When it comes to manufacturing satellites, aircraft, and spacecraft, adhesives are the superior choice compared to any other binding method available. With their capacity to handle extreme heat and radiation, epoxies are considered the ideal choice of adhesive for the space industry.

You have to remember that epoxies come in a variety of formulations and you have to be careful about selecting the right epoxy adhesives for the required space application. Let’s consider a scenario where the aircraft ascends to higher altitudes, and the atmosphere gradually becomes thinner, leading to depressurization and a hostile environment. The use of adhesives that cannot withstand such a condition can cause inevitable harm, therefore stressing the need to carefully select epoxy adhesives that can maintain their structure and properties even in extreme temperatures, radiation and microgravity.

In this blog, we will guide you through the challenges of the space environment for equipment manufacturers and the key factors that you should consider while selecting adhesives for aerospace applications.

A] Understanding The Challenges Of Space Environments

The environment in space is very different from the conditions on Earth. Epoxies that work well on the ground might not be able to withstand the conditions in space. There are a number of challenges that can hinder the serviceability of the adhesives for spacecrafts. Here are a few challenges that these adhesives have to overcome.

• Vacuum: Certain adhesives use atmospheric pressure to cure and bond. However, in the vacuum of space, the adhesives used must be able to cure, bond and maintain the bond without atmospheric pressure.
• Extreme temperatures: Space travel can be subjected to melting hot and freezing cold temperatures. Hence, it is necessary to select high-performance adhesives for space that can withstand such extreme temperatures.
• Radiation: Without the protection of our atmosphere, solar radiation can corrode metals and degrade the chemical structure of adhesives. Long exposure to radiation can break down the adhesives and, by extension, the equipment.
• Outgassing: In a low-pressure environment, many adhesives release chemicals and gases, this is called outgassing. Outgassing can degrade the chemical and mechanical properties of the adhesives and also affect the electrical and optical components of the equipment.
• Microgravity: Without the Earth’s normal gravity, most adhesives do not cure as intended, which can lead to incomplete bonding. It is very risky as the components can separate midway affecting the intended result.

B] Key Factors For Adhesive Selection In The Space Industry

1. Temperature Resistance

Satellites, aircraft, spacecraft and other carriers that must travel to space face extreme hot and cold temperatures. These extreme temperature fluctuations can damage the structural and chemical properties of standard adhesives, rendering them useless. This can compromise the vessel’s safety and integrity and lead to the project’s failure. The adhesive must be capable of withstanding such extreme temperatures and the fluctuations it will experience throughout the equipment’s lifetime.

Specialised space grade epoxy systems are typically used to bond the components of spacecraft. These adhesives do not lose their chemical or mechanical properties and maintain their flexibility, viscosity, and strength even in the face of extreme temperature fluctuations.

2. Vacuum Compatibility

One of the primary concerns of aircraft manufacturers when choosing adhesives for space projects is the adhesive’s serviceability in a low vacuum environment. As the system has to work in a very high vacuum in space, approx 10-8 torr, outgassing is a very real possibility. Any outgassing from the adhesive could lead to the failure of crucial electrical and optical components of the system.

Low outgassing epoxy adhesives are recommended for any spacecraft which are to be operated in low-vacuum conditions. These specially designed epoxies do not release any gases or chemicals, even in a low vacuum environment. Make sure to test the epoxy compounds under rigorous conditions before application. NASA’s ASTM E-595 low outgassing test is the standard against which you must measure the reliability of the adhesive.

3. Radiation Resistance

Radiation resistance is a crucial factor in a space-grade adhesive as, without the cover of the atmosphere, there is no protection from solar and cosmic radiation. Space is filled with harmful radiation, which can degrade the delicate components of the equipment. Typical adhesives are not designed to face these conditions and would lose their integrity, viscosity and chemical properties like thermal and electrical conductivity when exposed to radiation.

To ensure optimal results for use in space applications, look for bespoke adhesives which resist the effects of solar and cosmic radiation. Radiation resistant epoxies are subjected to strict testing by exposing them to radiation for extended periods of time and then analysing their results. Mechanical strength, chemical properties like thermal and electrical conductivity stability, and texture are some of the crucial parameters you should consider.

4. Mechanical Properties

The environmental conditions are drastically different in outer space than as compared to on Earth; as a result, adhesive materials tend to act differently. It is crucial to consider the adhesive’s mechanical properties and choose one that suits your needs. The epoxy must be able to provide strong adhesion to the components in dynamic environments like zero gravity, high vacuum, and extreme temperatures. It is important to consider your specific requirements like shock and vibration resistance, tensile strength, and high peel and shear strength.

Test the adhesive for all the mechanical properties that you require before applying it to the components.

C] Outgassing Test And Certification

One of the most common problems manufacturers face is the risk of outgassing adhesives. Manufacturers have to deal with the high vacuum and low-pressure environment and select aerospace grade epoxy that does not leak. Any outgassing from the adhesive could lead to failure of crucial components of the system.

NASA developed the ASTM E-595 low-outgassing test standard to avoid such failure during operation. This test involves collecting volatiles from the test specimen and weighing the condensate to determine the following:

• CVCM: The amount of collected volatile condensable materials (CVCM) on the collector plate.
• TML: The amount of total mass loss (TML) by the sample
• WVR:The amount of water vapour regained (WVR) by the sample

The material is said to pass or fail the test based on the following conditions:

• CVCM < 0.1% and TML < 1% – Pass
• CVCM < 0.1% and TML > 1% – Pass if TML – WVR <1%
• CVCM > 0.1% or TML – WVR > 1% – Fail

Kohesi Bond has specially formulated epoxy adhesives, sealants, coatings, potting and encapsulation compounds capable of providing excellent performance at high temperatures and down to 4K (-269.15°C). They are capable of passing NASA outgassing standards. Furthermore, these epoxy systems can provide optical clarity, thermal and electrical conductivity/insulation, chemical resistance, superior mechanical strength and toughness.

Conclusion

Adhesives remain one of the best means of connecting components for aerospace applications. However, all adhesives might not be suitable for aerospace applications as the environment is vastly different and dynamic. Selecting the right adhesives that can withstand the equipment’s challenges at elevated heights and in space is important.

It is essential to test the sealing, coating and encapsulation compounds used for aerospace applications and use only those which are capable of passing rigorous tests. If you are looking for tried and tested adhesive epoxies for various space components, satellites, aeroplanes, unmanned air vehicles (UAVs) and sensors or need a bespoke adhesive compound, contact us today! Kohesi Bond’s expert adhesive experts are happy to help you find the best-suited product for aerospace applications.

Utsav Shah

Utsav Shah is a 34-year-old entrepreneur with a passion for scientific discovery. Utsav’s journey began with a deep dive into materials science, earning degrees from USC and the Institute of Chemical Technology. He’s the visionary founder of Kohesi Bond, a top-rated adhesive manufacturer, and Cenerge Engineering Solutions, a leader in heat exchangers and cryogenic pumps. With over a decade of experience, Utsav consults across various industries, ensuring they have the perfect adhesive solution for their needs. Connect with him on LinkedIn!