Future astrophysics missions will require lightweight, thermally stable, submillimeter reflectors in sizes of 4m and greater. To date, graphite fiber reinforced composite (GFRC) construction has been used in many cases to ideally meet the reflector needs of submillimeter and microwave instruments, but only in sizes upto 2m. This project significantly advances the size and accuracy capability of GFRC reflector technology for future missions by focusing on innovation in two limiting areas: precision mandrel fabrication, and core induced surface error. Mandrel cost and quality can often be thee most significant budget and schedule challenge to a reflector program. To reduce cost, recent commercial innovations in optical grinding and polishing will be investigated for applicability to fabrication of a 4m convex tool. A variety of traditional and non-conventional tool materials will be considered. No-mandrel assembly concepts will also be investigated. To improve reflector surface accuracy, improvement is needed to mitigate the anisotropic nature of GFRC core. Novel methods of attaching core elements to faceskins will be investigated, as well as alternative core materials and manufacturing approaches. Phase 1 will result in a preliminary point design for a 4m-class submm reflector. Concepts for improvement in mandrel cost and quality, and reduction of core induced surface error, will be defined. After verification of these concepts in early Phase 2, a 4m-class prototype reflector will be built and tested that demonstrates all key aspects of a multi-meter full-scale reflector design and build.