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
Abstract
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.