Sealing at cryogenic temperatures is one of the most demanding engineering challenges in space applications. From embrittlement to installation temperature, multiple issues must be considered–especially when dealing with cryogenic seals for space applications. However, several sealing solutions are also available.
And in the unforgiving environment of space, failure is not an option—and that includes the seals used in cryogenic systems. Whether it is managing the volatile flow of rocket propellants or maintaining the integrity of cryo-cooling systems aboard spacecraft, sealing solutions must perform flawlessly at temperatures approaching absolute zero. These extreme conditions present unique engineering challenges, including material embrittlement, thermal contraction, chemical compatibility, and outgassing.
In this blog post, we discuss
In this article, readers will learn how cryogenic sealing challenges in space applications are addressed through advanced materials, engineered designs, and specialized seal technologies from Advanced EMC.
Cryogenic Seals in Space
Cryogenic technology plays a crucial role in a wide range of aerospace applications, where ultra-low temperatures are not only common but essential. These environments demand precision, reliability, and an uncompromising approach to materials and design, that includes the seals. Here are some of the most common cryogenic systems in space:
Rocket Propulsion Systems: Cryogenic fluids like liquid hydrogen (LH₂) and liquid oxygen (LOX) are frequently used as propellants in launch vehicles. These fluids are stored and pumped at temperatures as low as -253°C, where even minor seal failures can result in fuel loss, combustion instability, or catastrophic failure. Components such as turbopumps, valves, and fuel lines require seals that can withstand both the extreme cold and the rapid pressure changes of launch and ascent.
Spacecraft Cryo-Cooling Systems: In orbit, sensitive instruments—such as infrared sensors, telescopes, or superconducting electronics—must be cooled to cryogenic temperatures to function properly. Cryocoolers and radiative cooling systems often circulate liquid nitrogen or liquid helium to maintain the desired thermal environment. Seals in these systems must maintain tight tolerances to prevent leaks and avoid contaminating vacuum chambers or sensitive electronics.
Storage and Transfer Systems: Both launch pads and spacecraft use cryogenic tanks and fluid transfer lines for fuel and coolant handling. Ground systems must safely load and unload cryogens, while orbital platforms must manage boil-off and resupply operations. These applications place seals under repeated thermal cycling and often involve long periods of static sealing at cryogenic conditions.
The Importance of Seal Integrity at Cryogenic Temperatures
Maintaining seal integrity with cryogenic seals for space applications is a non-negotiable requirement. When seals fail in these environments, the consequences can include:
- Fuel leaks that lead to fire, explosion, or mission failure
- Loss of cooling for critical instruments, degrading performance or causing shutdown
- Contamination of vacuum environments or sensitive optics
- Mechanical damage from fluid escape or pressure imbalance
Unlike ambient-temperature applications, seals in cryogenic systems are expected to perform with zero tolerance for failure, often under high pressure, in vacuum, and across extended mission durations. This means seal materials must not only resist embrittlement and chemical degradation, but also remain dimensionally stable and maintain consistent compression despite significant thermal contraction.
Challenges Related to Cryogenic Seals for Space Applications
Materials behave differently under cryogenic conditions, with issues including embrittlement, thermal contraction and expansion, and material issues.
Embrittlement
One of the most critical challenges in cryogenic sealing is embrittlement: the tendency of materials to become hard, brittle, and prone to fracture at extremely low temperatures. While many materials exhibit flexibility and toughness at room temperature, they can behave more like glass when subjected to cryogenic conditions.
At the molecular level, polymers and elastomers rely on the mobility of their molecular chains to deform and absorb energy. When exposed to ultra-low temperatures, these molecular chains lose mobility and become rigid. This loss of ductility means the material can no longer bend or flex under stress. Instead, it snaps or cracks. This is particularly problematic for dynamic sealing applications, where continuous flexing or movement is required to maintain a proper seal.
For seals in aerospace environments, such as those used in launch systems, fuel lines, or satellite components, embrittlement can lead to catastrophic failure. A seal that fractures under cryogenic conditions may leak or completely lose sealing integrity, allowing volatile fluids like liquid hydrogen or oxygen to escape. The risks range from system performance loss to fire and explosion hazards.
To combat embrittlement, materials must be selected that maintain toughness and elasticity at cryogenic temperatures. Polymers such as PTFE, PCTFE, and UHMW-PE are known for their ability to remain flexible at temperatures as low as -200°C or even lower. These materials resist the transition into a glassy, brittle state, allowing seals to remain functional and resilient despite the severe cold.
However, even within the category of high-performance polymers, embrittlement resistance can vary. For example, PTFE retains flexibility exceptionally well and resists cracking, but it has high CTE and can deform under pressure. In addition, PCTFE offers improved dimensional stability and low permeability, making it less prone to embrittlement and more suited for tight-tolerance applications.
Thermal Contraction and Expansion
In cryogenic sealing applications, thermal contraction and expansion can be a silent but significant threat to system integrity. As temperatures drop to cryogenic levels, every material contracts, but they do not all contract at the same rate. This is due to differences in their coefficient of thermal expansion (CTE), a measure of how much a material expands or contracts with temperature changes.
When polymer seals are housed in metallic hardware—such as stainless steel, aluminum, or titanium—the CTE mismatch becomes a key engineering concern. Polymers generally have much higher CTEs than metals. For instance, PTFE has a CTE that can be up to 10 times greater than that of stainless steel. This means that during cooldown, the polymer seal may shrink far more than the metal housing, potentially leading to …
- Loss of radial or axial interference, allowing gaps to form.
- Reduced sealing force, particularly in static applications.
- Increased leakage risk, especially in vacuum or high-pressure systems.
The reverse can also be true in some dynamic systems: as temperatures fluctuate during launch or orbital operation, differential expansion and contraction can cause seals to shift, extrude, or lose alignment. This is especially problematic in multimaterial assemblies with complex geometries.
Material Issues
There are always potential issues with the type of material chosen for sealing solutions, but this is particularly true in cryogenic applications where seals are exposed to extreme cold and highly reactive fluids. The wrong material choice can result in chemical degradation, embrittlement, or failure due to poor thermal performance, any of which can jeopardize mission-critical systems in space.
Cryogenic fluids, such as liquid hydrogen, oxygen, methane, and helium, are not only extremely cold but also chemically aggressive. For example, liquid oxygen is a powerful oxidizer and can react violently with incompatible materials, while liquid hydrogen’s small molecular size makes it notoriously difficult to seal. Materials that perform well at room temperature may shrink, harden, or crack when subjected to cryogenic conditions, compromising both elasticity and sealing force.
| Cryogenic Fluid | Boiling Point | Primary Use(s) |
|---|---|---|
| Liquid Hydrogen (LH₂) | −252.87°C (−423.17°F) | Rocket fuel (used with LOX in engines like NASA’s RS-25) |
| Liquid Oxygen (LOX) | −182.96°C (−297.33°F) | Oxidizer for rocket propulsion (LOX/LH₂, LOX/RP-1 engines) |
| Liquid Methane (LCH₄) | −161.5°C (−258.7°F) | Propellant in next-gen engines (e.g., SpaceX Raptor, Blue Origin BE-4) |
| Liquid Nitrogen (LN₂) | −195.79°C (−320.42°F) | Thermal management, purging, pressurization, testing life support systems |
| Liquid Helium (LHe) | −268.93°C (−452.07°F) | Cooling superconducting systems, engine purging, tank pressurization |
| Supercritical CO₂ | Near 31°C & 73 atm (not cryogenic) | Coolant and working fluid in closed-loop power systems |
| Hydrogen Slush | Below −252.87°C (partial solid) | Potential advanced fuel |
| Cryogenic Xenon | Below −108.1°C (under pressure) | Ion propulsion (e.g., for satellites, deep-space missions) |
Finally, outgassing and purity must be considered, especially in vacuum or satellite systems. Materials used in these environments must not release volatile compounds that can contaminate sensitive components or optics.
Solutions: Cryogenic Seals for Space Applications
Cryogenic sealing in space is uniquely demanding due to ultra-low temperatures, extreme pressure differentials, vacuum conditions, and the need for long-term reliability with no room for failure. Below are some of the most effective sealing technologies used in aerospace cryogenic environments, each offering distinct advantages depending on the application.
| Seal Type | Best Use Case | Advantages | Limitations |
| Spring-Energized | Dynamic or static sealing | Maintains force at low temps; durable | Cost, complexity |
| Labyrinth Seal | Gas leakage control | Non-contact, long lifespan | Not a positive seal |
| Backup Rings | High-pressure applications | Prevent extrusion of soft seals | Requires correct sizing |
Spring-Energized Seals
Spring-energized seals are the gold standard for cryogenic sealing in space systems. These seals consist of a polymer jacket—typically made from PTFE, UHMW-PE, or PEEK—paired with a metallic energizer spring. The spring maintains a consistent sealing force across a wide range of temperatures and pressures, compensating for material contraction at cryogenic temperatures.
They offer reliable sealing at temperatures as low as -270°C; low friction and wear, even in vacuum environments; and can be customized for static, rotary, or reciprocating applications.
Labyrinth Seals
Labyrinth seals are non-contact seals that rely on a series of tight, interlocking grooves or ridges to restrict gas flow. While not typically used for liquids, they are ideal for sealing gases in low-pressure or high-speed rotating systems where contact-based seals would wear out quickly.
These seals exhibit zero friction and wear, making them ideal for systems with long duty cycles. They are also highly effective at restricting gas leakage in turbine or compressor assemblies, and no lubrication is required, making them suitable for vacuum conditions.
Backup Rings
Backup rings are not seals themselves, but they are critical in cryogenic sealing systems where extrusion resistance is essential. These rigid or semi-rigid rings support soft sealing elements under pressure, preventing deformation and failure, especially when temperature fluctuations cause large swings in material stiffness.
They prevent extrusion of softer polymer seals under cryogenic pressure and improve seal longevity in dynamic or cycling systems. In addition, they are compatible with PTFE, UHMW, and elastomeric seals.
Advanced EMC Cryogenic Seal Solutions for Space
At Advanced EMC Technologies, we specialize in delivering high-performance cryogenic seals for space applications. Our engineering team collaborates closely with our clients to design and develop custom spring-energized and polymer-based seals that perform reliably in extreme low temperatures, vacuum conditions, and chemically aggressive environments. With extensive experience in material selection, including PTFE, UHMW-PE, and PEEK, we ensure optimal compatibility with cryogenic fluids and mission-specific requirements. From fuel handling systems to orbital cryo-cooling units, our solutions are trusted to maintain integrity where failure is not an option.
Conclusion
Cryogenic environments in space present some of the most challenging sealing issues in engineering, encompassing material embrittlement, thermal contraction, and compatibility with volatile cryogenic fluids. Meeting these challenges requires more than just off-the-shelf components—it demands advanced materials, precision engineering, and application-specific design.
At Advanced EMC Technologies, we offer custom sealing solutions that perform reliably in the most demanding aerospace conditions. Whether for launch systems, in-orbit cryogenic storage, or space station cooling systems, our cryogenic seals are engineered to ensure safety, efficiency, and long-term performance.
Contact Advanced EMC today to learn how our cryogenic sealing technologies can support your next space mission.