Advancements in precision edges for a starshade external occulter

A starshade enables direct imaging of Earth-like exoplanets in the habitable zone of nearby stars by suppressing light from a target star so that orbiting planets are revealed. The perimeter of a starshade, known as the optical edge, has two critical functions. First, it must meet a precise in-plane profile specification to form a deep shadow in which the telescope is placed. Second, it must minimize reflected sunlight, as scattered sunlight significantly degrades the achievable contrast. Prior work on small scales and in a laboratory environment has shown that these requirements can be met using a chemically etched amorphous metal foil. This paper describes the next step of development, a first ever demonstration of assembled optical edge segments that meet both requirements simultaneously. The segments were constructed using space-compatible components and tested to relevant thermal and mechanical environments. A thorough assessment of edge performance, including in-plane profile, sunlight scatter and mechanical survivability was performed both before and after environmental testing. Furthermore, a custom scattered light testbed has been developed to quantify the magnitude of scattered sunlight over the entire length of the optical edge. The results of this study inform the future development of optical edge technology and pave the way towards eventual flight implementation.