Proc. SPIE 4853, 490−503, 2003
Innovative Telescopes and Instrumentation for Solar Astrophysics
S.L. Keil and S.V. Avakyan (eds.)
© SPIE − The International Society for Optical Engineering

Calculations for, and laboratory measurements of a multistage labyrinthine baffle for SMEI

A. Buffington, B.V. Jackson and P. Hick
Center for Astrophysics and Space Sciences, University of California San Diego


The spaceborne Solar Mass Ejection Imager (SMEI) is scheduled for launch into near-earth orbit (>800 km) in early 2003. Three SMEI CCD cameras on the zenith-oriented CORIOLIS spacecraft cover most of the sky each 100-minute orbit. Data from this instrument will provide precision visible-light photometric maps. Once starlight and other constant or slowly varying backgrounds are subtracted, the residue is mostly sunlight that has Thomson-scattered from heliospheric electrons. These maps will enable 3-dimensional tomographic reconstruction of heliospheric density and velocity. The SMEI design provides three cameras, one of which views to within 18 degrees of the solar disk with a field of view 60° long by 3° wide. Placed end-to-end, three fields of view then cover a nearly 180° long strip that sweeps out the sky over each orbit. The 3-dimensional tomographic analysis requires 0.1% photometry and background-light reduction below one S10 (the brightness equivalent of a 10th magnitude star per square degree). Thus 10-15 of surface-brightness reduction is required relative to the solar disk. The SMEI labyrinthine baffle provides roughly 10-10 of this reduction; the subsequent optics provides the remainder. We describe the baffle design and present laboratory measurements of prototypes that confirm performance at this level.