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Proceedings Paper

Stray light analysis and testing of the SoloHI (solar orbiter heliospheric imager) and WISPR (wide field imager for solar probe) heliospheric imagers
Author(s): Arnaud F. R. Thernisien; Russell A. Howard; Clarence Korendyke; Tim Carter; Damien Chua; Simon Plunkett
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Paper Abstract

The techniques for stray light analysis, optimization and testing are described for two space telescopes that observe the solar corona: the Solar Orbiter Heliospheric Imager (SoloHI) that will fly on the ESA Solar Orbiter (SolO), and the Wide Field Imager for Solar Probe (WISPR) that will fly on the NASA Parker Solar Probe (PSP) mission. Imaging the solar corona is challenging, because the corona is six orders of magnitude dimmer than the Sun surface at the limb, and the coronal brightness continues to decrease to ten orders of magnitude below the Sun limb above 5° elongation from Sun center. The SoloHI and WISPR instruments are located behind their respective spacecraft heat shield. Each spacecraft heat shield does not block the instrument field of view above the solar limb, but will prevent direct sunlight entering the instrument aperture. To satisfy the instrument stray light attenuation required to observe the solar corona, an additional set of instrument baffles were designed and tested for successive diffraction of the heat shield diffracted light before entering the telescope entrance pupil. A semi empirical model of diffraction was used to design the baffles, and tests of the flight models were performed in flight like conditions with the aim of verifying the rejection of the design. Test data showed that the baffle systems behaved as expected. A second source of stray light is due to reflections of the sunlight off of the spacecraft structures and towards the instruments. This is especially the case for SoloHI where one of the spacecraft 8m tall solar arrays is located behind the telescope and reflects sunlight back onto the instrument baffles. The SoloHI baffle design had to be adjusted to mitigate that component, which was achieved by modifying their geometry and their optical coating. Laboratory tests of the flight model were performed. The test data were correlated with the predictions of a ray tracing model, which enabled the fine tuning of the model. Finally, end-to-end ray tracing was used to predict the stray light for the flight conditions.

Paper Details

Date Published: 6 July 2018
PDF: 19 pages
Proc. SPIE 10698, Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave, 106980E (6 July 2018); doi: 10.1117/12.2313645
Show Author Affiliations
Arnaud F. R. Thernisien, U.S. Naval Research Lab. (United States)
Russell A. Howard, U.S. Naval Research Lab. (United States)
Clarence Korendyke, U.S. Naval Research Lab. (United States)
Tim Carter, U.S. Naval Research Lab. (United States)
Damien Chua, U.S. Naval Research Lab. (United States)
Simon Plunkett, U.S. Naval Research Lab. (United States)


Published in SPIE Proceedings Vol. 10698:
Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave
Makenzie Lystrup; Howard A. MacEwen; Giovanni G. Fazio; Natalie Batalha; Nicholas Siegler; Edward C. Tong, Editor(s)

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