NASA’s use of aerogel—especially in the Stardust Mission—is based on four key material advantages:
    （1）Ultra-Low Density Enables “Soft Capture”

       · Silica aerogel is incredibly light—only a few times denser than air.

       · Cosmic dust particles strike the collector at 6 km/s  (hypervelocity).

       · If they hit metal or glass, they would vaporize.

       · Aerogel acts like a thick, ultra-soft cloud, slowing particles over several centimeters and preserving their original structure.

    （2）Transparency Allows Precise Sample Tracking

       · Silica aerogel is semi-transparent.

       · Scientists can visually follow the “carrot-shaped tracks” left by each particle and extract them accurately using micromanipulation tools.

    （3）Highly Porous Structure Traps Tiny Particles

       · The nanoporous network stops even sub-micron dust without destroying or contaminating it.

    （4） Chemically Clean and Inert

       · Aerogel contains almost no organics, making it ideal for later isotope, mineralogy, and organic chemistry analyses.

2. How NASA’s Stardust Mission Captured Cosmic Dust

    The Stardust process can be summarized in three steps:

    （1）Aerogel Collector Deployment

       · The spacecraft carried a “tennis-racket-shaped” sampler with silica aerogel tiles.

       · One side collected cometary particles from Comet Wild 2; the other collected interstellar dust.

    （2）High-Speed Fly-Through

       · In 2004, Stardust flew through the comet’s coma at roughly 6 km/s.

       · Dust particles penetrated into the aerogel, carving elongated tracks as they decelerated.

       · A density-graded aerogel (low → high density) reduced impact shock even further.

    （3）Return to Earth

       · After collection, the aerogel panel folded into a return capsule.

       · The capsule reentered Earth’s atmosphere in 2006 and landed in Utah.

       · Scientists cut out individual tracks and particles for laboratory study.

3. Future Potential of Aerogels in Space Applications (In-Depth)

    Aerogels already fly on NASA missions—e.g., Mars Pathfinder, Spirit, and Opportunity rovers used them for thermal insulation.
Future applications are even broader.

A. Extreme Thermal Management for Spacecraft

    （a）Ultra-Light Insulation for Satellites & Deep-Space Missions

       · Aerogels provide extremely low thermal conductivity.

       · They can reduce mass compared to foam or multi-layer insulation (MLI).

    （b）Thermal Protection for Mars/Lunar Rovers

       · Mars rovers used aerogel blankets to survive freezing nights.

· Future lunar south-pole rovers and Europa/Enceladus landers may rely on aerogel insulation to reduce heater power consumption.

    （c） Cryogenic Fuel Tank Insulation

       · Aerogel can reduce boil-off losses for liquid hydrogen, oxygen, or methane tanks.

       · Relevant for upper stages, lunar bases, and in-space propellant depots.

B. Planetary Surface “Localized Terraforming” (Solid-State Greenhouses)

    Recent research shows:

       · A 2–3 cm silica aerogel layer can trap enough sunlight on Mars to warm the surface beneath above 0°C,

       · while blocking harmful UV radiation.

    This supports:

       （a） Passive-heated greenhouses or farms on Mars

       （b）Small warm “habitat islands” without terraforming the whole planet

       （c）Composite building panels combining regolith + aerogel

These are realistic short-to-mid-term technologies for Mars surface missions.

C. Communication and Radar Applications (Excellent for PI Aerogels)

    Your area—polyimide (PI) aerogels—has major potential in aerospace RF systems.Why?

       · Extremely low dielectric constant

       · Very low loss at high frequencies

       · Ultra-lightweight

       · Can be flexible for deployable structures

    Potential uses:

       （a） Lightweight satellite antenna substrates

       （b）Large deployable phased-array antennas

       （c）Flexible radomes wrapped around spacecraft bodies (“conformal antennas”)

       （d）Low-noise RF/communication electronics insulation

This is a highly promising segment for future satellite constellations, deep-space probes, and high-bandwidth communications.

D. Radiation & Micrometeoroid Protection (Future Concepts)

    Possible development directions:

       · Doping aerogel with hydrogen-rich polymers, boron, or lithium for radiation shielding

       · Using aerogel layers in Whipple shields to absorb impact energy

       · Creating ultra-light shield structures for long-duration crewed missions

These remain research-stage but strategically important.

E. Advanced Scientific Sampling and Analysis

    Following Stardust, aerogels may be used to capture particles from:

       （a）Enceladus and Europa plume flythroughs

       （b） Comet and asteroid flyby missions

       （c） Orbital space dust monitoring systems

    Aerogels enable intact capture and later high-precision laboratory analysis.

F. Environmental Control & Life-Support Systems

    Because of their large surface area and tunable chemistry, aerogels could support:

       · CO₂ capture

       · Trace contaminant removal

       · Water purification systems

       · Catalyst supports for chemical processing

    Useful in spacecraft cabins or off-world habitats.

Summary

    NASA uses aerogel to capture cosmic dust because it provides a unique combination of:

       · Soft capture at hypervelocity

       · Transparency for tracking

       · Clean, inert chemistry

       · Nanoporous trapping ability

    Looking forward, aerogels—especially silica and polyimide types—may play transformative roles in:

       · Spacecraft thermal management

       · Mars and lunar surface habitats

       · Satellite antennas and radar systems

       · Radiation and impact shielding

       · Cryogenic fuel storage

       · Scientific sampling

       · Life-support and environmental systems

1. Main Types of Aerogels Known Today

    (1) Silica Aerogel (SiO₂ Aerogel) — the Most Mature and Widely Used

       · The world's most common and commercially mature aerogel

       · Based on a Si–O–Si nano-porous structure

       · Applications: building insulation, EV battery thermal protection, industrial insulation, architectural glazing, aerospace

    (2) Carbon Aerogel

       Includes RF-carbon aerogels, graphene aerogels, CNT aerogels, etc.

       Key traits:

       · Excellent electrical conductivity

       · Ultra-low density

       · Used in supercapacitors, energy storage, adsorption materials

    (3) Polymer Aerogel

       Includes:

       · Polyurethane (PU) aerogel

       · Polyimide (PI) aerogel

       · Epoxy aerogel

       Traits:

       · Flexible

       · Better mechanical integrity

       · Thermal resistance typically 200–400°C

       · Used in aerospace, lightweight insulation, flexible components

    (4) Metal Oxide Aerogel

       Examples:

       · Alumina (Al₂O₃) aerogel

       · Zirconia (ZrO₂) aerogel

       · Titania (TiO₂) aerogel

       Traits:

       · High-temperature resistance (up to 1000–1200°C)

       · Often used in catalysts, aerospace heat shields, extreme-temperature insulation

    (5) Biomass / Bio-Based Aerogel

       Examples:

       · Cellulose aerogel

       · Alginate aerogel

       · Chitosan aerogel

       Traits:

       · Biodegradable, environmentally friendly

       · Used in medical, filtration, adsorption

       · Still mainly semi-industrial or research-stage

 2. Differences: Silica Aerogel vs Other Aerogel Types

    Below is the version most useful for customer education and sales discussions:

    (1) Material Structure & Stability

       Notably, silica aerogel stands out for its unparalleled long-term structural stability paired with complete chemical inertness—attributes that make it indispensable in harsh environments where material degradation risks are unacceptable.

    (2) Performance Differences

       For most industrial and consumer scenarios, silica aerogel delivers the optimal balance of insulation performance, non-combustibility, and cost-effectiveness—addressing the core requirements of safety and efficiency simultaneously.

    (3) Commercial Readiness

    Silica aerogel is the only type already used at global industrial scale.

    (4) Application Suitability

 3. Summary: Why Silica Aerogel Is Unique

    (1) Best insulation performance

       World's lowest thermal conductivity among solids.

    (2) Fully non-combustible (A1)

       Essential for EV safety, building fire safety, and industrial. applications.

    (3) Most commercially scalable

       Silica aerogel has a mature, global supply chain.

1. Chemical Composition
    Silica aerogel is primarily composed of silicon dioxide (SiO₂) — the same material found in glass and quartz sand.

    It is chemically stable, non-toxic, odorless, and non-corrosive. Its internal structure is a silica–oxygen network that does not react with moisture or release harmful substances.

 2. Health and Safety Considerations

    Although silica aerogel is non-toxic, it is important to recognize that certain forms or handling conditions may pose minor physical risks:

    (1) Dust Inhalation

       · During cutting, crushing, or processing, fine silica dust may be released.

       · These particles are extremely light and small, and long-term inhalation could irritate the respiratory tract — similar to silica dust exposure in industrial environments.

       · Protective masks (N95 or higher) and goggles are recommended when handling loose or powdered aerogel.

    (2) Skin Irritation

       · Dry silica aerogel has a highly adsorptive surface that can draw moisture from the skin.

       · Prolonged contact may cause dryness, mild itching, or irritation.

       · Use protective gloves and apply moisturizer after handling.

    (3) Environmental and Toxicological Safety

       · Silica aerogel is environmentally friendly, non-radioactive, and does not emit toxic gases.

       · It contains no formaldehyde, benzene, or asbestos, and is widely certified under REACH, RoHS, and MSDS standards for safety and sustainability.

 3. Summary Table

     Conclusion：Silica aerogel itself is non-toxic and environmentally safe, but proper protective measures should be taken when handling its powder or dust form. It is widely recognized as a green, sustainable, and high-performance insulation material.

1. Origin of the Knudsen Effect

    The Knudsen Effect is named after Martin Hans Christian Knudsen (1871–1949), a Danish physicist who made pioneering contributions to the study of rare gas dynamics and molecular transport phenomena.In the early 20th century, Knudsen investigated how gas behavior changes when confined in narrow capillaries or pores, where the size of the channels is comparable to the mean free path of gas molecules.Through his experiments between 1909 and 1911, Knudsen discovered that:

       · When the pores or tubes are extremely small, gas molecules collide more frequently with the walls than with each other.

       · This changes gas flow and heat transfer behavior dramatically, deviating from classical continuum (Navier–Stokes) theory.

    These discoveries led to two famous phenomena bearing his name:

    Knudsen's findings laid the foundation for modern microfluidics, vacuum technology, and nanoporous material science — including aerogels.

2. What Is the Knudsen Effect?

    The Knudsen Effect refers to the phenomenon that occurs when the pore size of a material becomes comparable to or smaller than the mean free path of gas molecules.In such a situation, gas molecules collide more frequently with the pore walls than with each other, which significantly reduces the thermal conductivity of the gas phase inside the pores.

       · The mean free path (λ) is the average distance a gas molecule travels between two collisions.

       o For air at room temperature and atmospheric pressure, λ ≈ 70 nm.

3.  Knudsen Number (Kn)

    The strength of the Knudsen effect is represented by the Knudsen number, defined as: Kn=λ/r ,where:

       · λ = mean free path of gas molecules

       · r = pore radius

    Depending on the value of Kn, heat transfer behavior changes:

4. How It Works in Aerogels

    In silica aerogels, the pore sizes are typically 10–100 nm, which are comparable to or smaller than the mean free path of air molecules.
This means ( Kn>1 ), so the system is in the free molecular regime, where the Knudsen effect is very strong. As a result:

       · Gas molecules are trapped in nanopores and mostly collide with the solid silica walls, not with each other.

       · These wall collisions are mostly random reflections, transferring very little energy.

       · Therefore, the gas-phase thermal conductivity is greatly suppressed — often 1/10 or less of that of free air.

5. Components of Aerogel Thermal Conductivity

    The total thermal conductivity of aerogel (k_total) has three parts: k_total=k_solid+k_gas+k_radiation 

       · k_solid: heat conduction through the silica skeleton (very low due to its sparse structure)

       · k_gas: heat conduction through the air in pores (strongly reduced by the Knudsen effect)

       · k_radiation: heat transfer by thermal radiation (significant only at high temperature)

    The Knudsen effect mainly reduces (k_gas), which is why aerogels have extremely low total thermal conductivity (typically 0.012–0.018 W/m·K).

6. Summary

1. Structural Nature — Extremely Porous 3D Network with Ultra-high porosity (>90%)

    Silica aerogel typically has a porosity between 90% and 99.8%, meaning:

       · Only 1–10% of its volume is solid material;

       · The rest is air-filled voids.

    As a result:

       · The load-bearing cross-sectional area is extremely small;

       · Stress concentrates on the thin silica necks connecting nanoparticles;

       · Once one link breaks, a cascade collapse occurs through the network.

Analogy: It’s like a 3D scaffold made of glass needles — extremely light, but very easy to break.

 2. Chemical Bond Nature — Strong but Brittle Si–O–Si Bonds

    The silica skeleton is built from Si–O–Si covalent bonds, which are:

       · Strong (bond energy ≈ 450 kJ/mol), but

       · Directional and non-ductile — they cannot deform plastically like metallic bonds.

    Therefore, when external stress exceeds the critical point, the bonds fracture suddenly instead of yielding.

    In other words: Once a Si–O–Si chain is overstressed, it snaps instantly rather than absorbing energy by deformation.

3. Microstructural Fragility — Stress Concentration at Nanoscales

       · Primary particle size: 10–50 nm

       · Particles are linked by thin “neck-like” bridges

       · Each node has a low coordination number, so load transfer paths are few

    When force is applied:

       · Local bonds break first,

       · The network collapses locally,

       · Microcracks propagate into macroscopic fractures.

4. Drying Process Effects — Capillary Forces Create Microcracks

    During the sol–gel process, the drying stage can introduce residual damage:

       · In non-supercritical drying, capillary pressure can crush the delicate gel network;

       · Even in supercritical drying, minor shrinkage or microcracks may remain;

       · These become stress initiation sites under later mechanical loading.

 5. Macroscopic Mechanical Properties — Very Low Modulus and Fracture Toughness

    These values show: Silica aerogel’s fracture toughness is about 1/10 of glass and 1/1000 of metals,making it almost incapable of resisting bending, compression, or impact.

6. Methods to Improve Toughness

    Researchers and manufacturers are developing several strengthening strategies:

    (1)Fiber Reinforcement

       · Introduce glass, aramid, or polymer fibers;

       · Create aerogel blankets or composite panels;

       · Greatly improves flexural and compressive strength.

    (2)Organic–Inorganic Hybridization

       · Graft flexible polymer chains (e.g., PDMS, PVA, PMMA) onto silica skeletons;

       · Increases elasticity and crack resistance.

    (3) Nanostructure Optimization

       · Control particle size, neck thickness, and pore size distribution;

       · Build hierarchical porous networks to enhance energy absorption.

1. Core Physics: Capillary Pressure (Laplace Pressure)
     · During drying, liquid–gas interfaces form menisci inside nanopores, exerting negative capillary pressure on the fragile skeleton:

P=2γcos⁡θrP = \frac{2 \gamma \cos \theta}{r}
    · γ\gamma: surface tension of solvent
    · θ\theta: contact angle (for hydrophilic surfaces, θ≈0∘\theta \approx 0^\circ, cos⁡θ≈1\cos \theta \approx 1)
    · rr: pore radius (smaller pore → higher stress)
    · Magnitude example (hydrophilic case):
       o Ethanol: γ≈0.022 N/m,r=10 nm⇒P≈4.4 MPa\gamma \approx 0.022\ \text{N/m}, r=10\ \text{nm} \Rightarrow P \approx 4.4\ \text{MPa}
       o Water: γ≈0.072 N/m,r=10 nm⇒P≈14.4 MPa\gamma \approx 0.072\ \text{N/m}, r=10\ \text{nm} \Rightarrow P \approx 14.4\ \text{MPa}

    Such stress is far above the yield strength of the “wet” silica skeleton, leading to elastic–plastic deformation, pore collapse, shrinkage, densification, or even cracking.

2. Structural & Chemical Factors
    · Smaller pores / narrow distribution → stronger capillary stress.
    · Insufficient neck growth (weak skeleton) due to poor aging → prone to irreversible plastic shrinkage.
    · Surface state: hydrophilic Si–OH surfaces (low θ\theta) → high stress; hydrophobic surfaces (high θ\theta) reduce stress.
    · Solvent: high γ\gamma (e.g., water) increases stress.
    · Sample geometry: thick monoliths develop drying gradients → cracks; thin films/felts are less prone.
    · Pre-shrinkage (syneresis) during gelation/aging can set the stage for further collapse.

Summary: Shrinkage mainly comes from capillary pressure; small pores, hydrophilic surfaces, high-γ\gamma solvents, weak skeletons, and thick parts all worsen it.