Folded Core materials for cryogenic CFRP tank insulation

Objective
Tanks to store cryogenic media (e.g. LH2) require very good insulation to prevent the cryogenic medium inside the tank from boiling, as boiled-off media reduces the storage efficiency of the tank. Classical insulation options include foams of various kinds, which on one hand provide successful insulation but on the other hand, come with a lot of issues in application, thickness and combination with surface attached elements of all kinds and in the end significant mass increase. Vacuum insulation of the tank is the most efficient method to prevent heat from entering the cryogenic medium inside the tank. The higher the vacuum the better the insulation performance and the better the storage efficiency for cryogenic media.

The innovative approach is to adapt the vacuum insulation principle to a Carbon Fiber Reinforced Plastic (CFRP) sandwich configuration which can be used for outer tube CFRP tanks.

Main objectives of the CFRP sandwich evacuated structure are:

1. to withstand the mechanical loads that are transferred by the launch vehicle;
2. to provide a sufficient cross section for venting in the core material so that a high vacuum can be applied.

Secondary objectives of the CFRP sandwich evacuated structure are:

1. to minimize heat flux between the face sheets
2. mass-efficient core material
3. cost-efficient core material
4. robust manufacturing process (e.g. core crush, telegraphing, …)

Solution approach
Standard core materials, e.g. Nomex honeycomb come with boundary conditions which increase complexity in manufacturing and do not offer much room for improvement. So, alternatives e.g. foldcore materials shall be screened based on specific launcher data in the fields of thermal conductivity, mechanical loads (compression, shear), minimum required free cross section for evacuation length and width, vacuum level and desired sizes of full-scale application panels. Starting with analytical approach to find a suitable folding and perforation pattern shall be developed. A screening program with the selected material (most promising concept of folding and perforation) wrt mechanical and thermal characteristics shall be conducted. The program should end with a suitable test sample to show the functional performance of the evacuated fold core. An up-scaling perspective to full scale application and serial production (parts/year) shall be provided.

Input
MTA will provide a set of data including all physical constraints of the desired size and performance of the foldcore insulation panel that can be applied to a black upper stage. In addition, MTA will benchmark values for mechanical, thermal and functional performance and gives advice for testing concepts.

Activities
Based on the specified requirements the contractor/partner shall provide a candidate list of suitable foldcore manufacturers. A trade shall be performed for the most promising candidates from technical and economical point of view. The most promising technique which has the most probability to combine all functions successfully shall be selected and further matured based on a suitable set of test data.

Output
Relevant documentation shall be established and shall cover:

• Candidate screening and selection process
• Sample production and testing of characteristic core properties
• Production and test of vacuum panel incl. test plan and test report of selected vacuum panel configuration
• Final evaluation incl. prospect for serial concept and scaling possibilities

Benefits
High potential core material which is capable to combine all functions in one CFRP sandwich structure. This will enable new opportunities for all kinds of high-performance insulation purposes offered within the FLPP Space Transportation Ecosystem Bavaria, reducing cost and improving the quality of launcher & aerospace structures.