Thermal Conductivity of Lofty Nonwovens in Space and Planetary Vacuum Environment

For planetary exploration, new thermal insulation materials are needed to deal with unique environmental conditions presented to extravehicular activity (EVA). The thermal insulation material and system used in the existing space suit were specifically designed for low orbit environment. They are not adequate for low vacuum condition commonly found in planetary environments with a gas atmosphere. This study attempts to identify the types of lofty nonwoven thermal insulation materials and the construction parameters that yield the best performance for such application. Lofty nonwovens with different construction parameters are evaluated for their thermal conductivity performance. Three different types of fiber material: solid round fiber, hollow fiber, and grooved fiber, with various denier, needling intensity, and web density were evaluated. They were tested in three different vacuum conditions: low orbit high vacuum (10^–5 torr), intermediate vacuum (10^–3 torr), and Mars atmosphere low vacuum (8 torr), using the guarded-hot-plate method. The performance of the materials was correlated with each construction parameter. The results show that the grooved fiber material is the best insulation material among the three types of fiber tested. The geometry of the grooved fiber lengthens the path for heat transfer and lowers the thermal conductivity of the material. More testing and data are needed in order to validate the trend to relate the thermal conductivity performance of the materials to the fiber size, needle intensity, and web density of the materials.