The external starshade is a method for the direct detection and spectral characterization of terrestrial planets around other stars, a key goal identified in ASTRO2010. Tests of starshades have been and continue to be conducted in the lab and in the field using non-collimated light sources. We extend the current approach to performing night-time observations of astronomical objects using small-scale (10-30cm) starshades and the McMath-Pierce Solar Telescope at Kitt Peak National Observatory. This configuration allows us to make measurements of stars with a Fresnel number close to those expected in proposed full-scale space configurations. We present the results of our engineering runs conducted in 2015.
The external starshade is a method for the direct detection and spectral characterization of terrestrial planets
around other stars, a key goal identified in ASTRO2010. In an effort to validate the starlight-suppression performance of
the starshade, we have measured contrast better than 1×10-9 using 60 cm starshades at points just beyond the starshade
tips. These measurements were made over a 50% spectral bandpass, using an incoherent light source (a white LED), and
in challenging outdoor test environments. Our experimental setup is designed to provide starshade to telescope
separation and telescope aperture size that are scaled as closely as possible to the flight system. The measurements
confirm not only the overall starlight-suppression capability of the starshade concept but also the robustness of the setup
to optical disturbances such as atmospheric effects at the test site. The spectral coverage is limited only by the optics and
detectors in our test setup, not by the starshade itself. Here we describe our latest results as well as detailed comparisons
of the measured results to model predictions. Plans and status of the next phase of ground testing are also discussed.
In the field of exoplanet detection and characterization, the use of a starshade, an external occulter in front of a telescope
at large separations, has been identified as one of the highly promising methods to achieve the necessary high contrast
imagery. Control of scattered sunlight from the edges of the starshade into the telescope has been identified as one of the
key technology development areas in order to make the starshade feasible. Modeling of the scattered light has resulted
in very different results so a campaign of experimentation with edge samples was undertaken to attempt to understand
the discrepancies.
Here, we present our results from the measurement of select samples of materials which would be suitable for manufacturing
the starshade edge, and related models. We have focused on coating metallic samples for ease of fabrication:
Titanium, Aluminum, and a Beryllium Copper alloy. Using standard machine shop methods, we fabricated samples
which had sharp edges with radius of curvature (RoC) between 15 and 20 μm. We then had these samples coated by two
suppliers to evaluate how well these coating types would conform to the edge and provide scatter suppression. The
results of scatter measurements of these coated edge samples are presented. These scatter results have been incorporated
into a new geometrical model in FRED which includes the details of the starshade mechanical model. This model
predicts both the magnitude and distribution of the scattered sunlight in the image plane of a nominal telescope. We
present these results, including a first effort at modeling the Solar System at 10 pc as seen by this mission architecture.
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