Cryogenic Insulation with Gas-Circulating Cavities
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Solution Overview
Problem
Existing cryogenic tank insulation technologies are not optimized for mechanical and thermal performance across all phases of use, particularly in partial or secondary vacuum conditions during flight, leading to significant propellant evaporation losses and increased weight.
Innovation Solution
A combination of a rigid closed-cell polyetherimide foam substrate with a multilayer radiative insulation and an upper layer of closed-cell material with cavities for gas circulation, allowing for enhanced thermal performance and mechanical protection without excessive mass addition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional thermal insulation materials (polyvinyl chloride, polyurethane, polyisocyanurate) are used with thickness of 20-25 mm, then mechanical strength is maintained, but thermal performance in vacuum conditions deteriorates leading to significant propellant evaporation losses
Solution Approach 1:
The patent applies composite materials by combining conventional foam insulation with radiative multi-layer insulation (MLI) consisting of alternating reflective layers and spacer layers. This composite structure leverages the mechanical strength of the foam substrate while the MLI layers provide superior thermal reflection in vacuum conditions, significantly reducing thermal losses and propellant evaporation during flight phases.
Solution Approach 2:
The invention changes the thermal insulation parameters by introducing a multi-layer radiative barrier system with specific reflectivity characteristics. The MLI structure changes the thermal radiation parameters by creating multiple reflective interfaces that reduce radiative heat transfer in vacuum, thereby improving thermal performance without compromising mechanical integrity.
2Loss of energy
If radiative multi-layer insulation (MLI) is used to improve thermal performance in vacuum, then thermal insulation efficiency increases, but mechanical fragility and sealing requirements worsen
Solution Approach 1:
The patent employs flexible thin film structures for the MLI layers, using thin metallic or dielectric films that provide effective radiative insulation while maintaining flexibility. These thin films are integrated with a foam substrate that provides the necessary mechanical strength, allowing the MLI to conform to tank surfaces without requiring rigid support structures.
Solution Approach 2:
The foam substrate acts as an intermediary between the MLI layers and the external environment, providing mechanical strength and structural support while the MLI layers focus on thermal insulation. This intermediary role allows each component to optimize its primary function without compromising the other.
3Device complexity
If MLI insulation is used without sealing, then device complexity is reduced, but harmful cryopumping effects increase due to air contamination
Solution Approach 1:
The foam substrate provides self-service by acting as both the structural support and the primary sealing barrier. The closed-cell structure of the foam naturally prevents air infiltration without requiring additional complex sealing systems, while still allowing the MLI layers to function effectively in reducing thermal radiation.
Solution Approach 2:
The foam insulation creates an inert environment by maintaining a sealed internal atmosphere that prevents air from reaching the cryogenic propellant. This inert barrier eliminates the need for active helium ventilation systems while preventing cryopumping effects that would occur with air contamination.
4Loss of energy
If insulation thickness is increased to improve thermal performance, then thermal losses are reduced, but launcher payload capacity deteriorates due to increased mass
Solution Approach 1:
The patent uses composite materials combining foam insulation with thin MLI layers to achieve superior thermal performance without the mass penalty of thick single-layer insulation. The MLI layers provide high thermal resistance per unit mass through radiative reflection, allowing thinner overall insulation packages that reduce launcher payload mass while maintaining effective thermal protection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Significantly reduces thermal flux and propellant evaporation during flight phases, resulting in substantial payload gains while maintaining mechanical integrity and reducing the need for helium ventilation.
Implementation Method 1
an insulating upper layer constructed in the form of a rigid covering provided with cavities open towards the substrate... combination of an insulation substrate deposited on the structure to be insulated... and an insulating upper layer constructed in the form of a rigid covering provided with cavities open towards the substrate
Implementation Method 2
made of closed-cell rigid foam made of polyvinyl chloride, polyurethane filled or not with glass, polyisocyanurate or phenolic resins
Implementation Method 3
closed-cell rigid foam... thermally insulating material... to limit thermal entry
Implementation Method 4
allowing the conditioning of the substrate by the circulation of a gas in the within the cavities, so as to maintain an excess pressure relative to the outside while waiting on the ground, which prevents the entry of air onto the substrate likely to produce cryopumping
Data Source
AI summary
This thermal insulation component comprises a substrate, typically consisting of a closed-cell material layer (1) and a radiative multilayer insulation layer (2); it is complemented by a covering in the form of an upper layer (4) of thermally insulating material with cavities (5) for conditioning a gas (7) that prevents air from accessing the substrate. The insulation (2) produces significant radiation reflection, the lower layer (1) creates a first thermal barrier with the underlying structure (3), and the upper layer (4) protects the insulation (2) while itself providing a significant thermal barrier to the cavities, which are emptied of gas when the pressure decreases, particularly during launch vehicle flight. The conditioning gas can be nitrogen. Application to space launch vehicles.