soft coatings with on-demand thermal regulation: for autonomous thermal control, ESA-backed smart optical solar reflectors (meta-OSRs) utilizing W:VO₂ metasurfaces on space-grade polyimide achieve a high-temperature emissivity of 0.80 and a contrast of 0.33 near a transition temperature of 30℃, saving up to 50% of spacecraft heating power [91]. For passive daytime radiative cooling, scalable glass-polymer hybrid metamaterials [92] and transparent fluorinated polyimide (FPI) foils embedding SiO₂ microspheres [93] represent important recent advances. Specifically, the FPI/SiO₂ foils achieve ultralow solar absorptivity (0.07) and high infrared emissivity (0.94) within the atmospheric window [93]. Meanwhile, the scalable roll-to-roll manufactured glass-polymer hybrid metamaterials deliver a noon-time cooling power of 93 W m^–2 under direct sunlight (Figure 5D) [92]. Similarly, hierarchically porous structural polymers, such as rationally designed PMMA films, have been developed for efficient all-day passive radiative cooling. As illustrated in Figure 5E, such porous polymer films exhibit a bright white appearance for high solar reflectance and can deliver stable, continuous sub-ambient cooling performance during midday [94]. These material systems may also offer weight advantages relative to rigid structures.

6 Radiation, EMI and Atomic-oxygen Protection

Aerospace materials are exposed to coupled space stressors, including ionizing radiation, electromagnetic irradiation, atomic oxygen (AO), vacuum, ultraviolet exposure, and thermal cycling. These conditions accelerate degradation and impose stringent demands on mass efficiency, mechanical compliance, and durability [95, 96]. Three hazards are particularly consequential: ionizing radiation beyond Earth's magnetic shielding [96], non-ionizing electromagnetic irradiation in highly integrated electronic systems [97], and AO erosion in low-Earth orbit (LEO) and very-low-Earth orbit (VLEO), which progressively degrades exposed polymeric surfaces [98, 99]. Recent advances show that soft frameworks can integrate hydrogen-rich networks, conductive nanostructures, and silicon-based hybrid chemistries to deliver radiation attenuation, electromagnetic interference (EMI) shielding, and AO resistance within a unified materials strategy [97−99].

For ionizing-radiation protection, the central design principle in soft materials is to combine hydrogen-rich matrices that moderate incident particles with functional fillers that selectively absorb or attenuate specific radiation components. Recent studies have shown that poly(vinyl alcohol) (PVA)-based gels, owing to their high water content, can effectively dissipate the energy of high-energy charged particles, while boric-acid crosslinking not only stabilizes the polymer network but also enhances engineering relevance for astronaut radiation protection (Figure 6A) [100]. Lambertini and co-workers [101] developed passive shielding models based on poly(vinyl alcohol)/boric acid (PVA/BA) gels for astronaut protection and spacesuit applications beyond LEO, demonstrating the practical value of such flexible gels under solar particle event conditions (Figure 6B). Beyond neat hydrogen-rich systems, current efforts increasingly focus on integrating high-Z constituents, MXenes, boron nitride, and boron-containing motifs to achieve synergistic shielding against gamma rays, neutrons, and mixed-radiation environments [102–105]. For example, porous MXene-BN hydrogels have been shown to provide simultaneous gamma-ray and thermal-neutron shielding while maintaining anti-freezing capability, self-healing behavior, and moisture permeability [103]. Similarly, self-healable polyacrylamide (PAM)/PbO₂/Laponite hydrogels demonstrate that high-Z nanofillers can substantially enhance gamma attenuation, as evidenced by representative γ-ray exposure tests on hydrogel shielding composites (Figure 6C) [102]. Borax-incorporated hydrogel composites further illustrate a rational neutron-shielding strategy based on matrix-mediated moderation coupled with selective capture by functional units [104]. Collectively, these studies suggest that the emphasis in ionizing-radiation protection is moving away from maximizing attenuation coefficients alone and toward constructing lightweight, flexible, and wearable shielding networks more compatible with actual aerospace deployment.

Figure 6 Protection against ionizing radiation, electromagnetic waves, and atomic oxygen. (A) Boric-acid-crosslinked poly(vinyl alcohol) gel as a hydrogen-rich and mechanically compliant platform for astronaut radiation protection. Reproduced with permission from Ref. [100]. Copyright 2024, The Author(s). (B) Integration of a flexible PVA/BA gel into a spacesuit shielding architecture for passive protection beyond low-Earth orbit. Reproduced with permission from Ref. [101]. Copyright 2026, The Author(s). (C) γ-ray exposure tests on radiation shielding hydrogel composite. Reproduced with permission from Ref. [102]. Copyright 2020, The Author(s). (D) Electromagnetic interference shielding mechanism of Aramid nanofiber/MXene-reinforced polyelectrolyte hydrogels. Reproduced with permission from Ref. [109]. Copyright 2025, The Author(s). (E) Scheme showing the electromagnetic interference shielding mechanism of double-network organohydrogels. Reproduced with permission from Ref. [110]. Copyright 2024, The Author(s). (F) RTV silicone-rubber coating on a polyimide substrate as a soft protective strategy against atomic oxygen exposure in low-Earth-orbit environments. Reproduced with permission from Ref. [114]. Copyright 2021, The Author(s). (G) Comparative atomic-oxygen resistance of silsesquioxane-coated polyimide systems under LEO, VLEO, and laboratory exposures. Reproduced with permission from Ref. [113]. Copyright 2025, The Author(s). (H) Schematic illustration of the atomic-oxygen attack mechanism in siloxane coating materials. Reproduced with permission from Ref. [112]. Copyright 2023, The Author(s)

By contrast, protection against non-ionizing radiation is governed primarily by electromagnetic-wave transmission, reflection, absorption, and dissipation, and is thus directly linked to electromagnetic compatibility, stealth, and integrated thermal management in aerospace electronics. Here, the advantages of soft materials lie in their ability to form continuous conductive pathways, porous scattering architectures, and deformable interfaces. MXenes, graphene, aramid nanofibers, and conductive polymers have all been extensively exploited to fabricate high-performance gel-based EMI shielding systems. Liu et al. [106] demonstrated that additive manufacturing of MXene-functionalized conductive polymer hydrogels enables a transition from laboratory-scale formulations to structurally programmable shielding architectures. Zhu et al. [107] further showed that Ti₃C₂T_x MXene composite hydrogels can achieve absorption-dominated EMI shielding, a particularly desirable feature because it mitigates secondary electromagnetic pollution arising from excessive reflection. Likewise, the biomimetic porous MXene-sediment hydrogel reported by Yang et al. [108] leveraged ordered pore channels and highly conductive frameworks to realize exceptionally strong EMI shielding. Importantly, the field is increasingly recognizing that the most valuable systems are not those with the highest nominal shielding effectiveness alone, but those that preferentially dissipate electromagnetic energy through polarization loss, interfacial dissipation, and multiple scattering (Figure 6D) [107, 109]. At the same time, the development of organohydrogels has alleviated the long-standing limitations of conventional hydrogels under low-temperature and dehydration conditions, thereby pushing soft EMI shielding materials closer to realistic use in extreme environments (Figure 6E) [110, 111]. Non-ionizing-radiation protection is therefore evolving toward environmentally resilient, absorption-dominated, and multifunctionally integrated platforms, rather than the simple pursuit of ever-larger dB values.

Among the three protective targets, atomic-oxygen resistance most clearly exposes both the boundaries and the diversification of soft-material strategies. For water-rich or highly hydrophilic network materials, vacuum-induced dehydration combined with persistent AO etching severely constrains their direct use as exposed outer-surface protective layers. Accordingly, the most mature solutions currently rely on silicone rubbers, polysiloxanes, polyhedral oligomeric silsesquioxane (POSS)-containing systems, and silsesquioxane-based hybrids [112–114]. These materials share a common physicochemical advantage: under AO attack, they generate relatively dense SiO_x or SiO₂ passivation layers that suppress continued erosion of the underlying organic matrix [112, 113]. Wang et al. [114] analyzed a two-component room-temperature-vulcanizing (RTV) silicone-rubber coating sprayed on polyimide and showed that AO exposure induced surface cracking and compositional evolution while still confirming the practical potential of silicone-rubber protective layers for spacecraft polymer surfaces (Figure 6F). Goto et al. [113], through comparative exposure of silsesquioxane-coated polyimide films in LEO, VLEO, and laboratory environments, further demonstrated that AO protection in real orbital conditions involves more than surface passivation alone; crack evolution, coating integrity, and coupled environmental degradation all play decisive roles (Figure 6G). More recently, plasma-polymerized siloxane coatings with optimized thickness have been shown to provide improved atomic-oxygen resistance, highlighting the importance of coating-thickness control in balancing barrier performance and structural compliance (Figure 6H) [112]. These findings carry an important implication for the broader soft-material field: if gel-based systems are to be advanced toward exposed space-surface applications, they will likely require silicon-functionalized chemistries, surface barrier layers, or layered composite architectures that separate inner functional roles from outer protective functions.

It is worth noting that the engineering relevance of hydrogel-based radiation shielding should be interpreted with caution. Hydrogen-rich and water-containing polymer networks provide a promising basis for attenuating charged particles and secondary radiation, but most demonstrations have been performed under simplified laboratory irradiation conditions rather than under the coupled environments encountered in space. In service, vacuum exposure may cause dehydration, shrinkage, and loss of conformability. Repeated temperature cycling may also induce freezing, phase separation, cracking, or changes in ion transport and mechanical compliance. Prolonged irradiation may further alter the network through chain scission, additional crosslinking, debonding between fillers and the polymer matrix, and interfacial damage, thereby changing both shielding performance and structural integrity. Thus, current hydrogel shielding systems are better viewed as design concepts for protected, encapsulated, or replaceable architectures, such as spacesuit inner layers, habitat shielding modules, and conformal wearable protection, rather than as materials already qualified for exposed spacecraft surfaces. Future work should move beyond single-factor irradiation tests toward protocols that combine vacuum exposure, thermal cycling, radiation, ultraviolet irradiation, and atomic oxygen, together with accelerated aging and lifetime prediction, to determine whether hydrogel-based systems can retain protective function over mission-relevant timescales.

7 Flexible Sensing and Wearable Systems

Long-duration missions, extravehicular activities, and habitat operation require the continuous acquisition of physiological, mechanical, and environmental information at deformable human–machine interfaces. Flexible sensing and wearable systems used in these settings must therefore maintain conformal contact, electrical continuity, and signal stability when attached to skin, spacesuits, or inflatable structures under stretching, bending, twisting, and repeated motion. In this context, device performance cannot be attributed to the softness of constituent materials alone; it also depends on how structural design redistributes strain, reduces interfacial mismatch, and preserves functional coupling during deformation [115, 116]. Cheng et al. [116] showed that flexible devices are evolving from planar layouts toward bioinspired three-dimensional systems, in which geometry, heterogeneous integration, and structural design are used to maintain conformal contact and expand device functionality. A similar requirement appears in mechanically guided stretchable electronics, where wavy (Figure 7A) [117], island–bridge (Figure 7B) [118], fractal-inspired (Figure 7C) [119], and kirigami layouts allow rigid functional components and compliant substrates to coexist within a deformable system without loss of performance [115]. At the system level, reliable operation further requires the coordinated design of sensing materials, interconnects, encapsulation, power modules, conductive bonding, and multilayer architectures, because repeated deformation can interrupt current pathways and degrade device-level stability if these elements are treated separately [120, 121]. This need for mechanical adaptation is also evident in deployable intracortical probes, where temporary stiffness and post-deployment softening are combined within the same device architecture (Figure 7D). Wang et al. [122] designed a foldable fishbone-like probe on a temperature-responsive shape-memory polymer substrate, reducing the insertion width from about 710 μm in the deployed state to approximately 300 μm in the folded state, and then allowing the branches to recover after implantation. In physiological saline, the substrate modulus at 37℃ decreased from 1.8 GPa initially to 130 MPa after four weeks, while chronic implantation supported stable single-neuron recordings for months, indicating that long-term interface stability in soft electronic systems may require time-dependent mechanical adaptation.

Figure 7 Flexible sensing and stretchable electronics. (A) Wavy structures generated by stretching and compression. Reproduced with permission from Ref. [117]. Copyright 2006, Springer Nature. (B) Optical images of stretchable CMOS inverter arrays, highlighting three different deformation modes: diagonal stretching, twisting, and bending. Reproduced with permission from Ref. [118]. Copyright 2008, National Academy of Sciences. (C) Representative device integrated on a Langendorff-perfused rabbit heart. Reproduced with permission from Ref. [119]. Copyright 2015, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. (D) Rigid probe penetrating a brain phantom, followed by its transition to a soft state after penetration. Reproduced with permission from Ref. [122]. Copyright 2024, National Academy of Sciences. (E) Multifunctional electronic skin for artery-pulse monitoring, swallowing detection, and flexible gripper sensing. Reproduced with permission from Ref. [129]. Copyright 2021, The Author(s). (F) Infrared characterization of a flexible wearable thermoelectric device, showing the hot-side temperature during active cooling and the residual skin-cooling effect after device removal. Reproduced with permission from Ref. [133]. Copyright 2019, The Author(s). (G) Illustration of 3D reaction electrospinning for preparing ceramic nanofibrous aerogels, together with their stretchability and high-temperature resistance. Reproduced with permission from Ref. [136]. Copyright 2022, The Author(s). (H) Scalably fabricated soft transmission lines based on liquid-metal-embedded microstructured fibers, used with time-domain reflectometry to resolve the mode, magnitude, and position of multiple simultaneous pressing and stretching events. Reproduced with permission from Ref. [145]. Copyright 2020, Springer Nature

Reliable adhesion provides another interface-level requirement for wearable electronics and intelligent skins, especially when hydrogel-based sensing or ion-conducting layers must be integrated with skin, textiles, elastomers, metals, or preformed structural substrates. Functional hydrogel coatings show that hydrated soft layers can endow substrates with functions such as biocompatibility, lubrication, antifouling behavior, ionic transport, and sensing, while the substrates provide stiffness, strength, and mechanical support; however, their cyclic durability and long-term stability in wet or harsh environments remain central challenges [123]. At the material level, stitch-bonding offers a chemistry–topology coupled strategy for wet soft adhesion: catechol-functionalized polymer chains infiltrate a hydrogel network, crosslink in situ, and simultaneously bond to diverse surfaces, enabling PAAm hydrogels to adhere to representative substrates with adhesion energies of 200–400 J m⁻² and toughened PAA–PAAm hydrogels to reach approximately 900 J m⁻² [124]. At the structural-mechanics level, debonding resistance can be improved by activating deformation over a larger region ahead of an interfacial crack. Large-scale bridging in 90° peel, achieved by increasing the bending stiffness of the backing layer, increased the maximum peel force per width from 185 to 856 N m⁻¹ for PAAm hydrogels and from 486 to 2054 N m⁻¹ for double-network hydrogels [125]. For reconfigurable or detachable soft interfaces, electroadhesion enabled by ionic double layers provides an additional route: an applied bias drives mobile ions and charged polymer chains in polyelectrolyte hydrogels to form an interfacial electric field and a temporary bridging network, allowing the adhesion to be regulated electrically [126].

On this basis of structural compliance, mechanical adaptation, and robust interfacial bonding, flexible sensing has progressed from isolated transducers toward distributed and multifunctional platforms. Liu et al. [127] provided an early systems-level example by integrating soft electronics, body-motion capture, and haptic feedback into a wireless epidermal human–machine interface, thereby extending wearable electronics from passive monitoring to closed-loop interaction. Luo's technology roadmap similarly framed flexible sensors not as standalone devices but as integrated arrays that must simultaneously deliver sensitivity, selectivity, stretchability, reliability, and scalable connectivity on deforming surfaces [128]. Within this broader direction, Cai et al. [129] developed a multifunctional electronic skin based on patterned metal films, using a single piezoresistive mechanism rather than multiple heterogeneous transduction mechanisms to decouple pressure and temperature sensing through the structural combination of serpentine metal traces and spatially distributed microprotrusions. In that design, the same device could conform to skin for artery-pulse and swallowing monitoring and could also be integrated with a flexible gripper to detect object softness and temperature (Figure 7E). Ji et al. [130] reported a multilayer multisensory electronic skin that combines a protrusion texture, separate pressure and temperature units, and an embedded heater, thereby mimicking the pressure-sensitive, temperature-sensitive, and heat-exchange functions of biological skin within one architecture. In addition, flexible wearable systems are also incorporating functions, including signal conditioning, human–machine interaction, local thermal regulation, and manufacturing-enabled customization. Park et al. [131] showed that a viscoelastic hydrogel-based frequency-selective damper can suppress motion-induced low-frequency noise while preserving target biophysical signals, thereby shifting part of the filtering function from downstream electronics into the soft interface itself. Wen et al. [132] combined self-powered triboelectric textile gloves with machine-learning analysis, so that gesture recognition relied on multichannel signal interpretation under realistic disturbances such as sweat, rather than on simple threshold-based sensing. Hong et al. extended wearable functionality from monitoring to active regulation by showing that flexible thermoelectric devices can provide local cooling in addition to body-related sensing (Figure 7F) [133]. From a manufacturing perspective, Ryan et al. [134] indicated that additive manufacturing and 4D printing provide routes for integrating sensing, self-healing, shape adaptation, and structural customization in scenarios where direct maintenance is limited.

For aerospace electronic skin, multifunctionality must be accompanied by resistance to severe service environments, especially thermal exposure. This requirement has motivated high-temperature flexible electronics as a distinct branch of flexible sensing, in which the sensing layer must remain mechanically compliant while retaining electrical and interfacial stability at temperatures that exceed the working window of most polymeric substrates. In aircraft and spacecraft, such conformal sensing layers are expected to map strain, temperature, pressure, and structural or aerodynamic states over curved airframe components; in external-surface applications, the operating temperature can exceed 500℃, making conventional polymer-supported devices insufficient [135]. Recent studies therefore point to ceramic-fiber membranes, thermally stable conductive networks, and ceramic dielectric layers as candidate building blocks for sensing under these conditions [135]. A representative material-level strategy is to generate compliance through architecture rather than through polymer elasticity. For example, ceramic nanofibrous aerogels prepared by 3D reaction electrospinning use entangled and crimped fiber networks to accommodate deformation, enabling elongation to 100% strain, reversible stretching after exposure to 1300℃, and stability over a temperature window from −196℃ to 1400℃ (Figure 7G) [136]. High-temperature flexible pressure sensors still face coupled limitations associated with thermally stable conductors, ceramic or hybrid substrates, interface integrity, and cyclic structural recovery. Current designs based on fibrous networks, porous frameworks, and spring-like geometries further indicate that future sensing skins should combine transduction, thermal shielding, and deformation tolerance within one integrated architecture [137].

Beyond low-frequency wearable monitoring, aerospace smart skins must also address high-frequency dynamic sensing. Structural health monitoring of aircraft and spacecraft involves vibration, impact, acoustic emission, and guided-wave detection, in which piezoelectric transducers are widely used because they can act as both sensors and actuators in built-in sensor networks [138]. These tasks are substantially different from physiological or human-motion sensing: impact stress waves and Lamb-wave signals commonly operate in the kilohertz to hundreds-of-kilohertz range, as illustrated by flexible piezoelectric Lamb-wave sensors detecting signals at a central frequency of 350 kHz [139]. Recent ultrafast flexible pressure sensors have begun to close this gap. Bonded microstructured piezocapacitive sensors reduced both response and relaxation times to approximately 0.04 ms, enabling vibration detection up to 12.5 kHz, a frequency resolution of 0.2 Hz at 1000 Hz, and a detection limit of 0.007 Pa [140]. Ultrafast piezoresistive flexible pressure sensors based on porous hierarchical structures further captured dynamic stimuli exceeding 20 kHz, with a frequency resolution of 0.1 Hz, a minimum detectable pressure of 1 Pa, and a pressure range from 1 Pa to 1000 kPa [141]. Flexible piezoelectric composite sensors have also been developed for aircraft structural impact monitoring on curved surfaces, with Lamb-wave signals detectable at 75℃ and impact source localization demonstrated on curved structures [142]. These advances show that flexible sensors are no longer restricted to low-frequency wearable signals; however, their bandwidth still only partially overlaps with many aerospace structural-monitoring requirements. For high-frequency smart skins, usable bandwidth, phase fidelity, signal-to-noise ratio, interfacial bonding, and environmental stability under thermal, vacuum, radiation, and cyclic loading must be evaluated together with sensitivity and stretchability.

Complementary material innovations have further broadened the capability of soft platforms. Cheng et al. built self-healable electronic skin from MXene aerogels with a sensitivity of 1799.5 kPa⁻¹, a response time of 11 ms, and stable cycling beyond 25,000 cycles, showing how porous conductive frameworks can improve both electromechanical performance and recoverability [143]. Han et al. [144] addressed the environmental instability of hydrogel wearables by developing ionic hydrogels that remain conductive, adhesive, and self-healable even at −80℃, which is directly relevant to extraterrestrial or cryogenic applications. Yang et al. [32] further showed that conductive composite aerogels based on polyimide fibers can combine superelasticity, thermal insulation, and stable piezoresistive sensing across extreme temperatures, which may support sensing units in spacesuits and inflatable lunar or Martian habitats. At the sensor level, Leber et al. [145] replaced dense point-sensor arrays with soft liquid-metal transmission lines interrogated by time-domain reflectometry, allowing a single distributed probe to resolve the type, magnitude, and position of multiple simultaneous deformation events while markedly reducing interconnect complexity (Figure 7H). Overall, the central requirement for aerospace wearable electronics is the sustained performance of an integrated soft platform under repeated deformation and coupled environmental loading.

8 Multifunctional Integration for Next-generation Aerospace Systems

The evolution of modern aerospace engineering has long been constrained by a foundational architectural paradigm: functional decomposition, where structural load-bearing, sensing, actuation, and power supply are designed as discrete components and assembled post-fabrication. For conventional rigid aerospace systems, this component-wise assembly imposes persistent trade-offs among payload mass efficiency, system reliability, geometric adaptability, and survivability in extreme space environments—trade-offs that have become increasingly difficult to accommodate for next-generation missions, including long-duration deep space exploration, reusable hypersonic flight, large-scale microsatellite constellations, and intelligent extravehicular activity (EVA) systems. Against this backdrop, soft materials are being considered not simply as replacements for rigid bulk materials, but as a materials platform for integrating multiple functions within a single conformable matrix.

At the foundation of this integrated framework lies monolithic sensing-structure integration via piezoresistive carbon nanofiber aerogels (CNFAs), which addresses several limitations of conventional aerospace sensing architectures. Traditional structural health monitoring (SHM) systems rely on discrete, surface-mounted rigid transducers, which require complex wiring, suffer from signal degradation under extreme conditions, and cannot conform readily to curved surfaces. In contrast, the three-dimensional interconnected conductive nanofiber network of aerospace-grade CNFAs endows the material with an intrinsic piezoresistive response while retaining ultralight load-bearing capability. This makes it possible to move from "sensing on the structure" toward "sensing within the structure": state-of-the-art formulations maintain stable, high-sensitivity piezoresistive performance (up to 114.6 kPa⁻¹) across extreme temperature ranges, with negligible drift and > 95% height retention over 10,000 loading cycles [146, 147]. The practical relevance of such monolithic sensing-structure integration is illustrated by the aforementioned PINF@CNTs dual-gradient aerogels, which can deliver stable and repeatable real-time piezoresistive responses for monitoring physiological signals even under extreme cold conditions [90]. For aerospace applications, this monolithic integration offers a possible route to real-time in situ monitoring of deployable antenna deformation, hypersonic thermal-protection-system integrity, and EVA suit kinematics without introducing separate rigid sensing units.

Another important advance is actuation-structure integration via SMPs, which reduces the separation between load-bearing structure and discrete actuation components. Conventional deployable aerospace structures often depend on motors, springs, and other discrete actuation systems that increase structural complexity. As stimulus-responsive soft structural materials, SMPs embed programmable actuation capability directly into the load-bearing matrix: they can be fixed into a compact temporary shape for launch and recover their operational shape through thermal or electrical triggering. Recent aerospace-grade SMP formulations achieve 98%–100% shape recovery fidelity in vacuum environments, together with wide operational temperature windows and good durability [71, 148]. Reported aerospace applications include self-deploying antenna reflectors [71], structural frames [149], and compact deployable solar arrays utilizing elastic origami architectures that achieve a 1000% area expansion ratio in under 40 s [150]. A deployable solar-panel array demonstrates the transition from a compact collapsed configuration to a fully expanded state through embedded actuation, thereby reducing dependence on conventional discrete actuation architectures [150].

To move toward more self-sustaining systems, soft piezoelectric and thermoelectric materials offer an important route for integrated energy conversion and harvesting. Conventional aerospace power systems are dominated by centralized solar arrays and batteries, which can impose substantial mass penalties in long-duration missions. Soft piezoelectric materials can harvest electrical energy from ambient mechanical vibrations, delivering power densities on the order of mW cm⁻³ for SHM sensor nodes [151, 152], while also enabling active aeroelastic control that can reduce structural vibration levels by over 30% [153]. In one such demonstration, flexible macro-fiber piezoelectric patches are embedded directly into the structure of a small civil aircraft for ambient vibrational energy scavenging [151]. Meanwhile, soft thermoelectric materials convert cyclic temperature gradients generated by orbital thermal cycling into usable power, achieving high power factors in flexible modules [154]. This concept has also been examined in realistic aerospace-related settings, such as the installation of a thermoelectric generator near the front left door of an A320 aircraft fuselage to utilize environmental temperature gradients [151]. Because both material classes retain substantial conformability, they provide opportunities for integration with aerospace structures without major changes to the external system envelope, and may therefore support future battery-reduced or battery-assisted systems for microsatellites and smart EVA suits. In aggregate, these integrated soft material systems illustrate a shift away from strictly component-based aerospace design toward multifunctional material architectures. Their significance lies in the possibility of improving mass efficiency, functional integration, and mission adaptability through material-level design.

9 Conclusion and Outlook

This review examines soft materials across the full aerospace mission lifecycle and shows that they are no longer limited to passive roles such as seals, damping pads, or compliant fillers. Instead, they are increasingly being developed as active functional media for impact and vibration mitigation, sealing and leakage control, deployable structures, thermal insulation and management, radiation protection, flexible sensing, and multifunctional integration. Their value lies in the possibility of coupling compliance, transport regulation, actuation, sensing, and environmental adaptation. In this sense, soft materials are emerging as integrated platform enablers for the redesign of aerospace systems.

The main scientific bottlenecks remain unresolved. Aerospace service conditions are intrinsically coupled: high and low temperatures, vacuum, atomic oxygen, radiation, ultraviolet irradiation, humidity loss, and mechanical loading do not act independently, and their interactions often govern the actual aging and failure behavior of soft materials. This implies that future progress will depend on the development of predictive frameworks capable of linking microstructural evolution, deformation, and failure under multiphysical environments. In particular, new mechano-chemical models are required to describe how stress relaxation, network damage, diffusion, oxidation, irradiation-induced chain scission or crosslinking, and interfacial degradation evolve concurrently over long service periods. Such models are especially important for the quantitative prediction of structural integrity and functional stability, both of which are controlled by coupled field effects rather than by isolated material constants.

A related challenge concerns testing and lifetime prediction. Much of the existing literature still relies on simplified laboratory demonstrations, short-duration loading histories, or single-factor environmental tests. Yet the key question for aerospace applications is not whether a material can perform under one selected condition, but whether it can maintain functionality over long durations under realistic mission sequences. This requires accelerated testing methods that go beyond simply increasing temperature or loading frequency. Future methodologies should aim to reconstruct the combined effects of vacuum, radiation, thermal cycling, oxidation, and mechanical perturbation in a controllable manner, so that laboratory experiments can provide reliable guidance for long-term deep-space service. Correspondingly, lifetime prediction should move beyond empirical extrapolation toward a physics-informed, multiscale framework that explicitly links molecular design and mesoscale architecture to macroscopic functional degradation. Without such a framework, it will remain difficult to determine whether excellent laboratory performance can translate into durable aerospace reliability.

The long-standing aerospace demands for conformal attachment, rigid-soft coupling, programmable actuation, vibration attenuation, environmental buffering, and local sensing or regulation are difficult to achieve simultaneously with conventional rigid architectures. Soft materials provide a route toward these combinations because they can store, dissipate, transduce, or redistribute energy while adapting to complex geometries and interfaces. However, this does not imply that soft materials will replace all conventional aerospace materials. For the most severe thermal or ablative environments, especially those associated with the outermost surfaces of high-speed re-entry systems, current soft materials are more realistically viewed as components of layered or hybrid architectures rather than as stand-alone substitutes for ultra-high-temperature structural materials. Their greatest near-term value is likely to lie in compliant insulation layers, deployable thermal interfaces, embedded sensing skins, adaptive coatings, and multifunctional inner protection systems that work together with rigid load-bearing or ablative layers. This layered design logic may prove more important than the search for any single "universal" soft material.

AI-assisted materials discovery and advanced manufacturing are likely to become integral to the development of next-generation soft aerospace systems. Their significance lies in establishing a predictive route from functional requirements to material realization, rather than relying predominantly on empirical trial-and-error. In soft multifunctional systems, performance depends on the coupled effects of chemical composition, microstructural architecture, structural geometry, and environmental response, creating a design space too large to be explored efficiently through experiments alone. AI-assisted materials discovery, inverse design, digital twins, and data-driven multiscale optimization provide complementary approaches to navigating this complexity by linking candidate materials, structural parameters, service conditions, and target functions across scales. Their use is particularly valuable when combined with mechanics-based and multiphysical models. In parallel, 4D printing and multi-material additive manufacturing provide practical routes for realizing such designs. A key future direction is therefore to establish a closed-loop development framework that connects predictive design, multiscale modeling, programmable manufacturing, and mission-relevant validation.