Description: A key technology for space exploration including extended lunar missions and lunar surface systems operations is the maturation and demonstration of large-scale lightweight composite fuel storage tanks and associated support structure and penetrations. Spacecraft may exceed mass and volume limits. Development needs for a composite tank include integration of multi-layer insulation (MLI) with micro-meteoroid protection, tank support structure/isolators, other penetrations and development for all composite and/or composite with a metallic inner liner, mitigation of permeability, design, analysis/modeling, material properties at cryogen temperatures and manufacturing processes. Challenges needing to be addressed include long-term storage of cryogens, micro-cracking, composite/metal interfaces, and permeation (measurement and testing). Due to budget and schedule constraints the project was not able to address many of the needs and challenges for infusing a composite cryotank into exploration systems including landers, depots and surface infrastructure. The CTE-A project addressed the materials and permeation areas to increase readiness levels of light-weight composite cryotanks. The project has advanced NASA's and industry's position with respect to cryogenic composite tanks by developing material property data, a low-cost permeation assessment capability and conducting NDE assessments for microcrack identification. Follow-on work under the cryogenic fluid management (CFM) project could include compatibility assessments for long duration service life, performing design trade studies and down selecting potential demonstration permeability/boiloff test articles, and integrating previously developed technologies to reduce boil off for use with tank architectures. There were three focus areas for the CTE-A project. The first area was materials properties at cryogenic temperatures. Composite material properties at cryogenic (LOX and/or LH2) temperatures are scarce. The second area was developing nondestructive evaluation (NDE) methods for detection of microcracks in composite laminates. Microcracking in composites at cryogenic temperatures poses a challenge for the long-term use of all-composite pressure vessels because it leads to leakage. Therefore, the ability to nondestructively evaluate microcracking is needed to assess material suitability for cryogenic applications and to monitor the health of composite cryotanks in service. The third area was cost-effective permeability test methods. Cost of current permeability test methods have increased over the last several years.

Benefits: The CTE-A technology offers the prospect to reduce mass and improve performance for cryotank applications using composite tanks. The project worked to better understand material and material forms at cryogenic temperatures, and methods to test those materials for potential use in cryotank applications for missions such as Human Lander Systems (HLS), launch vehicles and lunar/on-orbit fuel depots. The objective of the cryotank technology is to reduce mass by 10% (threshold) to 30% (stretch) and reduce the level of boil off experienced. There is the potential to save 50 to 100 pounds for lander architectures and upwards of 500 pounds for NTP applications. These mass savings are a 1:1 ratio between savings and payload. Another objective is to understand and measure the system level permeation, demonstrate and quantify thermal performance improvements and understand integrated attachment concepts to minimize heat leaks. The project made advancements in understanding materials through mechanical tests at cryogenic temps, permeation testing and NDE. The project provided composite material property data in a cryogen environment. These properties, that are needed for a habitat or long-term field applications, are scarce at LOX and LH2 temperatures.