Cryogenic Insulation Standard Data and Methodologies (CTIS)

Extending some recent developments in the area of technical consensus standards for cryogenic thermal insulation systems, a preliminary Inter-Laboratory Study of foam insulation materials was performed by NASA Kennedy Space Center and LeTourneau University. The initial focus was ambient pressure cryogenic boil off testing using the Cryostat-400 flat-plate instrument. Completion of a test facility at LETU has enabled direct, comparative testing, using identical cryostat instruments and methods, and the production of standard thermal data sets for a number of materials under sub-ambient conditions. The two sets of measurements were analyzed and  indicate there is reasonable agreement between the two laboratories.Based on cryogenic boiloff calorimetry, new equipment and methods for testing thermal insulation systems have been successfully developed. These boiloff instruments (or cryostats) include both flat plate and cylindrical models and are applicable to a wide range of different materials under a wide range of test conditions. Test measurements are generally made at large temperature difference (boundary temperatures of 293 K and 78 K are typical) and include the full vacuum pressure range. Results are generally reported in effective thermal conductivity (k_e) and mean heat flux (q) through the insulation system. The new cryostat instruments provide an effective and reliable way to characterize the thermal performance of materials under sub-ambient conditions. Proven in through thousands of tests of hundreds of material systems, they have supported a wide range of aerospace, industry, and research projects. Boiloff testing technology is not just for cryogenic testing but is a cost-effective, field-representative methodology to test any material or system for applications at sub-ambient temperatures. This technology, when adequately coupled with a technical standards basis, can provide a cost-effective, field-representative methodology to test any material or system for applications at sub-ambient to cryogenic temperatures. A growing need for energy efficiency and cryogenic applications is creating a worldwide demand for improved thermal insulation systems for low temperatures. The need for thermal characterization of these systems and materials raises a corresponding need for insulation test standards and thermal data targeted for cryogenic-vacuum applications. Such standards have a strong correlation to energy, transportation, and environment and the advancement of new materials technologies in these areas. In conjunction with this project, two new standards on cryogenic insulation were recently published by ASTM International: C1774 and C740. Following the requirements of NPR 7120.10, Technical Standards for NASA Programs and Projects, the appropriate information in this report can be provided to the NASA Chief Engineer as input for NASA's annual report to NIST, as required by OMB Circular No. A-119, describing NASA's use of voluntary consensus standards and participation in the development of voluntary consensus standards and bodies.

Although some standards exist for thermal insulation, few address the sub-ambient temperature range and cold-side temperatures below 100 K. Standards for cryogenic insulation systems require cryostat testing and data analysis that will allow the development of the tools needed by design engineers and thermal analysts for the design of practical cryogenic systems. Thus, this critically important information can provide reliable data and methodologies for industrial efficiency and energy conservation.

The needs for technical standards for thermal insulation systems are growing in the US and worldwide. Energy efficiency and conservation needs -- of which thermal insulation systems are a key part -- are a top priority for economic, national security, and technological concerns. The emphasis on technical consensus standards is a clear directive from both government policy and market economic drivers.

Summarized here are the most recent and relevant government policy directives to encourage technical standards development and energy efficiency technology implementation. The reference federal agency is NASA and the target subject area is thermal insulation systems for low-temperature applications. Here is a list of the relevant documents:

1. OMB Circular No. A-119, Federal Participation in the Development and Use of Voluntary Consensus Standards and in Conformity Assessment Activities.
2. Memorandum for the Heads of Executive Departments and Agencies, document M-12-08 dated January 17, 2012.
3. NPR 7120.10, Technical Standards for NASA Programs and Projects, Effective Date: April 22, 2011.

On February 4, 2011, the President released A Strategy for American Innovation: Securing Our Economic Growth and Prosperity and directed Federal agencies to increase their efforts to catalyze technology breakthroughs to advance national priorities.  Pursuant to the Strategy for American Innovation, the Office of Science and Technology Policy (OSTP), the Office of Management and Budget (OMB), and the Office of the United States Trade Representative (USTR) are the Memorandum for the Heads of Executive Departments and Agencies was issued to clarify principles guiding Federal Government engagement in standards activities that can help address national priorities.

This R&D project was formulated in response to these agency and national objectives for technical standards. A preliminary Inter-Laboratory Study of foam insulation materials was conducted by NASA Kennedy Space Center (KSC) and LeTourneau University (LETU). The initial focus was ambient pressure (no vacuum) cryogenic boil off testing using two identical Cryostat-400 flat-plate instruments. Completion of a new test facility at LETU has enabled comparative testing, using similar methods, and the production of standard thermal data sets for cellular glass insulation material under cryogenic conditions. Test measurements were made at both KSC and LETU for comparative analysis. The results show reasonable agreement between the two laboratories. These initial measurements were made at the approximate boundary temperatures of 293 K and 78 K, the results of which are reported in comparative effective thermal conductivity (comparative k_e) and mean heat flux (q).

The main challenge is the production of standardized thermal data sets for cryogenic insulation materials and systems. This project took up the challenge and made progress in three ways. The first was to produce a cataloged set of reference test specimens of cellular glass material. Other materials have been identified for future reference test specimens. Second was to conduct a preliminary interlaboratory study of the cellular glass material using the same equipment and methods (Cryostat-400 instrument). The third way was to show the practicality of using boiloff calorimetry to obtain thermal data for stack-ups of different materials (composite panels and insulation materials alike). The boiloff method, being a direct measure of heat energy, provides effective test solutions where other existing commercial methods fall short or are not possible.

In conjunction with this project, two new standards on cryogenic insulation were recently published by ASTM International: C1774 and C740. Following the requirements of NPR 7120.10, Technical Standards for NASA Programs and Projects, the appropriate information in this report can be provided to the NASA Chief Engineer as input for NASA's annual report to NIST, as required by OMB Circular No. A-119, describing NASA's use of voluntary consensus standards and participation in the development of voluntary consensus standards and bodies. Further standards in the area of cryogenic insulation systems have been targeted for future development.

This project involved a number of tasks that were synergetic with other projects under Advanced Exploration Systems, Center Innovation Fund, Game Changing Technology, and others. Compliance issues associated with PVS systems requirements was a major hit on resources in 2013 thus making this leveraging among projects crucial for this work. Three New Technology Reports, three peer-reviewed publications, and one full patent application were also produced in conjunction with this project. Additonal publications and patents are pending.