Aerospace Grade Epoxies: Meeting NASA’s Low Outgassing Standards with Kohesi Bond

In space, every molecule matters. One microscopic layer of condensed volatiles on a star tracker lens or a thermal radiator can distort measurements that entire mission timelines depend on. 

This phenomenon, outgassing, is predictable, measurable, and, if ignored, mission-threatening. 

When polymers encounter vacuum or sharp thermal gradients, their trapped monomers, oligomers, plasticisers, and absorbed moisture transition into vapour and migrate through the spacecraft. And in a vacuum as unforgiving as 10⁻⁶ to 10⁻⁸ torr, even a few micrograms of residue can mean optical attenuation, electronic drift, or thermal imbalance.

NASA originally developed the test method, which is now standardised as ASTM E595 under ASTM International for evaluating outgassing of spacecraft materials. 

Whether we’re talking about large GEO satellites, deep-space telescopes, CubeSats, or optical benches, materials must demonstrate extremely low volatile release to be considered safe for flight.

This danger is exactly where highly engineered aerospace-grade epoxy systems come into play. 

They offer the structural strength and thermal stability engineers demand without adding molecular contamination. 

At Kohesi Bond, we engineer aerospace-grade epoxy systems precisely tested to meet NASA’s stringent low-outgassing standards, ensuring spacecraft operate cleanly, predictably, and reliably over multi-year missions.

A] What is Outgassing, and Why Does It Matter in Aerospace Applications?

1. Definition and Mechanism

Let’s begin with a clear, technical definition.

Outgassing is the diffusion, desorption, and evaporation of volatile species from a polymer matrix when exposed to vacuum or thermal energy.

Under vacuum, the vapour pressure differential accelerates the release of:

• Unreacted monomers
• Solvents or catalysts
• Moisture
• Decomposition products

Outgassing behaviour approximately follows an Arrhenius-type temperature dependence:

D = D₀ exp(–Eₐ/RT)

Understanding the Equation:

• D: The diffusion coefficient (how fast molecules move out of the material).
• D₀: A pre-exponential factor constant.
• E: The Activation Energy required for a molecule to break free.
• R: The Universal Gas Constant.
• T: Absolute Temperature (in Kelvin).

Why it matters: This equation shows that as temperature ($T$) increases, the rate of outgassing grows exponentially. 

Even a small rise in spacecraft temperature can significantly lower the polymer’s resistance to diffusion, causing a surge in mass loss and potential contamination of nearby sensors.

2. Impact on Aerospace Components

Now picture what happens next.

Volatiles migrate until they reach colder regions such as optical sensors, star trackers, IR detectors, and thermal radiators. There, they condense as nanometre-thin molecular films, leading to:

• Optical contamination: Reduced transmissivity in UV/visible/IR bands
• Electronic interference: Changes in surface resistivity or dielectric behaviour
• Thermal imbalance: Altered emissivity/absorptivity of radiators
• Sensor drift: Contamination on photodiodes and spectroscopic instruments

A contamination layer only 50–100 nm thick can significantly alter radiation absorption curves. This is non-negotiable territory for aerospace engineers.

3. Industry Need for Low-Outgassing Materials

Aerospace, high-vacuum semiconductor fabs, defence payloads, and cryogenic systems all share a fundamental requirement: molecular cleanliness.
Low-outgassing polymers ensure:

• Dimensional stability under load
• Predictable behaviour under radiation and thermal cycling
• Long-term reliability of instrumentation

This is why the search for space-qualified epoxy adhesive systems is so central to mission assurance.

4. Kohesi Bond’s Perspective

From Kohesi Bond’s standpoint, controlling outgassing is an engineering philosophy, not a checkbox. We rely on:

• Purified epoxy resins
• Ultra-stable curing agents
• Vacuum-compatible fillers
• Controlled manufacturing environments

Together, they yield high-performance aerospace epoxy systems engineered for zero-compromise reliability in vacuum conditions.

B] Understanding NASA’s Low-Outgassing Requirements (ASTM E595)

1. Overview of ASTM E595

NASA developed ASTM E595 because early spacecraft missions discovered that uncontrolled polymer outgassing could degrade optics and electronics, even when the adhesive seemed perfectly stable on Earth. This standard quantifies how much volatile material a polymer releases under conditions that mimic space:

• Temperature: 125°C
• Vacuum: < 5 × 10⁻⁵ torr
• Duration: 24 hours
  

2. Key Parameters

ASTM E595 defines two measurable outcomes:

• TML — Total Mass Loss

• • Required: ≤ 1.00%
  • Indicates total volatilisation from the polymer.
    
    

• CVCM — Collected Volatile Condensable Material

• • Required: ≤ 0.10%
  • Represents volatiles that condense on a collector plate, mimicking spacecraft optics.

• WVR — Water Vapour Regain

• • No fixed acceptance limit (used for secondary qualification)
  • Quantifies the amount of moisture the material reabsorbs after vacuum exposure. WVR helps differentiate between true organic volatile loss and simple moisture evaporation, enabling accurate evaluation of borderline results.

Together, these metrics define the molecular cleanliness of an adhesive or polymer under simulated space conditions.

CVCM, in particular, is the parameter optical engineers obsess over, and for good reason.

3. Testing Methodology

Here is the essential sequence:

• Prepare and precondition the sample.
• Record its initial mass.
• Expose to 125°C under high vacuum for 24 hours.
• Collect condensed volatiles on a mirror-finish plate at 25°C.
• Reweigh the sample and the collector to derive:
  • TML = ((m₀ – m₁)/m₀) × 100%

Understanding the Variables:

m₀: The initial mass of the epoxy sample before testing.

m₁: The final mass of the sample after being subjected to 125°C in a vacuum for 24 hours.

Why it matters: If the TML is higher than 1.00%, it indicates the material is unstable. However, if much of that loss is just water (measured by WVR), the material might still be flight-worthy.

This multi-step approach isolates moisture loss from true organic volatilisation, giving engineers a detailed picture of a material’s contamination risk.

While TML tells us what was left of the material, CVCM tells us what actually “stuck” to the cold surfaces of the spacecraft. It is calculated as:

CVCM = ((m_cp1 − m_cp0) / m_0) × 100%

Where:

m_cp0 = Initial mass of the collector plate (“mirror”)

m_cp1 = Final mass of the collector plate after the test

m_0   = Original mass of the epoxy sample

Why it matters: This is the most critical number for optical engineers. A CVCM of more than 0.10% means too many “sticky” molecules are landing on lenses or mirrors, which could fog a telescope or star tracker, potentially ending a mission.

Once testing is complete, the material is evaluated using NASA’s acceptance criteria:

• CVCM < 0.10% and TML < 1.00% — PASS
  The material meets NASA’s low-outgassing requirements without qualification.
• CVCM < 0.10% and TML > 1.00% — CONDITIONAL PASS if (TML – WVR) < 1.00%
  If mass loss is primarily due to moisture and not organic volatiles, the material can still be accepted.
• CVCM > 0.10% or (TML – WVR) > 1.00% — FAIL
  The material poses a contamination risk and is unsuitable for flight hardware.

This pass–fail matrix ensures that only materials with demonstrably low contaminant potential are allowed near sensitive spaceflight assemblies.

4. Compliance Significance

Whether you’re bonding optical benches, potting electronics, or assembling internal spacecraft structures, materials that fail E595 don’t fly. It’s that simple.

5. Kohesi Bond’s Conformance

Every NASA low-outgassing epoxy developed by Kohesi Bond undergoes:

• In-house chemistry screening
• Third-party ASTM E595 verification
• Batch-to-batch consistency checks

This ensures unmatched reliability for space and vacuum platforms.