Solar Physics 217 (2), 319−347, 2003
© Kluwer Academic Pub.

The Solar Mass Ejection Imager (SMEI)

C.J. Eyles, G.M. Simnett, M.P. Cooke
School of Physics and Space Research, University of Birmingham, B15 2TT, UK

B.V. Jackson, A. Buffington and P.P. Hick
Center for Astrophysics and Space Sciences, University of California, San Diego, CA 92093-0424, USA

N.R. Waltham and J.M. King
Space Science Department, Rutherford-Appleton Laboratory, Chilton, OX11 0QX, UK

P.A. Anderson
Astronomy Department, Center for Space Physics, Boston University, Boston, MA, USA

P.E. Holladay
Air Force Research Laboratory/VSBS, 29, Randolph Road, Hanscom AFB, MA 01731-3010, USA


We describe an instrument (SMEI) which has been specifically designed to detect and forecast the arrival of solar mass ejections and other heliospheric structures which are moving towards the Earth. Such events may cause geomagnetic storms, with resulting radiation hazards and disruption to military and commercial communications; damage to Earth-orbiting spacecraft; and also terrestrial effects such as surges in transcontinental power transmission lines. The detectors are sensitive over the optical wave-band, which is measured using CCD cameras. SMEI was launched on 6 January 2003 on the Coriolis spacecraft into a Sun-synchronous polar orbit as part of the US DoD Space Test Programme. The instrument contains three cameras, each with a field of view of 60° × 3°, which are mounted onto the spacecraft such that they scan most of the sky every 102-min orbit. The sensitivity is such that changes in sky brightness equivalent to a tenth magnitude star in one square degree of sky may be detected. Each camera takes an image every 4 s. The normal telemetry rate is 128 kbits s-1. In order to extract the emission from a typical large coronal mass ejection, stellar images and the signal from the zodiacal dust cloud must be subtracted. This requires accurate relative photometry to 0.1%. One consequence is that images of stars and the zodiacal cloud will be measured to this photometric accuracy once per orbit. This will enable studies of transient zodiacal cloud phenomena, flare stars, supernovae, comets, and other varying point-like objects.