Kinetic Integrated Thermal Protection System (KnITPS)

Use the flexibility and shape formation possibilities inherent in knitting to form thermal protection systems that can be custom fitted to a heat shield carrier structure. Knitted TPS could potentially be used to form 3D and integrated structures. For example, internal struts could be knitted directly into a 2D face sheet, making the joint an integral part of the structure. Ablative thermal protection materials made from carbon fiber substrates impregnated with resin, especially phenolic, and various other components have and are being developed for demanding atmospheric entries. The carbon fiber can be short or chopped fiber arranged in a rigid (e.g. FiberForm) or flexible substrate (felts) or woven into 2D or 3D structures. The introduction of other fibers to make graded or tailored microstructures are being investigated in a current OCT program. An alternative way to form the substrate and place fibers at exact locations to control local properties is through knitting. Although these techniques are commonly associated with the manufacture of clothing, they have potential advantages in forming substrates for TPS. Knitted fabrics are much more elastic than woven fabrics, and can stretch up to 500%, depending upon the yarn and pattern. Knitted fabrics will drape and fit a form, and knitting can be used to shape a part, including introduction of holes and tabs. Introduction of other fibers in sections or by the stitch is well-known. Commercial knitting companies can make complex structures from a variety of yarns. The field of textile technology has developed many techniques to form and model structures that could be adapted for the development of thermal protection system, including 3D and graded structures. It should be possible to form a thermal protection material by infiltrating phenolic or other polymers and/or additives into the knitted carbon structure. Infiltration techniques developed for rigid and other preforms would be modified for these structures. The advantage of the proposed technique is the ability to make a thermal protection system that can be shaped in advance but has the flexibility to conform to complex shapes. The approach will reduce joints and seams. If successful this approach will provide another tool to solve complex issues in ensuring safe, reliable and efficient thermal protection systems for NASA. More »