Current cryogenic insulation materials suffer from various drawbacks including high cost and weight, lack of structural or load-bearing capability, fabrication complexity, and property anisotropy. A need clearly exists for lightweight thermal insulation that is isotropic and structurally capable with high thermal performance, while also offering reduced fabrication and installation complexity, and lower cost.
The potential exists to adapt and optimize existing aerogel-filled structural foam for the cryogenic insulation application, taking advantage of the thermal and mechanical benefits of each component while offering low cost and manufacturability in complex shapes. In the current work, the feasibility of using aerogel-filled foam in cryogenic applications was demonstrated through low-density foam and aerogel fabrication, and supporting design and analysis. Thermal performance was characterized by preliminary thermal conductivity screening tests followed by more extensive testing during which thermal conductivity was measured at cryogenic temperature and pressures ranging from ambient to high vacuum.
A structure composed of highly porous structural foam filled with a highly insulating aerogel was developed and optimized for the cryogenic insulation application. The structure differed from previous work involving use of aerogel-filled foams for high-temperature applications in that cured (non-pyrolyzed) foam and cured resorcinol formaldehyde (RF) aerogel materials were utilized, allowing for a reduction in both thermal conductivity and density relative to the high-temperature, all-carbon (fully pyrolyzed) versions used previously.
Substantial improvements were made in reducing the density of the aerogel and structural foam components, resulting in a significant decrease in thermal conductivity. The thermal conductivity and density were considered to be in range for many cryogenic insulation applications. The crushable foam structure allows for the material to be press-fit over complex features within a system, whereas application of conventional multilayer insulation over such areas is difficult.
The potential application of this technology as a lightweight structural insulator for cryogenic propellant tanks and lines, both at ambient pressure and under high vacuum, may prove an enabling technology for future space and planetary missions and ground operations. Passive thermal control is required for zero-boiloff storage of cryogens for both long-term on the lunar surface and short-term in orbit. The aerogel-filled structural foam cryogenic insulation will offer improved thermal performance over current materials, with the added benefits of reduced weight, and fabrication and installation costs relative to conventional multilayer insulation.