Considerations for Selecting an Adhesive for Space Applications

MatWeb Featured Article
By Master Bond, Inc.

Epoxies for Space Applications

Adhesives play a vital role in space applications, where environmental conditions are significantly harsher than on Earth. The high vacuum environment in space, combined with extreme temperatures create demanding challenges for material selection. Also, cryogenically low temperatures, intense solar heat, Low Earth Orbit (LEO) as well as geostationary orbit (GEO) conditions, and high radiation intensities in deep space further complicate adhesive design. This article explores how specialized low-outgassing epoxies enable reliable and durable performance in various space environments.

Adhesives: A Critical Consideration in Spacecraft Design

Adhesives and polymeric materials play a vital role in spacecraft construction, supporting structural, mechanical, and electronic functions such as bonding, potting, encapsulation, coating, sealing, and staking. In many applications, adhesives are shielded from direct exposure to harsh elements like atomic oxygen and ionizing radiation, as they are typically enclosed within the spacecraft or positioned between surface components. However, regardless of their placement, adhesives used in space must withstand high vacuum conditions and extreme cold temperatures, maintaining performance without compromising the integrity of other spacecraft components.

Challenges and Risks in Adhesive Use

• Outgassing:
• Many polymeric materials release volatile compounds in the vacuum of space. Difficultly meeting application requirements— such as high bond strength, thermal performance and chemical resistance
• These volatiles can condense on critical components, leading to:
• Fogging or clouding of optical and electro-optical systems.
• Disruption of circuit continuity.
• Altered optical properties, such as reflectance and absorbance.
• Proximity to sensitive devices:
• Adhesives used near electronic and optical components require stringent outgassing controls to prevent contamination and ensure system reliability.
• Mitigation Strategies:
• Control over outgassing levels is critical to prevent contamination and resultant degradation of mission-critical systems.
• Selecting materials specifically designed for the space environment safeguards durability and performance under extreme conditions.

By addressing these challenges, adhesives contribute significantly to the success and longevity of spacecraft in demanding operational environments.

Low Outgassing Epoxies: A Versatile Solution

Epoxies are highly adaptable polymer compounds known for their excellent strength, chemical resistance, and ability to adhere to a wide range of materials. They can operate under extreme temperature conditions, from cryogenic lows of 4K to over 400°F, making them suitable for demanding applications. Specialty epoxies offer excellent toughness and flexibility while still passing stringent low outgassing requirements.

NASA Low Outgassing Specification

Master Bond offers numerous one- and two-part epoxies specially designed to meet or exceed NASA's low outgassing specification, ASTM E595. These formulations are tailored to meet specific performance requirements, offering a range of mechanical, thermal, optical, electrical, and physical properties.

Customizable Performance Properties

Epoxies can be engineered with various attributes to suit unique applications. For example, adding inorganic fillers allows formulators to modify properties such as:

• Viscosity
• Strength
• Thermal expansion
• Electrical conductivity
• Thermal conductivity

One-Part vs. Two-Part Epoxies

• One-part epoxies: Require no mixing but typically need heat curing to achieve optimal performance.
• Two-part epoxies: Most can cure at ambient temperatures after mixing but benefit from post-curing with heat.

Heat curing plays a critical role in reducing outgassing by increasing the crosslink density of the polymer. For low outgassing applications, formulators often recommend a heat cycle after initial curing. By offering such a wide range of properties and customization options, low outgassing epoxies provide reliable and versatile solutions for space and other high-performance applications.