ASHI is a visible-light photometer covering a full hemisphere of sky. Its lightweight design is suitable for deployment on top of a balloon, where its heliospheric imagery and stray-light capability can be evaluated, or for a long mission be deployed on a spacecraft. ASHI's data analysis subtracts stars brighter than 6th magnitude down to a residue of 0.1% of their original brightness, and after this subtraction, is capable of differential photometry in most of its 1 X 1 degree sky bins.
ASHI consists of a smooth, slightly curved corral 17" in diameter which eliminates stray light from bright objects located further than 2 degrees below a plane perpendicular to its axis. The corral encloses an optical system incorporating a fisheye lens which views along the optical axis down to ~87 degrees, just over the top of the corral. The fisheye lens also records an image from two flat mirrors in order to peer just over the corral in the direction of the Sun.