The Heliospheric Imager (HI) is part of the SECCHI suite of instruments on-board the two STEREO observatories launched in October 2006. The two HI instruments provide stereographic image pairs of solar coronal plasma and coronal mass ejections (CME) over a field of view ranging from 13 to 330 R₀. The HI instrument is a combination of two refractive optical systems with a two stage multi-vane baffle system. The key challenge of the instrument design is the rejection of the solar disk light by the front baffle, with total straylight attenuation at the detector level of the order of 10^-13 to 10^-15. Optical systems and baffles were designed and tested to reach the required rejection. This paper presents the pre-flight optical tests performed under vacuum on the two HI flight models in flight temperature conditions. These tests included an end-to-end straylight verification of the front baffle efficiency, a co-alignment and an optical calibration of the optical systems. A comparison of the theoretical predictions of the instrument response and performance with the calibration results is presented. The instrument in-flight photometric and stray light performance are also presented and compared with the expected results.

Date Published: 3 October 2007
PDF: 12 pages
Proc. SPIE 6689, Solar Physics and Space Weather Instrumentation II, 668906 (3 October 2007); doi: 10.1117/12.731098

Published in SPIE Proceedings Vol. 6689:
Solar Physics and Space Weather Instrumentation II
Silvano Fineschi; Rodney A. Viereck, Editor(s)