  An outstanding, multi-disciplinary goal of modern science is the study of the
diversity of potentially Earth-like planets and the search for life in them.
This goal requires a bold new generation of space telescopes, but even the most
ambitious designs yet hope to characterize several dozen potentially habitable
planets. Such a sample may be too small to truly understand the complexity of
exo-earths. We describe here a notional concept for a novel space observatory
designed to characterize 1,000 transiting exo-earth candidates. The Nautilus
concept is based on an array of inflatable spacecraft carrying very large
diameter (8.5m), very low-weight, multi-order diffractive optical elements
(MODE lenses) as light-collecting elements. The mirrors typical to current
space telescopes are replaced by MODE lenses with a 10 times lighter areal
density that are 100 times less sensitive to misalignments, enabling
light-weight structure. MODE lenses can be cost-effectively replicated through
molding. The Nautilus mission concept has a potential to greatly reduce
fabrication and launch costs, and mission risks compared to the current space
telescope paradigm through replicated components and identical, light-weight
unit telescopes. Nautilus is designed to survey transiting exo-earths for
biosignatures up to a distance of 300 pc, enabling a rigorous statistical
exploration of the frequency and properties of life-bearing planets and the
diversity of exo-earths.
