The development of ultra-light fibrous substrate mirrors allows serious contemplation of large multi-mirror space telescopes using rigid segments. Mirrors made of silica and alumina fibers have a small coefficient of thermal expansion and a density competitive with inflatable structures. Furthermore, they are without the imagery problems caused by non parabolic figures, gaseous expansion and contraction, tidal distortion of large gas filled structures, leaks, and long lived transient mirror perturbations caused by intentional pointing and tracking movements, micrometeor and space debris impacts, and mechanical vibrations. Fibrous substrate primary mirrors also have logistical advantages, since segments can be fabricated in orbit from small amounts of dense raw materials. One space shuttle flight, lifting about half its payload capacity, is adequate to transport all the material necessary to fabricate substrates for a one hundred meter telescope whose primary mirror consists of 12,086 hexagonal segments, each having a diameter of 1 meter and an area of 0.6495 square meters.