As human probes journey toward Mars, lunar bases move from concept to planning, and commercial satellite constellations fill low Earth orbit, aerospace engineering demands materials that transcend terrestrial limits. In the harsh environment of deep space—characterized by near-perfect vacuum (<10⁻⁶ Pa), intense ultraviolet (UV) radiation, atomic oxygen (AO) erosion, extreme thermal cycling (–180°C to +12 h 0°C), and bombardment by high-energy particles—most organic polymers rapidly degrade, embrittle, or outgas, contaminating sensitive optical and electronic systems. High-purity silicone rubber, thanks to its unique molecular architecture and tunable chemical inertness, has become an irreplaceable “flexible messenger” in spacecraft sealing, vibration damping, and thermal control systems—silently safeguarding humanity’s frontier of exploration in the cosmic silence.

I. The Harsh Realities of the Space Environment for Polymers

1. Vacuum Outgassing

Materials stable at Earth’s atmospheric pressure release volatile compounds (e.g., plasticizers, unreacted monomers) in vacuum. These condense on lenses, solar arrays, or sensors, causing:

Reduced optical transmittance;

Degradation of thermal control coatings;

Electrical leakage in high-voltage circuits.

2. Atomic Oxygen (AO) Erosion

In low Earth orbit (200–700 km), highly reactive AO oxidizes organic surfaces, leading to erosion, surface pitting, and powdering.

3. UV and Particle Radiation

Solar UV (especially <200 nm) and cosmic rays break C–C and C–H bonds, inducing chain scission or crosslinking.

4. Thermal Cycling Fatigue

Satellites experience a full thermal cycle (–150°C to +120°C) every ～90 minutes in orbit. Repeated expansion and contraction cause microcracks in less resilient materials.

II. Silicone Rubber’s Space-Worthy Advantages

While not flawless, silicone rubber outperforms other elastomers in critical areas:

1. Exceptionally Low Outgassing

The Si–O backbone (bond energy: 452 kJ/mol) with methyl side groups offers high thermal stability.

High-purity addition-cure silicones, after rigorous vacuum devolatilization, achieve:

Total Mass Loss (TML) < 0.5%

Collected Volatile Condensable Materials (CVCM) < 0.01%

This meets NASA’s stringent ASTM E595 standard (TML ≤ 1.0%, CVCM ≤ 0.1%).

By comparison, standard silicones may have TML of 2–5%, and epoxies can exceed 10%.

2. Superior Radiation Resistance

The Si–O bond resists cleavage by γ-rays and electron beams.

Nanofillers like cerium oxide (CeO₂) or silicon carbide (SiC) scavenge free radicals, enhancing durability.

After 100 kGy irradiation, mechanical properties retain >80% of original values.

3. Wide-Temperature Elasticity

Glass transition temperature (Tg) ≈ –120°C enables flexibility even at lunar night temperatures (–180°C).

Phenyl-modified silicones (with phenyl side groups) further depress Tg to –140°C, ideal for deep-space missions.

4. Moderate Atomic Oxygen Resistance

AO exposure forms a protective silica (SiO₂) passivation layer on the surface, slowing further degradation.

While inferior to polyimides (PI) or fluoropolymers, performance is significantly enhanced by nano-coatings of SiO₂ or Al₂O₃.

III. Key Aerospace Applications

表格

Application   Function Requirements

Optical System Sealing      O-rings in Hubble & James Webb Space Telescope interfaces Zero contamination, no particle shedding, minimal scatter in IR/visible bands

Solar Array Hinge Damping     Shock absorption during deployment    Stable under combined UV/electron irradiation, long-term elasticity

Spacesuit Joint Seals  Wrist and helmet rotary joints in ISS EMU suits    Airtight yet flexible, functional at –100°C during EVAs

Propulsion System Seals    Valves in cold-gas or ion thrusters (using N₂, Xe) Low compression set, reliable after thousands of cycles

IV. Material Qualification & Certification

All space-grade silicones must undergo:

Listing in the NASA Outgassing Database;

Compliance with ESA ECSS-Q-ST-70-02C standards;

Ground-based simulation tests:

100+ cycles of Thermal Vacuum (TVAC);

Combined UV/AO/electron irradiation;

Post-exposure assessment of mechanical and electrical properties.

Leading suppliers—including Dow Corning, Wacker, and Nusil—offer certified “Space Qualified” silicone rubber series.

V. Challenges and Future Directions

Long-Term Aging Data Gap: Most ground tests simulate 5–10 years; deep-space missions may last 20+ years.

Micrometeoroid Vulnerability: Soft materials are prone to puncture; hybrid designs with impact-resistant layers are being explored.

In-Situ Manufacturing: Future lunar or Martian bases may require on-demand 3D printing of seals, driving R&D into printable, space-certifiable silicones.

Conclusion

On the silent stage of the cosmos, silicone rubber is a quiet guardian. It emits no light, yet ensures telescopes capture galaxies billions of light-years away; it provides no thrust, yet guarantees precise ignition of propulsion systems; it does not breathe, yet maintains the life-sustaining atmosphere within a spacesuit. This supple silicon-based material responds to the ultimate trials of vacuum and radiation with molecular-level stability. As humanity ventures deeper into the stars, such soft yet resilient barriers will continue to uphold the final arc of our exploratory reach—because true voyages into the unknown begin with the most meticulous reverence for detail.



Ceramic refractory flame retardant silicone rubber